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Objectives: To investigate diet-exercise interactions related to bone markers in elite endurance athletes after a 3.5-week ketogenic low-carbohydrate, high-fat (LCHF) diet and subsequent restoration of carbohydrate (CHO) feeding. Methods: World-class race walkers (25 male, 5 female) completed 3.5-weeks of energy-matched (220 kJ·kg·d−1) high CHO (HCHO; 8.6 g·kg·d−1 CHO, 2.1 g·kg·d−1 protein, 1.2 g·kg·d−1 fat) or LCHF (0.5 g·kg·d−1 CHO, 2.1 g·kg·d−1 protein, 75–80% of energy from fat) diet followed by acute CHO restoration. Serum markers of bone breakdown (cross-linked C-terminal telopeptide of type I collagen, CTX), formation (procollagen 1 N-terminal propeptide, P1NP) and metabolism (osteocalcin, OC) were assessed at rest (fasting and 2 h post meal) and after exercise (0 and 3 h) at Baseline, after the 3.5-week intervention (Adaptation) and after acute CHO feeding (Restoration). Results: After Adaptation, LCHF increased fasting CTX concentrations above Baseline (p = 0.007, Cohen's d = 0.69), while P1NP (p < 0.001, d = 0.99) and OC (p < 0.001, d = 1.39) levels decreased. Post-exercise, LCHF increased CTX concentrations above Baseline (p = 0.001, d = 1.67) and above HCHO (p < 0.001, d = 0.62), while P1NP (p < 0.001, d = 0.85) and OC concentrations decreased (p < 0.001, d = 0.99) during exercise. Exercise-related area under curve (AUC) for CTX was increased by LCHF after Adaptation (p = 0.001, d = 1.52), with decreases in P1NP (p < 0.001, d = 1.27) and OC (p < 0.001, d = 2.0). CHO restoration recovered post-exercise CTX and CTX exercise-related AUC, while concentrations and exercise-related AUC for P1NP and OC remained suppressed for LCHF (p = 1.000 compared to Adaptation). Conclusion: Markers of bone modeling/remodeling were impaired after short-term LCHF diet, and only a marker of resorption recovered after acute CHO restoration. Long-term studies of the effects of LCHF on bone health are warranted.
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published: 21 January 2020
doi: 10.3389/fendo.2019.00880
Frontiers in Endocrinology | 1January 2020 | Volume 10 | Article 880
Edited by:
Gordon L. Klein,
University of Texas Medical Branch at
Galveston, United States
Reviewed by:
Peter Ebeling,
Monash University, Australia
Hasmik Jasmine Samvelyan,
Edinburgh Napier University,
United Kingdom
Craig Sale,
Nottingham Trent University,
United Kingdom
Gustavo A. Nader,
Pennsylvania State University (PSU),
United States
Louise M. Burke
These authors have contributed
equally to this work
Specialty section:
This article was submitted to
Bone Research,
a section of the journal
Frontiers in Endocrinology
Received: 04 September 2019
Accepted: 02 December 2019
Published: 21 January 2020
Heikura IA, Burke LM, Hawley JA,
Ross ML, Garvican-Lewis L,
Sharma AP, McKay AKA, Leckey JJ,
Welvaert M, McCall L and
Ackerman KE (2020) A Short-Term
Ketogenic Diet Impairs Markers of
Bone Health in Response to Exercise.
Front. Endocrinol. 10:880.
doi: 10.3389/fendo.2019.00880
A Short-Term Ketogenic Diet Impairs
Markers of Bone Health in Response
to Exercise
Ida A. Heikura 1,2† , Louise M. Burke 1,2
*, John A. Hawley 2, Megan L. Ross 1,2 ,
Laura Garvican-Lewis 1,2 , Avish P. Sharma 1, 3, Alannah K. A. McKay 1, 4, Jill J. Leckey 2,
Marijke Welvaert 1,5,6 , Lauren McCall 7and Kathryn E. Ackerman 7,8
1Australian Institute of Sport, Canberra, ACT, Australia, 2Exercise and Nutrition Research Program, Mary MacKillop Institute
for Health Research, Australian Catholic University, Melbourne, VIC, Australia, 3Griffith Sports Physiology and Performance,
School of Allied Health Sciences, Griffith University, Gold Coast, QLD, Australia, 4School of Human Sciences (Exercise and
Sport Science), The University of Western Australia, Crawley, WA, Australia, 5University of Canberra Research Institute for
Sport and Exercise, Canberra, ACT, Australia, 6Statistical Consulting Unit, Australian National University, Canberra, ACT,
Australia, 7Division of Sports Medicine, Boston Children’s Hospital, Boston, MA, United States, 8Neuroendocrine Unit,
Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States
Objectives: To investigate diet-exercise interactions related to bone markers in elite
endurance athletes after a 3.5-week ketogenic low-carbohydrate, high-fat (LCHF) diet
and subsequent restoration of carbohydrate (CHO) feeding.
Methods: World-class race walkers (25 male, 5 female) completed 3.5-weeks of
energy-matched (220 kJ·kg·d1) high CHO (HCHO; 8.6 g·kg·d1CHO, 2.1 g·kg·d1
protein, 1.2 g·kg·d1fat) or LCHF (0.5 g·kg·d1CHO, 2.1 g·kg·d1protein, 75–80%
of energy from fat) diet followed by acute CHO restoration. Serum markers of bone
breakdown (cross-linked C-terminal telopeptide of type I collagen, CTX), formation
(procollagen 1 N-terminal propeptide, P1NP) and metabolism (osteocalcin, OC) were
assessed at rest (fasting and 2 h post meal) and after exercise (0 and 3 h) at Baseline,
after the 3.5-week intervention (Adaptation) and after acute CHO feeding (Restoration).
Results: After Adaptation, LCHF increased fasting CTX concentrations above Baseline
(p=0.007, Cohen’s d=0.69), while P1NP (p<0.001, d=0.99) and OC (p<0.001,
d=1.39) levels decreased. Post-exercise, LCHF increased CTX concentrations above
Baseline (p=0.001, d=1.67) and above HCHO (p<0.001, d=0.62), while P1NP
(p<0.001, d=0.85) and OC concentrations decreased (p<0.001, d=0.99) during
exercise. Exercise-related area under curve (AUC) for CTX was increased by LCHF after
Adaptation (p=0.001, d=1.52), with decreases in P1NP (p<0.001, d=1.27)
and OC (p<0.001, d=2.0). CHO restoration recovered post-exercise CTX and CTX
exercise-related AUC, while concentrations and exercise-related AUC for P1NP and OC
remained suppressed for LCHF (p=1.000 compared to Adaptation).
Conclusion: Markers of bone modeling/remodeling were impaired after short-term
LCHF diet, and only a marker of resorption recovered after acute CHO restoration.
Long-term studies of the effects of LCHF on bone health are warranted.
Keywords: ketogenic diet, bone health, exercise, nutrition, endurance athletes
Heikura et al. Ketogenic Diet Impairs Bone Markers
Despite the generally positive effects of exercise in promoting
bone health, bone injuries represent a challenge to consistent
training and competition in high performance sport (1). This, in
part, is due to the interaction of dietary factors (e.g., low energy
availability, poor vitamin D status, inadequate calcium intake)
with unique features of the exercise program [e.g., minimal
or excessive bone loading associated with weight- and non-
weight-bearing sports, poor biomechanics (1,2)]. Low energy
availability (a mismatch between energy intake and the energy
cost of exercise) occurs in both female and male athletes (2)
and impairs bone health via direct (uncoupled bone turnover
with increased resorption rates) and indirect (mediation by
reproductive and metabolic hormones) mechanisms (1). In
addition, carbohydrate (CHO) availability may also play a role
in bone health. Indeed, results from several studies show that
commencing endurance exercise with low compared to normal
or high glycogen availability stimulates the release of the cytokine
interleukin-6 (IL-6) from the exercising muscles (3,4). Among its
range of effects, IL-6 has been hypothesized to lead to enhanced
activity of the receptor activator of the nuclear factor K B-ligand,
which controls bone turnover by increasing osteoclastic activity
(thereby increasing bone breakdown) (5). In support of this
contention, bone resorption is acutely increased when CHO is
restricted before (6), during (7), and after (8) prolonged (1–2 h)
endurance (running) exercise, and may be linked to concomitant
increases in IL-6 concentrations (7). However, a recent study
has reported that acute reductions in CHO availability around
exercise mediated an increase in markers of bone resorption that
are independent of energy availability and circulating IL-6 (9).
Apparent effects on other markers of bone metabolism, such as
osteocalcin (OC) and the bone formation marker procollagen 1
N-terminal propeptide (P1NP) in these models have been small
(69), although a 24 h fast has been reported to reduce blood OC
concentrations in lightweight rowers (10).
Whether these changes in markers of bone metabolism persist
(or are amplified) after chronic exposure to low CHO availability
around exercise remains unknown, but is of relevance in view
of the promotion of a ketogenic low CHO-high fat (LCHF) diet
to athletes and its putative benefits for endurance performance
(11). To date, no studies have examined the effects of longer-
term restriction of CHO at rest or in relation to exercise, although
in animal models and children with intractable epilepsy, chronic
adaptation to a ketogenic LCHF diet is associated with poor bone
health (1216). In view of our recent observations of increased
post-exercise IL-6 concentrations in elite race walkers following
a 3.5-week adaptation to a LCHF diet (17), we investigated
the interaction of this diet and strenuous exercise on markers
of bone modeling/remodeling as secondary outcomes of our
larger study.
Thirty world-class athletes (25 male, 5 female race walkers; ages
27.7 ±3.4 yr, BMI 20.6 ±1.7 kg/m2) were recruited over
three separate training camps during preparation for the 2016
Summer Olympic Games and the 2017 World Championships,
and provided written informed consent in accordance with
the Human Ethics Committee of the Australian Institute of
Sport (ethics approval no. 20150802 and 20161201). Six male
participants undertook two camps, however two of these data
sets were incomplete due to insufficient tissue samples, resulting
in 4 participants who had completed two camps being included
in the final analysis. In addition, two additional (male) data sets
were excluded from the final analysis due to their inability to
complete one of the experimental trials due to injury (unrelated
to bone). Therefore, our final data set provided a total of 32
trials (n=28 participants, 23 males, 5 females) with data for
pre- (Baseline) and post-treatment (Adaptation), of which 18
trials (13 males, 5 females) also contributed to data from acute
restoration to a HCHO diet (Restoration). Participants and elite
coaches contributed to the concept and implementation of the
research camps, helping to prioritize the themes of interest
and contributing to the design of the training program and
test protocols.
Study Overview
Participants completed a 3.5-week block of intensified training
and laboratory and field testing, supported by either a high-
CHO (HCHO) or an isoenergetic LCHF diet (Figure 1,Table 1),
consumed under strict dietary control (18). Upon completion
of the 3.5-week dietary intervention, a subset of participants
(n=18) completed a further testing block under conditions
of acute high CHO availability. Markers of bone metabolism
were measured after an overnight fast, in response to an energy-
matched meal of nutrient composition matching the intervention
diet, and in response to a bout of strenuous exercise (19), at
Baseline, Adaptation, and Restoration (Figure 1).
Dietary Control
Details of dietary control are described briefly here; more details
are described in prior work (18). Participants were allocated
into HCHO and LCHF groups based on preference. Both diets
were isocaloric (Table 1), however dietary CHO and fat intakes
differed between groups during intervention. Study diets were
designed and individualized for each athlete by trained members
of the research team including registered sports dietitians, a
professional chef, and exercise physiologists. All meals were
weighed (food scales accurate to 2 g) and provided for athletes
at set meal times. In addition, a collection of snacks per
individual meal plans were provided to the athletes each day. Any
unconsumed items or changes made to menu plans were weighed
and recorded for final analysis of dietary intakes. Compliance
to the meal plans was assessed daily. Meal plans were designed
and final dietary analysis of actual intakes was conducted using
FoodWorks 8 Professional Program (Xyris Software Australia Pty
Ltd, Australia). Further analysis of intakes was completed using
Microsoft Excel.
Experimental Design
Testing at Baseline, Adaptation, and Restoration involved a
hybrid laboratory/field test of 25 km (males) or 19 km (females)
Frontiers in Endocrinology | 2January 2020 | Volume 10 | Article 880
Heikura et al. Ketogenic Diet Impairs Bone Markers
FIGURE 1 | Study flowchart and overview. Thirty-two data sets were gathered from 30 participants who participated in one or more training camps. After Baseline
testing on a carbohydrate-rich (HCHO) diet, they elected to follow a 3.5-week energy-matched dietary intervention of either HCHO or ketogenic low
carbohydrate-high fat (LCHF) principles. After Adaptation, the participants underwent an acute period of Restoration of high carbohydrate availability. At Baseline and
at the end (Adaptation) of this intervention, as well as after acute carbohydrate reintroduction (Restoration) they undertook a test block including a 25km (2 h) hybrid
laboratory/field race walking protocol at 75% VO2max. Venous blood samples were collected after an overnight fast, 2 h after an energy-matched breakfast based
on their diet (immediately pre-exercise), immediately post exercise and after 3 h of passive recovery during which an intervention-matched recovery shake was
consumed at 30 min. Blood samples were analyzed for serum concentrations of C-terminal telopeptide of type I collagen (CTX), procollagen 1 N-terminal propeptide
(P1NP), and osteocalcin (OC).
Frontiers in Endocrinology | 3January 2020 | Volume 10 | Article 880
Heikura et al. Ketogenic Diet Impairs Bone Markers
TABLE 1 | Dietary intakes in the HCHO and LCHF groups.
Intervention Restoration
HCHO (n=14) LCHF (n=18) HCHO (n=8) LCHF (n=10)
Energy (kJ·d1) 14,518 ±2,142 15,138 ±2,104 13,705 ±1,948 15,706 ±1,774
Energy (kJ·kg·d1) 229 ±13 227 ±23 219 ±16 239 ±27
Protein (g·d1) 133 ±22 143 ±19 132 ±24 151 ±18
Protein (g·kg·d1) 2.1 ±0.2 2.1 ±0.2 2.1 ±0.2 2.3 ±0.2
Fat (g·d1) 74 ±14 318 ±45*** 77 ±14 95 ±12**$$$
Fat (g·kg·d1) 1.2 ±0.1 4.8 ±0.5*** 1.2 ±0.1 1.4 ±0.2**$$$
CHO (g·d1) 549 ±75 35 ±5*** 492 ±60$552 ±62$$$
CHO (g·kg·d1) 8.7 ±0.4 0.5 ±0.1*** 7.9 ±0.6$$ 8.4 ±1.0$$$
HCHO, high carbohydrate diet; LCHF, low carbohydrate high fat diet; CHO, carbohydrate.
**p<0.01, ***p<0.001 significant difference between diets.
$p<0.05, $$p<0.01, $$$ p<0.001 significantly different compared to Intervention.
at around 50 km race pace (75% of maximal oxygen uptake [VO2
max]) (Figure 1). Upon entering the laboratory in an overnight
fasted and rested state between 0600 and 0800 in the morning
(times were kept consistent within-participant), a cannula was
inserted into an antecubital vein for collection of blood samples
at rest (Fasting), immediately before exercise (2 h post-meal),
immediately after exercise (Post-ex) and 3 h post-exercise (3 h
post-ex). Blood was analyzed for concentrations of cross-linked
C-terminal telopeptide of type I collagen (CTX), P1NP and
total OC to determine the effects of dietary interventions and
exercise on bone metabolism. The cannulas were flushed with
3 ml of saline every 30 min throughout the trials. A standardized
breakfast (2 g·kg1CHO for both groups during Baseline
and Restoration, or an isocaloric low CHO option for LCHF
during Adaptation) was consumed 30 min after the first blood
sample, after which the participants rested for 120 min before
beginning the session. During the Baseline and Restoration
exercise test, both groups ingested glucose (60 g·h1) throughout
the test, while during Adaptation, isocaloric high fat snacks
were provided for the LCHF group. Upon completion of the
exercise test, the participants rested in the laboratory for a further
3 h, and received a standardized recovery shake (1.5 g·kg1
CHO for both groups during Baseline and Restoration, or an
isocaloric low CHO option for LCHF during Adaptation; both
shakes included 0.3 g·kg1protein) at 30 min post-exercise to
improve satiety.
Analysis of Serum Bone
Modeling/Remodeling Biomarkers
Blood samples were collected into a 3.5 mL EDTA BD Vacutainer
Plus SST II tube, and allowed to clot by standing at room
temperature for 2 h before centrifuging at 1,000 G for 10 min
for subsequent analysis of serum markers of bone resorption
(CTX), bone formation (P1NP) and overall bone metabolism
(OC). Analysis was undertaken by chemiluminescence on IDS-
iSYS (Immunodiagnostic Systems Limited; Boldon, Tyne and
Wear, UK). Inter-assay coefficient of variation as reported by
the manufacturer was 6.2, 4.6, and 6.1%, respectively. CVs
were determined as follows: OC: 6 serum controls were run,
using 3 reagents lots, in duplicate twice per day for 20 days,
on 2 analyzers; P1NP: 3 serum controls were run, using 3
reagent lots, in quadruplicates once per day for 20 days, on
2 analyzers; CTX: 5 serum controls were run, using 3 reagent
lots, in duplicate twice per day for 20 days, on 3 analyzers. In
addition to these tests, the laboratory ran quality control samples
throughout testing and the results were within the established
acceptable manufacturer ranges. The raw data for the analyses
of serum bone modeling/remodeling markers are provided in the
Supplementary Table to this publication.
Statistical Analyses
Statistical analyses were conducted using SPSS Statistics 22
software (INM, New York, USA) and R (R Core Team, 2018)
with a significance level set at p0.05. Normality of data was
checked with a Shapiro-Wilk test and visual inspection of residual
plots. General Linear Mixed models were fitted using the R
package lme4 (20) and included random intercepts for Subjects
and Camps to account for baseline inter individual heterogeneity
and the partial cross-over design. Because the estimated Camp
effect variance was 0, this random intercept was subsequently
removed to resolve boundary issues in the Restricted Maximum
Likelihood estimation. P-values were obtained using Type II
Wald F tests with Kenward-Roger degrees of freedom. Initial
models included all possible interactions but non-significant
interaction terms were dropped for ease of interpretation. Fasting
values and exercise-related area under curve [AUC; Pre-exercise
to 3 h post-exercise (21)] for all markers were compared with
a two-way mixed analysis of variance (ANOVA), with post-
hoc tests of Student’s t-tests for independent samples (between-
groups) and for paired samples (within-groups); where normality
was violated, Wilcoxon’s test and Mann-Whitney U-test were
used. Where a data point was missing, AUC was not calculated;
this resulted in exclusion of 1 participant in the CTX AUC
calculations, and 2 participants from both P1NP and OC
calculations. Effect sizes were calculated based on the Classical
Cohen’s dwhile accounting for the study design by using the
square root of the sum of all the variance components (specified
random effects and residual error) in the denominator. Data are
presented as means (95% confidence intervals [CI]).
Frontiers in Endocrinology | 4January 2020 | Volume 10 | Article 880
Heikura et al. Ketogenic Diet Impairs Bone Markers
Bone Modeling/Remodeling Biomarkers
During Fasting
Compared to Baseline, fasting concentrations of CTX were
increased after the LCHF diet (+22% [9, 35]: p=0.008, d=0.69),
with a decrease in P1NP (14% [19, 9]; p=0.001, d=0.99)
and OC (25% [35, 14]; p<0.001, d=1.39) levels
(Figure 2). In addition, the change in fasting P1NP (p<0.001,
d=1.64) and OC (p<0.001, d=1.78) after the 3.5-
week intervention was significantly different between the diets
(Figure 2).
Exercise Bone Markers
CTX decreased post-meal independent of dietary intervention
(Figures 3A,4A,p<0.001, d=1.63). At Adaptation, post-
exercise CTX concentrations in LCHF increased above Baseline
(p=0.001, d=1.67) and HCHO (p<0.001, d=0.62)
(Figure 3A). LCHF decreased P1NP (Figure 3B,p<0.001,
d=0.85) and OC across exercise (Figure 3C,p<0.001,
d=0.99) compared to Baseline. At Restoration, post-exercise
CTX returned to Baseline levels for LCHF (Figure 4A,p>0.05,
d=0.20 compared to Baseline), while concentrations of P1NP
(Figure 4B,p<0.001, d=0.23) and OC (Figure 4C,p<0.001,
d=0.21) remained suppressed across exercise.
Bone Marker Exercise Area Under Curve
At Adaptation, LCHF exercise-related AUC for CTX was greater
[+81% (54, 109); p<0.001, d=1.52] than Baseline, and
higher than HCHO (p=0.035, d=0.81) (Figure 3D). Exercise-
related AUC for P1NP decreased at Adaptation for LCHF
[19% (25, 12); p=0.003, d=1.27] compared with
Baseline and was lower than HCHO (p=0.009, d=1.03)
FIGURE 2 | Percentage change in fasting serum C-terminal telopeptide of
type I collagen (CTX), procollagen 1 N-terminal propeptide (P1NP) and
osteocalcin (OC) for high carbohydrate (HCHO; solid bars) and low CHO high
fat (LCHF; striped bars) after the 3.5-week dietary intervention. Data are means
±standard deviations. ***p<0.001 Significant between-group difference;
##p<0.01; ### p<0.001 Significant change from Baseline within-group.
(Figure 3E), with similar outcomes for OC [29% (35, 23);
p<0.001, d=2.0 and p<0.001, d=1.64, Figure 3F]. At
Restoration, LCHF experienced a return of exercise-related AUC
for CTX back to Baseline values [43% (21, 31); p=0.003,
d=1.08 compared to Adaptation and no difference compared
to HCHO; Figure 4D], meanwhile AUC for P1NP [+3% (17,
48), p=1.000 compared to Adaptation and p=0.009, d=1.50
compared to HCHO; Figure 4E], OC [3% (19, 14), p=1.000
compared to Adaptation and p=0.010, d=1.47 compared to
HCHO; Figure 4F] remained suppressed.
Our data reveal novel and robust evidence of acute and likely
negative effects on the bone modeling/remodeling process in
elite athletes after a short-term ketogenic LCHF diet, including
increased marker of resorption (at rest and post-exercise) and
decreased formation (at rest and across exercise), with only
partial recovery of these effects following acute restoration of
CHO availability. Long-term effects of such alterations remain
unknown, but may be detrimental to bone mineral density
(BMD) and bone strength, with major consequences to health
and performance. While ketogenic diets are of interest to athletes
due to their ability to induce substantial shifts in substrate
metabolism, increasing the contribution of fat-based fuels during
exercise (11), we have previously reported the downside of a
concomitantly greater oxygen cost and reduced performance of
sustained high-intensity endurance exercise (19). The current
study identifies further complexity in the interaction between
the ketogenic diet and exercise with respect to markers of
bone modeling/remodeling, in which catabolic processes are
augmented and anabolic processes are reduced.
The LCHF diet is also popular within the general community
for its purported health benefits, including rapid weight loss
and improved glycemic control (22). However, data from
animal studies (12,13) demonstrate that chronic LCHF diets
are associated with impaired bone growth, reduced bone
mineral content, compromised mechanical properties, and
slower fracture healing. Furthermore, increased bone loss has
been reported in children with intractable epilepsy placed on
a medically supervised LCHF diet for 6 months (14,15). In
contrast, adults with type 2 diabetes mellitus who self-selected
to consume a LCHF diet for 2 years experienced no changes in
spinal BMD in comparison to a “usual care” group (22). One
explanation for these divergent outcomes involves interactions
of the LCHF diet with the level of habitual contractile activity.
Indeed in mice, a LCHF diet negated the positive benefits of
exercise on BMD in trabecular bone (16), while in children
with epilepsy, the rate of bone loss was greater in the more
active patients (14). Therefore, the hormonal response to exercise
undertaken with low CHO availability was of particular interest
in our study.
Previous studies involving acute strategies of low CHO
availability around exercise have identified effects on bone
resorption, as measured by increased blood CTX concentrations.
For example, males who undertook 60 min of treadmill running
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Heikura et al. Ketogenic Diet Impairs Bone Markers
FIGURE 3 | Time course of changes in bone marker concentrations across exercise (left panel) and exercise area under curve (right panel) for serum C-terminal
telopeptide of type I collagen (CTX) (A,D), procollagen 1 N-terminal propeptide (P1NP) (B,E), and osteocalcin (OC) (C,F) after the 3.5-week dietary intervention. Black
bars/symbols represent Baseline, gray bars/symbols represent Adaptation. Squares and circles represent high carbohydrate (HCHO) and low carbohydrate high fat
(LCHF), respectively. Gray bars represent a hybrid laboratory/field 19–25 km walk test at 75% VO2max. Data are means ±standard deviations. ##p<0.01;
###p<0.001 denotes significant differences at time points or tests within diet groups. *p<0.05; **p<0.01; ***p<0.001 denotes significant differences between
diet groups at a specific time point.
at 65% VO2max following a CHO-rich breakfast (1 g·kg1)
showed small variations in CTX responses, but only around the
exercise period, while dietary effects on parathyroid hormone,
OC and P1NP were not detected (6). Meanwhile, a more
strenuous protocol (120 min at 70% VO2max) was associated
with an attenuation of acute (pre-exercise to 2 h post-exercise)
Frontiers in Endocrinology | 6January 2020 | Volume 10 | Article 880
Heikura et al. Ketogenic Diet Impairs Bone Markers
FIGURE 4 | Time course of changes in bone marker concentrations across exercise (left panel) and exercise area under curve (right panel) for serum C-terminal
telopeptide of type I collagen (CTX) (A,D), procollagen 1 N-terminal propeptide (P1NP) (B,E), and osteocalcin (OC) (C,F) after acute reintroduction of carbohydrate
(right panel). Gray bars/symbols represent Adaptation, and white bars/symbols represent Restoration. Squares and circles represent high carbohydrate (HCHO) and
low carbohydrate high fat (LCHF), respectively. Gray bars represent a hybrid laboratory/field 19–25 km walk test at 75% VO2max. Data are means ±standard
deviations. $$p<0.01; $$$ p>0.001 denotes significant within-group difference compared to Restoration. *p<0.05; **p<0.01; ***p<0.001 denotes significant
differences between diet groups at a specific time point.
concentrations of IL-6, CTX, and P1NP when CHO was
consumed (0.7 g·kg·h1) during exercise (7). However, OC was
unchanged by diet and no differences in markers of bone
metabolism were detected over the subsequent three days,
suggesting that these effects are transient and quickly reversed
(7). Short-term effects were also reported when 24 elite male
runners with energy-matched intake over an 8 d period were
divided into a group who consumed CHO before, during, and
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Heikura et al. Ketogenic Diet Impairs Bone Markers
immediately after each of their 13 training sessions (additional
total CHO) while the others consumed an artificially sweetened
placebo (23). Here, CTX concentrations were suppressed at
80 min of recovery following an interval training sessions in
the CHO group with no dietary effects on P1NP or OC;
furthermore, fasting concentrations of all markers were similar
at baseline and on the ninth morning (23). Finally, Hammond
and colleagues (9) investigated the independent effects of low
CHO availability and acute energy restriction during the recovery
from one session of high-intensity interval running and the
completion of a subsequent session (3.5 h into recovery). They
reported lower CTX concentrations in the high CHO (control)
diet compared with both of the other conditions across the
various acute responses to exercise-related feeding, while there
were no differences between the energy and CHO restricted trials.
Meanwhile, only energy restriction produced an increase in IL-
6 responses to exercise, and there were no differences in P1NP
concentrations between dietary treatments (9). Furthermore, 5
d of low vs. optimal energy availability, which also resulted in
a 2-fold difference in CHO availability, was shown to result in
a significant difference in the AUC of fasting CTX (+85 vs.
+15%, respectively) and P1NP (60 vs. 25%, respectively)
(24). To date, the only study to report an effect of acute
manipulations of CHO around exercise on bone formation
markers was that of Townsend et al. (8), in which the immediate
consumption of a protein-CHO feeding after a run to exhaustion
at 75% VO2max was associated with a suppression of the post-
exercise rise in CTX levels and a higher concentration of P1NP.
These authors concluded that immediate post-exercise meal
ingestion may benefit bone health compared to delayed feeding,
although the effects on CTX concentrations were reversed at
4 h post-exercise and a similar time course of P1NP changes
was not provided; therefore, it appears that the overall effect
on bone modeling/remodeling processes appears to follow meal
ingestion patterns.
The novelty of the current study was the interrogation of
the effects of prolonged adaptation to CHO restriction on bone
metabolism. Unlike the previous investigations, we identified
clear and consistent effects on bone metabolism at rest and in
response to exercise following 3.5-weeks of a ketogenic LCHF
diet (Figures 24), with increases in a marker of bone resorption
(CTX) and decreases in markers of bone formation (P1NP) and
metabolism (OC). Although some might argue that a complete
adaptation to a LCHF diet requires much longer than the 3.5-
week period utilized in the current study, it should be noted that
adaptations in substrate metabolism and exercise economy have
been reported across this (19,25), and much shorter (26), time
periods. Nevertheless, the current study is reflective of a shorter-
term adaptation to a LCHF diet and our findings warrant further
investigation across longer time periods.
Acute restoration of high CHO availability was only partially
effective in reversing these outcomes. Here, marker of bone
resorption returned to baseline with high CHO pre-exercise meal
and CHO ingestion throughout exercise, while the other markers
of bone metabolism remained suppressed, indicating impaired
overall balance of bone metabolism. This supports the concept
proposed by Hammond et al. (9) that CTX is responsive to acute
intake of CHO, possibly mediated through enteric hormone
secretion. Meanwhile, differences in muscle glycogen content,
which are not addressed by studies of acute feedings, may have a
greater effect on OC and P1NP concentrations. Given the serious
nature of injury risks and long-term outcomes of poor bone
health in later life in endurance athletes, further consideration
of the potential effects of the LCHF diet in exacerbating existing
risk factors for poor bone health is warranted. In particular, we
note that the impairment of bone metabolism around exercise
and recovery would involve a significant portion of the day in
athletes who undertake multiple training sessions, as well as being
superimposed on the changes identified at rest.
The interaction of diet and exercise on bone metabolism is
complex and requires more sophisticated investigation including
replication of the current findings. Furthermore, evolving
knowledge of inter-organ crosstalk suggests that outcomes
of altered bone metabolism may be more far-reaching than
the fate of the structural integrity of bone. Indeed, we note
the recognition of muscle and bone as endocrine organs,
with evidence that IL-6 released from contracting muscle has
autocrine, paracrine and endocrine effects (27). This includes
a purported feed-forward loop in which contraction-induced
stimulation of osteocalcin in myofibers promotes the release of
IL-6 and enhances muscle adaptation to exercise (27). Results
of the current study challenge this synergistic relationship
between osteocalcin signaling and IL-6, and remind us of
the pleiotropic nature of the molecules stimulated by diet-
exercise interactions.
The data analysis undertaken in this study was a secondary
outcome of our investigations of the ketogenic LCHF diet;
these were not specifically powered to optimally address the
potential effects on markers of bone modeling/remodeling.
However, the detection of changes in the IL-6 response to
prolonged exercise in our initial study (12) provided motivation
to examine possible downstream effects. Because an identical
protocol was undertaken in two separate studies of the LCHF
diet, we were able to pool data from these investigations to
double the sample size previously known to allow detection of
changes in metabolism and performance. Indeed, changes in
markers of bone metabolism in the response to the interaction
of exercise and the dietary treatments were clearly detected
with the pooled data, but were also identifiable in the case
of the smaller sample size of the carbohydrate restoration
arm of the current dataset. Therefore, we feel confident that
our data are robust and warrant further investigation of
this theme.
Despite recent interest in the potential benefits of LCHF diets on
endurance performance or metabolic adaptation, the long-term
health effects of this dietary intervention are largely unknown.
We are the first to show that a 3.5-week ketogenic LCHF diet
in elite endurance athletes has negative effects on the markers of
bone modeling/remodeling at rest and during a prolonged high
Frontiers in Endocrinology | 8January 2020 | Volume 10 | Article 880
Heikura et al. Ketogenic Diet Impairs Bone Markers
intensity exercise session. We also show only partial recovery
of these adaptations with acute restoration of CHO availability.
Given the injury risks and long-term outcomes underpinned by
poor bone health in later life, in athletes as well as individuals who
undertake exercise for health benefits, additional investigations
of the ketogenic diet and its role in perturbing bone metabolism
are warranted.
The datasets analyzed for this study were harvested from 2 trials
registered at Australian New Zealand Clinical Trial Registry
(ACTRN12619001015134 and ACTRN12619000794101), found
The studies involving human participants were reviewed and
approved by Australian Institute of Sport Ethics Committee. The
patients/participants provided their written informed consent to
participate in this study.
Conception and design of the experiments was undertaken
by IH, LB, MR, LG-L, AS, AM, JL, MW, LM, and KA.
Collection, assembly, analysis, and interpretation of data was
undertaken by IH, LB, MR, LG-L, AS, AM, JL, MW, LM,
and KA. Manuscript was prepared by IH, LB, KA, and JH.
All authors approved the final version of the manuscript. IH
and LB had full access to all the data in the study and take
responsibility for the integrity of the data and the accuracy of the
data analysis.
This study was funded by a Program Grant from the
Australian Catholic University Research Funds to Professor LB
(ACURF, 2017000034).
We thank our research colleagues and supporters of the
Supernova research series and acknowledge the commitment of
the elite race-walking community.
The Supplementary Material for this article can be found
online at:
Supplementary Table 1 | Individual data for the serum concentrations of bone
modeling/remodeling markers (CTX, P1NP and Osteocalcin) in response to
strenuous exercise (2 h race walking) and dietary interventions (high carbohydrate
and low carbohydrate high fat diets) in elite race walkers.
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Conflict of Interest: The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be construed as a
potential conflict of interest.
Copyright © 2020 Heikura, Burke, Hawley, Ross, Garvican-Lewis, Sharma, McKay,
Leckey, Welvaert, McCall and Ackerman. This is an open-access article distributed
under the terms of the Creative Commons Attribution License (CC BY). The use,
distribution or reproduction in other forums is permitted, provided the original
author(s) and the copyright owner(s) are credited and that the original publication
in this journal is cited, in accordance with accepted academic practice. No use,
distribution or reproduction is permitted which does not comply with these terms.
Frontiers in Endocrinology | 10 January 2020 | Volume 10 | Article 880
... (5) Although multiple factors are often at play, inadequate nutritional support is a key consideration for bone health. (6) Previous studies have identified a role for both overall energy availability (7,8) and carbohydrate availability (9)(10)(11) in the bone turnover response to exercise. However, because energy restriction involves a relative reduction in carbohydrate intake, it has been difficult to ascertain whether the effect on bone is due to inadequate energy or lack of carbohydrate. ...
... (23) Further, 3.5 weeks of a ketogenic (<50 À1 of carbohydrate) diet in elite racewalkers was observed to increase bone resorption (CTX) and decrease bone formation (P1NP) markers at both rest and across exercise. (11) Although there are no published long-term studies on athletes, evidence from both animal models (24) and children with intractable epilepsy being treated with a ketogenic diet (25) suggests that there may be a detrimental effect of the ketogenic diet on bone health, potentially due to carbohydrate restriction. A second interest in this diet is its ability to separate the effects of low carbohydrate availability from energy availability, allowing for further inquiry into the influences of macronutrients on health and performance, independent of overall energy intake. ...
... Participants Twenty-eight elite male racewalkers, eligible for participation in either national or international competition, were recruited for this study via convenience sampling. Based on previous work (11) investigating BTM responses to either a high carbohydrate or ketogenic diet, it was estimated that including 5-10 participants per group (osteocalcin: d = 2.00; CTX: d = 1.52; P1NP: d = 1.27) was appropriate to detect statistical significance with an alpha of 0.05 and power of 0.8 (GPower version; ...
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Bone stress injuries are common in athletes, resulting in time lost from training and competition. Diets that are low in energy availability have been associated with increased circulating bone resorption and reduced bone formation markers, particularly in response to prolonged exercise. However, studies have not separated the effects of low energy availability per se from the associated reduction in carbohydrate availability. The current study aimed to compare the effects of these two restricted states directly. In a parallel group design, 28 elite racewalkers completed two 6‐day phases. In the Baseline phase, all athletes adhered to a high carbohydrate/high energy availability diet (CON). During the Adaptation phase, athletes were allocated to one of three dietary groups: CON, low carbohydrate/high fat with high energy availability (LCHF), or low energy availability (LEA). At the end of each phase, a 25 km racewalk was completed, with venous blood taken fasted, pre‐exercise, and 0, 1, 3 h post‐exercise to measure carboxyterminal telopeptide (CTX), procollagen‐1 N‐terminal peptide (P1NP), and osteocalcin (carboxylated, gla‐OC; undercarboxylated, glu‐OC). Following Adaptation, LCHF showed decreased fasted P1NP (~26%; p<.0001, d=3.6), gla‐OC (~22%; p=.01, d=1.8), and glu‐OC (~41%; p=.004, d=2.1), which were all significantly different to CON (p<.01), whereas LEA demonstrated significant, but smaller, reductions in fasted P1NP (~14%; p=.02, d=1.7) and glu‐OC (~24%; p=.049, d=1.4). Both LCHF (p=.008, d=1.9) and LEA (p=.01, d=1.7) had significantly higher CTX pre‐ to 3 h post‐exercise but only LCHF showed lower P1NP concentrations (p<.0001, d=3.2). All markers remained unchanged from Baseline in CON. Short‐term carbohydrate restriction appears to result in reduced bone formation markers at rest and during exercise with further exercise‐related increases in a marker of bone resorption. Bone formation markers during exercise seem to be maintained with LEA although resorption increased. In contrast, nutritional support with adequate energy and carbohydrate appears to reduce unfavorable bone turnover responses to exercise in elite endurance athletes. This article is protected by copyright. All rights reserved.
... It has recently been addressed that OTS and RED-S have many shared pathways and symptoms initiated from a hypothalamic-pituitary dysfunction that can be influenced by low energy and/or low carbohydrate (CHO) availability (Stellingwerff et al., 2021). The role of low CHO availability (with or without the diagnosis of OTS/RED-S) have been linked to increased risk of developing NFOR and/or OTS in endurance athletes (Meeusen et al., 2013;Heikura et al., 2019;Stellingwerff et al., 2021). Interestingly, training with low CHO availability (i.e., "train low") have been suggested as a method to augment endurance adaptations (Burke, 2010;Bartlett et al., 2015). ...
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Purpose: To determine the main factors associated with unexpected underperformance and prospectively describe the holistic process of returning to sustainable world-class level in a male cross-country skier. Methods: Longitudinal training data was retrospectively analyzed across nine seasons (2012-2013 to 2020-2021), and categorized into training forms (endurance, strength, and speed), intensities [low- (LIT), moderate- (MIT), and high-intensity training (HIT)], and modes (specific and non-specific). Performance data was obtained from the International Ski and Snowboard Federation. Following two seasons of unexpected underperformance (2019-2020 and 2020-2021), the participant was prospectively followed in the process of returning to sustainable world-class level (2021-2022). Day-to-day training data and physiological tests were analyzed, and interviews with the participant and the head coach conducted. Results: Longitudinal training data from 2012-2013 to 2018-2019 demonstrated a non-linear 30% increase in total training volume (from 772 to 1,002 h), mainly caused by increased volume of ski-specific endurance training without changes in intensity distribution. Coincidingly, the participant gradually reached a world-class performance level. After two seasons of unexpected underperformance with relatively similar training volumes and intensity distributions as in the preceding seasons, the possible contributing factors were identified: lack of training periodization, limited monitoring and intensity control, particularly in connection with a “extreme” regime of training with low carbohydrate availability and days including two MIT sessions, as well as lack of systematic technique training and follow-up by coaches on a daily basis. Consequently, the return to world-class level included the introduction of a clear micro-cycle periodization, more systematic physiological monitoring and testing, more accurate intensity control, increased carbohydrate intake during and between sessions, as well as increased emphasize on technique training and an assistant coach present during day-to-day training. Conclusion: These longitudinal data describe the main factors leading to unexpected underperformance, in addition to providing unique insights into the corresponding process of returning to sustainable world-class level in a male cross-country skier. The holistic approach described in this case study may serve as a theoretical framework for future studies and practical work with underperforming endurance athletes.
... Moreover, the loss of bone mineral density induced by prolonged KD intake have been proposed to be caused by bone microstructural abnormalities that promote bone absorption via activation of osteoclasts, rather than inhibition of bone formation mediated by osteoblasts [116,117]. Additionally, the KD negatively affected athletes' bone remodeling and modeling markers [118]. This section throws a beam of light on further details of the main weaknesses and harms of a KD. ...
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Insulin resistance (IR) plays a role in the pathogenesis of many diseases, such as type 2 diabetes mellitus, cardiovascular disease, non-alcoholic fatty liver disease, obesity, and neurodegenerative diseases, including Alzheimer’s disease. The ketogenic diet (KD) is a low-carbohydrate/high-fat diet that arose in the 1920s as an effective treatment for seizure control. Since then, the KD has been studied as a therapeutic approach for various IR-related disorders with successful results. To date, the use of the KD is still debatable regarding its safety. Some studies have acknowledged its usefulness, while others do not recommend its long-term implementation. In this review, we applied a SWOC (Strengths, Weaknesses, Opportunities, and Challenges) analysis that revealed the positive, constructive strengths of the KD, its potential complications, different conditions that can make used for it, and the challenges faced by both physicians and subjects throughout a KD. This SWOC analysis showed that the KD works on the pathophysiological mechanism of IR-related disorders such as chronic inflammation, oxidative stress and mitochondrial stress. Furthermore, the implementation of the KD as a potential adjuvant therapy for many diseases, including cancer, neurodegenerative disorders, polycystic ovary syndrome, and pain management was proven. On the other hand, the short and long-term possible undesirable KD-related effects, including nutritional deficiencies, growth retardation and nephrolithiasis, should be considered and strictly monitored. Conclusively, this review provides a context for decision-makers, physicians, researchers, and the general population to focus on this dietary intervention in preventing and treating diseases. Moreover, it draws the attention of scientists and physicians towards the opportunities and challenges associated with the KD that requires attention before KD initiation.
... [24] Because endurance athletes require sufficient energy to support their training, diets that reduce appetite in conjunction with decreased energy intake from acute exercise-induced anorexia may lead to LEA [25]. Other concerns with low-carbohydrate diets include the rapid reduction in markers of bone health, [26] hypercholesterolemia, [27] and nutrient deficiencies. [20] Carbohydrate restriction often coincides with general energy restriction given that the near-complete removal of carbohydrates is difficult to replace. ...
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Background Frequent dieting is common in athletes attempting to achieve a body composition perceived to improve performance. Excessive dieting may indicate disordered eating (DE) behaviors and can result in clinical eating disorders. However, the current nutrition patterns that underly dieting culture are underexplored in endurance athletes. Therefore, the purpose of this study was to identify the sex differences in nutrition patterns among a group of endurance athletes. Methods Two-hundred and thirty-one endurance athletes (females = 124) completed a questionnaire regarding their dieting patterns and associated variables. Results The majority of athletes did not follow a planned diet (70.1%). For endurance athletes on planned diets (n = 69), males were more likely follow a balanced diet ( p = 0.048) and females were more likely to follow a plant-based diet ( p = 0.021). Female endurance athletes not on a planned diet (n = 162) were more likely to have attempted at least one diet ( p < 0.001). Male athletes attempted 2.0 ± 1.3 different diets on average compared to 3.0 ± 2.0 for females ( p = 0.002). Female athletes were more likely to attempt ≥ three diets ( p = 0.022). The most common diet attempts included carbohydrate/energy restrictive, plant-based, and elimination diets. Females were more likely to attempt ketogenic ( p = 0.047), low-carbohydrate ( p = 0.002), and energy restricted diets ( p = 0.010). Females made up the entirety of those who attempted gluten-/dairy-free diets (F = 22.0%, M = 0.0%). Conclusions Being a female athlete is a major determinant of higher dieting frequency and continual implementation of popular restrictive dietary interventions. Sports dietitians and coaches should prospectively assess eating behavior and provide appropriate programming, education, and monitoring of female endurance athletes.
... As expected from traditional physiological adaptation rules, bone modeling/remodeling markers were impaired in elite endurance athletes after a 3.5-week ketogenic low-carbohydrate, high-fat diet and subsequent restoration of carbohydrate feeding. Therefore, long-term studies on bone health are warranted while adopting this diet [43]. ...
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Several studies have shown a strong correlation between the different types of diets and gut microbiota composition on glycemia and weight loss. In this direction, low-carbohydrate and ketogenic diets have gained popularity, despite studies published so far leading to controversial results on subjects with diabetes. In this narrative review, firstly, we aimed to analyze the role of very-low-calorie ketogenic diets (VLCKDs) in type 2 diabetes (T2DM) and obesity management. Secondly, in this context, we focused attention on gut microbiota as a function of VLCKD, particularly in T2DM and obesity treatment. Finally, we reported all this evidence to underline the importance of gut microbiota to exalt new nutritional strategies for “tailor-made” management, treatment, and rehabilitation in subjects with T2DM and obesity, even with diabetic complications. In conclusion, this narrative review outlined the beneficial impact of VLCKD on gut microbiota even in subjects with T2DM and obesity, and, despite inner VLCKD short-duration feature allowing no sound-enough provisions for long-term outcomes, witnessed in favor of the short-term safety of VLCKD in those patients. Level of evidence Level V: Opinions of authorities, based on descriptive studies, narrative reviews, clinical experience, or reports of expert committees.
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Low energy availability (LEA) occurs inadvertently and purposefully in many athletes across numerous sports; and well planned, supervised periods with moderate LEA can improve body composition and power to weight ratio possibly enhancing performance in some sports. LEA however has the potential to have negative effects on a multitude of physiological and psychological systems in female and male athletes. Systems such as the endocrine, cardiovascular, metabolism, reproductive, immune, mental perception, and motivation as well as behaviors can all be impacted by severe (serious and/or prolonged or chronic) LEA. Such widely diverse effects can influence the health status, training adaptation, and performance outcomes of athletes leading to both direct changes (e.g., decreased strength and endurance) as well as indirect changes (e.g., reduced training response, increased risk of injury) in performance. To date, performance implications have not been well examined relative to LEA. Therefore, the intent of this narrative review is to characterize the effects of short-, medium-, and longterm exposure to LEA on direct and indirect sports performance outcomes. In doing so we have focused both on laboratory settings as well as descriptive athletic case-study-type experiential evidence.
Background Peptide YY (PYY) is an anorexigenic gut hormone that also has anti-osteogenic effects, inhibiting osteoblastic activity and inducing catabolic effects. It has been postulated that increases in PYY after Roux-en-Y gastric bypass (RYGB) contribute to declines in bone mineral density (BMD) and increases in bone turnover. The aim of this study is to determine the role of the PYY Y2-receptor in mediating bone loss post-RYGB in mice. Methods We compared adult male wildtype (WT) and PYY Y2 receptor-deficient (KO) C57BL/6 mice that received RYGB (WT: n = 8; KO: n = 9), with sham-operated mice (Sham; WT: n = 9; KO: n = 10) and mice that were food-restricted to match the weights of the RYGB-treated group (Weight-Matched, WM; WT: n = 7; KO: n = 5). RYGB or sham surgery was performed at 15–16 weeks of age, and mice sacrificed 21 weeks later. We characterized bone microarchitecture with micro-computed tomography (μCT) at the distal femur (trabecular) and femoral midshaft (cortical). Differences in body weight, bone microarchitecture and biochemical bone markers (parathyroid hormone, PTH; C-telopeptide, CTX; and type 1 procollagen, P1NP) were compared using 2-factor ANOVA with Tukey's adjustments for multiple comparisons. Results Body weights were similar in the WT-RYGB, WT-WM, KO-RYGB, and KO-WM: 41-44 g; these groups weighed significantly less than the Sham surgery groups: 55-57 g. Trabecular BMD was 31–43 % lower in RYGB mice than either Sham or WM in WT and KO groups. This deficiency in trabecular bone was accompanied by a lower trabecular number (19 %–23 %), thickness (22 %–30 %) and increased trabecular spacing (25 %–34 %) in WT and KO groups (p < 0.001 for all comparisons vs. RYGB). RYGB led to lower cortical thickness, cortical tissue mineral density, and cortical bone area fraction as compared to Sham and WM in WT and KO groups (p ≤ 0.004 for all). There were no interactions between genotype and bone microarchitecture, with patterns of response to RYGB similar in both WT and KO groups. CTX and P1NP were significantly higher in RYGB mice than WM in WT and KO groups. PTH did not differ among groups. Conclusions RYGB induced greater trabecular and cortical deficits and high bone turnover than observed in weight-matched mice, with a similar pattern in the WT and Y2RKO mice. Thus, skeletal effects of RYGB are independent of weight loss, and furthermore, PYY signaling through Y2R is not a key mediator of bone loss post-RYGB.
Introduction: While an acute exercise session typically increases bone turnover markers (BTM), the impact of subsequent sessions and the interaction with pre-exercise calcium intake remains unclear despite the application to the 'real life' training of many competitive athletes. Methods: Using a randomized crossover design, elite male rowers (n = 16) completed two trials, a week apart, consisting of two 90-minute rowing ergometer sessions (Ex1, Ex2) separated by 150 minutes. Prior to each trial, participants consumed a high (CAL: ~1000 mg) or isocaloric low (CON: <10 mg) calcium meal. Biochemical markers including parathyroid hormone: PTH; serum ionised calcium (iCa) and bone turnover markers (C-terminal telopeptide of type I collagen: β-CTX-I; osteocalcin: OC) were monitored from baseline to 3 hours post Ex2. Results: While each session caused perturbances of serum iCa, CAL maintained calcium concentrations above those of CON for most time points, 4.5 and 2.4% higher post EX1 and EX2 respectively. The decrease in iCa in CON was associated with an elevation of blood PTH (p < 0.05) and β-CTX-I (p < 0.0001) over this period of repeated training sessions and their recovery, particularly during and after Ex2. Pre-exercise intake of calcium-rich foods lowered BTM over the course of a day with several training sessions. Conclusions: Pre-exercise intake of a calcium-rich meal prior to training sessions undertaken within the same day had a cumulative and prolonged effect on the stabilisation of blood iCa during exercise. In turn, this reduced the post-exercise PTH response, potentially attenuating the increase in markers of bone resorption. Such practical strategies may be integrated into the athlete's overall sports nutrition plan, with the potential to safeguard long term bone health and reduce the risk of bone stress injuries.
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Background Circulating biomarkers are often used to investigate the bone response to an acute bout of exercise, but heterogeneity in factors such as study design, quality, selected biomarkers, and exercise and participant characteristics render it difficult to synthesize and evaluate available evidence. Objective The aim of this study was to quantify the effects of an acute exercise bout on bone biomarkers, along with the influence of potential moderators such as participant, exercise, and design characteristics, using a systematic review and meta-analytic approach. Methods The protocol was designed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines and prospectively published. Seven databases were systematically searched in accordance with predefined eligibility criteria. Bayesian three-level hierarchical meta-analysis models were used to explore the main effects of acute exercise on bone biomarkers, as well as potential moderating factors. Modelled effect sizes were interpreted according to three metrics, namely (1) evidence of an effect (defined by whether, or how much of, the credible interval [CrI] included zero); (b) the size of that effect (threshold values of 0.01, 0.2, 0.5 and 0.8 were used to describe effect sizes as very small, small, medium and large, respectively); and (c) the level of certainty in the estimated effect (defined using the GRADE framework). Results Pooling of outcomes across all designs and categories indicated that an acute bout of exercise increased bone resorption (ES0.5 0.10, 95% CrI 0.00–0.20) and formation (ES0.5 0.05, 95% CrI 0.01–0.08) markers but the effects were very small and highly variable. Furthermore, moderator analyses revealed the source of some of this variability and indicated that exercise type and impact loading influenced the bone resorptive response. A moderate increase in C-terminal telopeptide of type 1 collagen (CTX-1) was observed in response to cycling (ES0.5 0.65, 95% CrI 0.20–0.99), with greater durations and more work leading to larger CTX-1 increases. CTX-1 response peaked within 15 min and 2 h after the exercise bout. Other exercise types did not influence CTX-1. Changes to all bone formation markers were very small and transient, with the very small increases returning to baseline within 15 min of exercise cessation. No major trends for bone formation markers were identified across any of the moderating categories investigated. Certainty of evidence in most outcomes was deemed to be low or very low. Conclusion The large influence of an acute bout of prolonged cycling on the bone resorption marker CTX-1, alongside the lack of a response of any biomarker to resistance or high-impact exercise types, indicate that these biomarkers may be more useful at investigating potentially osteolytic aspects of exercise, and raises questions about their suitability to investigate the osteogenic potential of different exercise types, at least in the short term and in response to a single exercise bout. Certainty in all outcomes was low or very low, due to factors including risk of bias, lack of non-exercise controls, inconsistency, imprecision and small-study effects. Protocol Registration and Publication This investigation was prospectively registered on the Open Science Framework Registry ( and the full protocol underwent peer review prior to conducting the investigation.
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Key points: Reduced carbohydrate (CHO) availability before and after exercise may augment endurance training-induced adaptations of human skeletal muscle, as mediated via modulation of cell signalling pathways. However, it is not known whether such responses are mediated by CHO restriction, energy restriction or a combination of both. In recovery from a twice per day training protocol where muscle glycogen concentration is maintained within 200-350 dw, we demonstrate acute post-exercise CHO and energy restriction (i.e. <24 hours) does not potentiate potent cell signalling pathways that regulate hallmark adaptations associated with endurance training. In contrast, consuming CHO before, during and after an acute training session attenuated markers of bone resorption, effects that are independent of energy availability. Whilst the enhanced muscle adaptations associated with CHO restriction may be regulated by absolute muscle glycogen concentration, the acute within day fluctuations in CHO availability inherent to twice per day training may have chronic implications for bone turnover. Abstract: We examined the effects of post-exercise carbohydrate (CHO) and energy availability (EA) on potent skeletal muscle cell signalling pathways (regulating mitochondrial biogenesis and lipid metabolism) and indicators of bone metabolism. In a repeated measures design, nine males completed a morning (AM) and afternoon (PM) high-intensity interval (HIT) (8 × 5-min at 85% VO2peak ) running protocol (interspersed by 3.5 hours) under dietary conditions of 1) high CHO availability (HCHO: CHO ∼12 , EA∼ 60 FFM), 2) reduced CHO but high fat availability (LCHF: CHO ∼3 , EA∼ 60 FFM) or 3), reduced CHO and reduced energy availability (LCAL: CHO ∼3 , EA∼ 20 FFM). Muscle glycogen was reduced to ∼200 dw in all trials immediately post PM-HIT (P < 0.01) and remained lower at 17-h (171, 194 and 316 dw) post PM-HIT in LCHF and LCAL (P < 0.001) compared to HCHO. Exercise induced comparable p38MAPK phosphorylation (P < 0.05) immediately-post PM-HIT and similar mRNA expression (all P < 0.05) of PGC-1α, p53 and CPT1 mRNA in HCHO, LCHF and LCAL. Post-exercise circulating βCTX was lower in HCHO (P < 0.05) compared to LCHF and LCAL, whereas exercise-induced increases in IL-6 were larger in LCAL (P < 0.05) compared to LCHF and HCHO. In conditions where glycogen concentration is maintained within 200-350 dw, we conclude post-exercise CHO and energy restriction (i.e. < 24 hours) does not potentiate cell signalling pathways that regulate hallmark adaptations associated with endurance training. In contrast, consuming CHO before, during and after HIT running attenuates bone resorption, effects that are independent of energy availability and circulating IL-6. This article is protected by copyright. All rights reserved.
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Purpose: Studies on long-term sustainability of low-carbohydrate approaches to treat diabetes are limited. We previously reported the effectiveness of a novel digitally-monitored continuous care intervention (CCI) including nutritional ketosis in improving weight, glycemic outcomes, lipid, and liver marker changes at 1 year. Here, we assess the effects of the CCI at 2 years.Materials and methods: An open label, non-randomized, controlled study with 262 and 87 participants with T2D were enrolled in the CCI and usual care (UC) groups, respectively. Primary outcomes were retention, glycemic control, and weight changes at 2 years. Secondary outcomes included changes in body composition, liver, cardiovascular, kidney, thyroid and inflammatory markers, diabetes medication use and disease status.Results: Reductions from baseline to 2 years in the CCI group resulting from intent-to-treat analyses included: HbA1c, fasting glucose, fasting insulin, weight, systolic blood pressure, diastolic blood pressure, triglycerides, and liver alanine transaminase, and HDL-C increased. Spine bone mineral density in the CCI group was unchanged. Use of any glycemic control medication (excluding metformin) among CCI participants declined (from 55.7 to 26.8%) including insulin (-62%) and sulfonylureas (-100%). The UC group had no changes in these parameters (except uric acid and anion gap) or diabetes medication use. There was also resolution of diabetes (reversal, 53.5%; remission, 17.6%) in the CCI group but not in UC. All the reported improvements had p < 0.00012.Conclusion: The CCI group sustained long-term beneficial effects on multiple clinical markers of diabetes and cardiometabolic health at 2 years while utilizing less medication. The intervention was also effective in the resolution of diabetes and visceral obesity with no adverse effect on bone health.Clinical Trial NCT02519309
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Purpose: The short-term restriction of carbohydrate (CHO) can potentially influence iron regulation via modification of post-exercise interleukin-6 (IL-6) and hepcidin levels. This study examined the impact of a chronic ketogenic low CHO-high fat (LCHF) diet on iron status and iron-regulatory markers in elite athletes. Methods: International-level race walkers (n=50) were allocated to one of three dietary interventions; i) a high CHO diet (HCHO; n=16), ii) periodized CHO availability (PCHO; n=17) or iii) a LCHF diet (n=17) while completing a periodized training program for 3 weeks. A 19-25 km race walking test protocol was completed at baseline and following adaptation, and changes in serum ferritin, IL-6 and hepcidin concentrations were measured. Results from HCHO and PCHO were combined into one group (CHO; n=33) for analysis. Results: The decrease in serum ferritin across the intervention period was substantially greater in the CHO group (37%) compared to the LCHF (23%) group (p=0.021). After dietary intervention, the post-exercise increase in IL-6 was greater in LCHF (13.6-fold increase; 95% CI 7.1-21.4), than athletes adhering to a CHO-rich diet (7.6-fold increase; 5.5-10.2; p=0.033). While no significant differences occurred between diets, confidence intervals indicate 3 h post-exercise hepcidin concentrations were lower after dietary intervention compared to baseline in CHO (β=-4.3; -6.6, -2.0), with no differences evident in LCHF. Conclusion: Athletes who adhered to a CHO-rich diet experienced favorable changes to the post-exercise IL-6 and hepcidin response, relative to the LCHF group. Lower serum ferritin after 3 weeks of additional dietary CHO might reflect a larger more adaptive hematological response to training.
Purpose: We investigated the effect of a 31-d ketogenic diet (KD) on submaximal exercise capacity and efficiency. Methods: A repeated-measures, crossover study with preintervention and postintervention outcomes was conducted in eight trained male endurance athletes (maximal oxygen uptake (V[Combining Dot Above]O2max), 59.4 ± 5.2 mL⋅kg⋅min). Participants ingested their habitual diet (HD) (43% ± 8% carbohydrate and 38% ± 7% fat) or an isoenergetic KD (4% ± 1% carbohydrate and 78% ± 4% fat) from days 0 to 31 (P < 0.001). On days -2 and 29, participants undertook a fasted graded metabolic test (~25 min), and on days 0 and 31, participants completed a run-to-exhaustion trial at 70% of their V[Combining Dot Above]O2max (~12.9 km⋅h) after the ingestion of a high-carbohydrate meal (2 g⋅kg) or an isoenergetic low-carbohydrate, high-fat meal, with carbohydrate (~55 g⋅h) or isoenergetic fat (coconut oil) supplementation during exercise. Results: Training load did not differ between trials, and there was no effect of diet on V[Combining Dot Above]O2max (all, P > 0.05). The KD impaired exercise efficiency, particularly at >70% V[Combining Dot Above]O2max, as evident by oxygen uptake that could not be explained by shifts in RER and increased energy expenditure (all, P < 0.05). However, exercise efficiency was maintained on a KD when exercising at <60% V[Combining Dot Above]O2max (all, P > 0.05). There was no effect of diet on time-to-exhaustion (237 ± 44 min (pre-HD) vs 231 ± 35 min (post-HD), P = 0.44; 239 ± 27 min (pre-KD) vs 219 ± 53 min (post-KD), P = 0.36). Conclusion: A 31-d KD can preserve submaximal exercise capacity in trained endurance athletes; however, endurance variability increases.
We describe the implementation of a 3-week dietary intervention in elite race walkers at the Australian Institute of Sport, with a focus on the resources and strategies needed to accomplish a complex study of this scale. Interventions involved: traditional guidelines of high carbohydrate (CHO) availability for all training sessions (HCHO); a periodized CHO diet which integrated sessions with low CHO and high CHO availability within the same total CHO intake, and a ketogenic low-CHO high-fat diet (LCHF). 7-day menus and recipes were constructed for a communal eating setting to meet nutritional goals as well as individualized food preferences and special needs. Menus also included nutrition support pre, during and post-exercise. Daily monitoring, via observation and food checklists, showed that energy and macronutrient targets were achieved: diets were matched for energy (~14.8 MJ/d) and protein (~2.1, and achieved desired differences for fat and CHO: HCHO and PCHO: CHO = 8.5 g/kg/d, 60% energy; fat = 20% of energy; LCHF: 0.5 g/kg/d CHO, fat = 78% energy. There were no differences in micronutrient intakes or density between HCHO and PCHO diets; however, the micronutrient density of LCHF was significantly lower. Daily food costs per athlete were similar for each diet (~AUDS$27 ± 10). Successful implementation and monitoring of dietary interventions in sports nutrition research of the scale of the present study require meticulous planning and the expertise of chefs and sports dietitians. Different approaches to sports nutrition support raise practical challenges around cost, micronutrient density, accommodation of special needs and sustainability.
Background: The short-term effects of low energy availability (EA) on bone metabolism in physically active women and men are currently unknown. Purpose: We evaluated the effects of low EA on bone turnover markers (BTMs) in a cohort of women and a cohort of men, and compared effects between sexes. Methods: These studies were performed using a randomised, counterbalanced, crossover design. Eleven eumenorrheic women and eleven men completed two 5-day protocols of controlled (CON; 45kcal·kgLBM-1·d-1) and restricted (RES; 15kcal·kgLBM-1·d-1) EAs. Participants ran daily on a treadmill at 70% of their peak aerobic capacity (VO2 peak) resulting in an exercise energy expenditure of 15kcal·kgLBM-1·d-1 and consumed diets providing 60 and 30kcal·kgLBM-1·d-1. Blood was analysed for BTMs [β-carboxyl-terminal cross-linked telopeptide of type I collagen (β-CTX) and amino-terminal propeptide of type 1 procollagen (P1NP)], markers of calcium metabolism [parathyroid hormone (PTH), albumin-adjusted calcium (ACa), magnesium (Mg) and phosphate (PO4)] and regulatory hormones [sclerostin, insulin-like growth factor 1 (IGF-1), triiodothyronine (T3), insulin, leptin, glucagon-like-peptide-2 (GLP-2)]. Results: In women, β-CTX AUC was significantly higher (P=0.03) and P1NP AUC was significantly lower (P=0.01) in RES compared to CON. In men, neither β-CTX (P=0.46) nor P1NP (P=0.12) AUCs were significantly different between CON and RES. There were no significant differences between sexes for any BTM AUCs (all P values>0.05). Insulin and leptin AUCs were significantly lower following RES in women only (for both P=0.01). There were no differences in any AUCs of regulatory hormones or markers of calcium metabolism between men and women following RES (all P values>0.05). Conclusions: When comparing within groups, five days of low EA (15kcal·kgLBM-1·d-1) decreased bone formation and increased bone resorption in women, but not in men, and no sex specific differences were detected.
The ketogenic diet (KD) is a medically supervised, high fat, low carbohydrate and restricted protein diet which has been used successfully in patients with refractory epilepsy. Only one published report has explored its effect on the skeleton. We postulated that the KD impairs skeletal health parameters in patients on the KD. Patients commenced on the KD were enrolled in a prospective, longitudinal study, with monitoring of Dual-energy X-ray absorptiometry (DXA) derived bone parameters including bone mineral content and density (BMD). Areal BMD was converted to bone mineral apparent density (BMAD) where possible. Biochemical parameters, including Vitamin D, and bone turnover markers, including osteocalcin, were assessed. Patients were stratified for level of mobility using the gross motor functional classification system (GMFCS). 29 patients were on the KD for a minimum of 6 months (range 0.5-6.5 years, mean 2.1 years). There was a trend towards a reduction in lumbar spine (LS) BMD Z score of 0.1562 (p = 0.071) per year and 20 patients (68%) had a lower BMD Z score at the end of treatment. While less mobile patients had lower baseline Z scores, the rate of bone loss on the diet was greater in the more mobile patients (0.28 SD loss per year, p = 0.026). Height adjustment of DXA data was possible for 13 patients, with a mean reduction in BMAD Z score of 0.19 SD. Only two patients sustained fractures. Mean urinary calcium-creatinine ratios were elevated (0.77), but only 1 patient developed renal calculi. Children on the KD exhibited differences in skeletal development that may be related to the diet. The changes were independent of height but appear to be exaggerated in patients who are ambulant. Clinicians should be aware of potential skeletal side effects and monitor bone health during KD treatment. Longer term follow up is required to determine adult/peak bone mass and fracture risk throughout life.