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MS IDA LYSDAHL FAHRENHOLTZ (Orcid ID : 0000-0003-1147-0924)
Article type : Original Article
TITLE: WITHIN-DAY ENERGY DEFICIENCY AND REPRODUCTIVE FUNCTION IN
FEMALE ENDURANCE ATHLETES
AUTHORS: Fahrenholtz I.L.1, Sjödin A.1, Benardot D.3, Tornberg Å.B.2, Skouby S.4, Faber J.5,
Sundgot-Borgen J.6, Melin A1.
1Department of Nutrition, Exercise and Sports, University of Copenhagen, Frederiksberg,
Denmark; 2Department of Health Sciences, Lund University, Lund, Sweden, 3Department of
Nutrition, Georgia State University, Atlanta, GA; 4Endocrinological and Reproductive Unit,
Department of Obstetrics/Gynecology, Herlev Hospital, Faculty of Health and Medical Sciences,
University of Copenhagen, Herlev, Denmark; 5Medical and Endocrinological Unit, Herlev
Hospital, Faculty of Health and Medical Sciences, University of Copenhagen, Herlev, Denmark;
6Norwegian School of Sport Sciences, Oslo, Norway.
CORRESPONDING AUTHOR:
Anna Katarina Melin: Copenhagen University, Department of Nutrition Exercise and Sports,
Rolighedsvej 26, 1958 Frederiksberg, Denmark. E-mail: aot@nexs.ku.dk. Tlf: +46732629714
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RUNNING HEAD: Within-day energy deficiency
ABSTRACT
We aimed to estimate and compare within-day energy balance (WDEB) in athletes with
eumenorrhea and menstrual dysfunction (MD) with similar 24-hour energy availability/energy
balance (EA/EB). Furthermore, to investigate whether within-day energy deficiency is associated
with resting metabolic rate (RMR), body-composition, S-cortisol, estradiol, T3, and fasting blood
glucose. We reanalyzed 7-day dietary intake and energy expenditure data in 25 elite endurance
athletes with eumenorrhea (n=10) and MD (n=15) from a group of 45 subjects where those with
disordered eating behaviors (n=11), MD not related to low EA (n=5), and low dietary record
validity (n=4) had been excluded. Besides gynecological examination and disordered eating-
evaluation, the protocol included RMR-measurement; assessment of body-composition by dual-
energy X-ray absorptiometry, blood plasma analysis, and calculation of WDEB in 1-hour
intervals. Subjects with MD spent more hours in a catabolic state compared to eumenorrheic
athletes; WDEB <0 kcal: 23.0 hour (20.8–23.4) vs 21.1 hour (4.7–22.3), P=0.048; WDEB <-300
kcal: 21.8 hour (17.8–22.4) vs 17.6 hour (3.9–20.9), P=0.043, although similar 24-hour EA: 35.6
(11.6) vs 41.3 (12.7) kcal/kg FFM/day, (P=0.269), and EB: -659 (551) vs -313 (596) kcal/day,
(P=0.160). Hours with WDEB <0 kcal and <-300 kcal were inversely associated with RMRratio
(r=-0.487, P=0.013, r=-0.472, P=0.018), and estradiol (r=-0.433, P=0.034, r=-0.516, P=0.009),
and positively associated with cortisol (r=0.442, P=0.027, r=0.463, P=0.019). In conclusion,
although similar 24-hour EA/EB, the reanalysis revealed that MD athletes spent more time in a
catabolic state compared to eumenorrheic athletes. Within-day energy deficiency was associated
with clinical markers of metabolic disturbances.
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KEY WORDS: Energy availability, within-day energy balance, relative energy deficiency,
amenorrhea, catabolism, RMR.
INTRODUCTION
Athletes need an adequate and balanced food and fluid intake that provides nutritional support
for optimal adaption to training and optimal performance, but also for preventing illness and
injuries. An appropriate energy intake is the cornerstone of the athlete’s diet because it supports
optimal body function, determines the capacity for intake of macronutrient and micronutrients,
and assists in manipulating body composition1,2. Female athletes focusing on leanness, however,
have been reported to have an increased risk of developing restricted eating behaviors and low
energy availability (EA)3,4,5. Low EA with or without disordered eating (DE) behavior is related
to endocrine alterations leading to several health and performance impairing conditions including
menstrual dysfunction (MD), gastrointestinal problems, impaired bone health, and increased
injury risk4,5,6 . The hormonal synthesis and increased luteal phase thermogenesis are energy
consuming processes7, and the energy metabolism at rest (RMR) therefore changes up to 10%
during the menstrual cycle, with peaks during the late luteal phase or the early follicular phase8.
MD may consequently result in lower energy needs in a physiological adaptation to insufficient
energy intakes. Most female athletes with long-term energy deficiency are reported to maintain a
steady body weight and body composition within the normal range, independent of their
reproductive function9. Therefore, other metabolic mechanisms may be involved, such as a
reduction in RMR and/or non-exercise activity thermogenesis (NEAT)10, as well as in increased
work-load efficiency11,12.
Traditionally, the energy status of athletes is evaluated in blocks of 24-hours as either energy
balance (EB) (energy intake – total energy expenditure) or EA (energy intake – exercise energy
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expenditure)13. Experimental studies have demonstrated a causal relationship between low EA
and the endocrine perturbations related to MD14,15,16. However, consistent with many other
studies6,17,18 we have previously reported similar 24-hour EA and EB in this group of elite
athletes with MD vs eumenorrheic athletes12,19.
The traditional 24-hour view on human thermodynamics has been criticized for failing to
account for the endocrine responses that act on real-time changes in energy intake and
expenditure20. Therefore, a new view on EB, where energy intake and energy expenditure are
assessed in 1-hour intervals, has been proposed to be more appropriate20. Within-day energy
deficiency (WDED) has previously been associated with an unfavorable body composition in
female elite gymnasts and runners, presumably related to both an adaptive reduction in RMR21,
and endocrine responses that favor muscle catabolism and fat gain20,21. Therefore, a restrictive
eating behavior, resulting in more hours spent in energy deficiency, may have the opposite of the
desired effect on athletes’ body composition. A desirable range of EB of ± 300 kcal has been
suggested, since 300 kcal corresponds to the predicted amount of liver glycogen for female
athletes21. Exceeding the threshold of EB below -300 kcal, could potentially accelerate
biochemical pathways associated with energy deficiency20 and compromise brain glucose
availability and thereby normal gonadotropin-releasing hormone (GnRH) neuron activity and
luteinizing hormone (LH) pulsatility7,13.
According to the International Olympic Committee consensus statement, WDED is a possible
contributor to the reproductive and metabolic alterations associated with relative energy
deficiency4. However, these links have not been demonstrated in athletes. Hence, we wanted to
investigate if female elite endurance athletes with MD with similar reported 24-hour EB and EA
as eumenorrheic athletes spend more time in a catabolic state and have a larger magnitude of
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WDED compared to eumenorrheic athletes. Furthermore, it was our intent to investigate if
WDED is associated with suppressed RMR and endocrine alterations in these athletes.
METHODS
Permission to undertake the study was provided by the Swedish and Danish Confederation of
Sports, Team Denmark, the Data Inspectorate, and the Regional Ethical committees, both in
Sweden and Denmark (nos. 2011/576 and H-4-2011-096, respectively). The protocol was
registered at www.clinicaltrials.gov.
We reanalyzed data concerning 7-day energy intake and energy expenditure from a previous
study19, and the recruitment and methods used have previously been described in detail12.
Athletes recruited and included in the subject pool were endurance athletes on a national team or
competitive club level between the age of 18 to 38 years, and training a minimum of 5 times per
week. All subjects had been informed orally, and in writing, of all study procedures and signed
an informed consent form. Data were collected on 2 consecutive days that were followed by a 7-
day recording period in the athletes’ normal environment. The timing of the examination and
registration period was planned individually for each subject to choose a period that reflects their
habitual food habits and exercise regimes. Menstruating athletes were examined in the early
follicular phase.
The first day consisted of anthropometric assessment [body weight and height, dual-energy X-
ray absorptiometry (DXA) to determine fat free mass (FFM) and fat mass (FM)], and
examinations of reproductive function (a transvaginal ultrasound examination by an experienced
gynecologist, sex hormone status, and a retrospective menstrual history using LEAF-Q22).
Subjects were classified with eumenorrhea (menstrual cycles of 28 days ±7 days and sex
hormones within the normal range), functional hypothalamic oligomenorrhea (menstrual cycles
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>35 days where other causes than hypothalamic suppression had been ruled out), amenorrhea
(either primary: no menarche after 15 years of age, or secondary: absence of at least 3
consecutive menstrual cycles where other causes than hypothalamic suppression had been ruled
out), or other MD not related to energy deficiency. The second day included examinations of
aerobic capacity and assessment of DE assessed by the Eating Disorder Inventory23. The
incremental test reflected heart rates being linearly correlated with O2 consumption at increasing
workloads (r = 0.94, 95% CI 0.93-0.96), providing the basis for the individual regression lines
and later calculations of exercise-associated energy expenditure. RMR was assessed after an
overnight fast, using a ventilated open hood system (Oxycon Pro 4, Jeager, Germany). Blood
was drawn from an antecubital vein in fasted subjects between 8:30 and 8:50 by a qualified bio-
technician12.
After the 2 examination days, subjects weighed and registered food and beverage intake during a
consecutive 7-day period using a digital kitchen scale (Exido 246030 Kitchen Scale, Gothenburg,
Sweden). Heart rate monitors (Polar RS400®,Kempele, Finland) and training logs were used to
assess energy expenditure during exercise and bicycle transportation, while subjects wore an
accelerometer (ActiGraph GT3X®, Pensacola, FL, USA) on the hip (except during showering,
swimming, bicycle transportation, and training) for the assessment of NEAT. Exercise energy
expenditure for swim sessions was calculated based on mean heart rate obtained from the
remaining training sessions. NEAT was calculated for each waking hour using the data analysis
software ActiLife 6 (ActiGraph). The nutrient analysis program MadlogVita (Madlog ApS,
Kolding, Denmark) and Dietist XP (Kost och Näringsdata AB, Bromma, Sweden) were used to
analyze food records. The daily numbers of meals and snacks were counted. Dietary analysis was
performed in 25 subjects after excluding 5 due to clinically verified MD other than functional
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hypothalamic amenorrhea/oligomenorrhea, 11 due to DE, and 4 due to low validity using the
equation described by Black24.
EA was calculated as total energy intake minus exercise energy expenditure (mean/24hour)
expressed in relation to FFM. The athletes themselves defined and registered every training
session.
The hourly within-day energy balance (WDEB) was calculated as follows: energy intake – total
energy expenditure, where total energy expenditure represents exercise energy expenditure +
predicted exercise post oxygen consumption (EPOC) + diet induced thermogenesis (DIT) +
NEAT + RMR. WDED variables were used according to Deutz, et al.21: total hours with energy
deficit (unadapted WDEB < 0 kcal), hours spent in energy deficit exceeding 300 kcal (unadapted
WDEB < -300 kcal), and largest single-hour energy deficit (Figure 1). DIT was defined as 10%
of energy intake and the equation 175.9·T·e -T/1.3 presented by Reed and Hill25 was used to
calculate DIT the first 6 hours after each meal/snack. Based on results from studying young
active eumenorrheic women26, EPOC was calculated as 5% of exercise energy expenditure the
first hour post-exercise plus 3% of exercise energy expenditure the second hour post-exercise.In
order to control for the problem of potential underestimation of energy requirements, the
unadapted/predicted RMR, instead of measured RMR, was used when calculating total energy
expenditure. Hence, the aim was to calculate the unadapted EB. The hourly predicted RMR was
calculated using the Cunningham equation: RMR, kcal/hour = (500 + (22· FFM [kg])
kcal/day)/24 hours/day. The RMRratio was calculated as measured RMR/predicted RMR.
Sleeping metabolic rate was calculated as 90% of RMR and used instead of RMR during
sleeping hours. The starting point for the calculation of WDEB was at midnight on the first day
of food recording and was calculated as the mean energy intake of the last daily meal or snack
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minus mean total energy expenditure in the time interval following the mean meal/snack
consumption. WDEB was calculated continuously for the 7 days of registration.
Statistics
Statistical calculations were performed using RStudioTM (version 0.99.879) with a two-tailed
significance level of < 0.05. All data sets were tested for normality and homogeneity of variance
before statistical hypothesis tests were performed. Normally distributed data were summarized as
mean and standard deviation (SD), and non-normally distributed data as median and interquartile
range (IQ 25 and IQ 75 percentiles). Differences between MD and eumenorrheic subjects were
investigated using unpaired Student’s t-test for normally distributed data and the Wilcoxon rank-
sum test for non-parametric data. Pearson’s correlation coefficient and Spearman’s rank
correlation coefficient were calculated to investigate associations between WDED variables and
continuous outcomes for normally and non-normally distributed data, respectively.
RESULTS
Subject characteristics are presented in Table 1. As earlier reported19 15 of 25 subjects (60%)
were diagnosed with MD and there were no differences in age, height, body weight or BMI
between subjects characterized by reproductive function. MD subjects had 19% lower FM and
14% lower relative FM compared to eumenorrheic subjects, although there were no differences
in training volume or exercise capacity.
There were no differences in any of the energy expenditure components between eumenorrheic
and MD subjects, but subjects with MD had lower RMRratio compared to eumenorrheic subjects
(Table 2).
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There was no difference in 24-hour EA [35.6 (11.6) vs 41.3 (12.7) kcal/kg FFM/day, P = 0.269)]
or EB [-659 (551) vs -313 (596) kcal/day, P = 0.160] between subjects with MD vs those with
eumenorrhea. Subjects with MD spent more time with EB < 0 kcal (P = 0.048) and < -300 kcal
(P = 0.043) compared to eumenorrheic subjects (Table 3). Subjects with MD had significantly
more meals/snacks per day compared to eumenorrheic subjects [6.5 (1.0) vs 5.5 (0.8) meals/day,
P = 0.014]. We found no association between meal frequency and energy intake, but time spent
in energy deficiency was positively associated with meal frequency (r = 0.398, P = 0.0485).
A sub analysis excluding oligomenorrheic subjects, showed a more pronounced difference
between amenorrheic (n = 11) and eumenorrheic subjects in EB < 0kcal [23.3 (22.7 – 23.6) hours
vs 21.1 (4.7 – 22.3) hours, (P = 0.009)] and < -300 kcal [22.3 (21.6 – 22.7) hours vs 17.6 (3.9 –
20.9) hours (P = 0.007)].
The regression analysis showed that the more hours spent with EB < 0 kcal and < -300 kcal, the
lower the RMRratio and estrogen and the higher the cortisol levels (Table 4). In addition, smaller
magnitudes of hourly energy deficits (closer to 0 kcal) were associated with higher estrogen
level.
DISCUSSION
Although assessed athletes had similar 24-hour EA and EB, this reanalysis revealed that those
with MD spent significantly more time in a catabolic state compared to eumenorrheic athletes. In
addition, the more time the athletes spent in a catabolic state the lower the RMRratio and estrogen,
and the higher the cortisol levels.
Previously, Deutz and colleges21 investigated WDEB in female elite athletes. The present study
is, however, the first to include its relationship with reproductive function and metabolic
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adaptations. In contrast to Deutz and collaborators, we found no association between WDED and
body composition.
The menstrual cycle is an energy demanding process that relies on adequate availability of
energy and glucose for optimal LH pulsatility13. Randomized controlled trials have demonstrated
a disruption of the normal sex hormone secretion in regularly menstruating women14,15,16 when
manipulating EA, and it is well established that relative energy deficiency increases the risk of
MD4. However, in line with many earlier studies6,17,18 we could not demonstrate significant
differences in 24-hour EB or EA between MD and eumenorrheic athletes. Several researchers
have suggested that a plausible difference among women is their susceptibility to energy
restriction3,17,18,19,27, which might contribute to the explanation for similar 24-hour EB and EA in
athletes with and without MD. An additional factor could be that the 24-hour assessment of
energy status masks periods with energy deficiency substantial enough to maintain reproductive
dysfunction. When calculating the traditional 24-hour EB or EA light training days may have a
compensatory effect on the mean 24-hour value. In contrast, the WDEB calculation is
cumulative and takes into account potential energy deficiencies or access from previous days.
During the follicular phase, pulses of GnRH, responsible of the release of LH and follicle
stimulating hormone from the anterior pituitary, occur at hourly intervals7, and animal studies
suggest that the reproductive function is responsive to hourly changes in metabolic fuel
oxidation28. Both energy expenditure and energy intake fluctuate greatly during waking hours,
providing a natural within-day variation in EA and EB in athletes13. Although the athletes in the
present study, independently of reproductive function, spent the majority of the day in an energy
deficient state, the athletes with MD spent 24% more hours in EB < -300 kcal compared to
eumenorrheic athletes, providing a potentially more profound catabolic state in female athletes
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with MD. It is possible that amenorrheic athletes spend a greater proportion of time during the
day without sufficient blood glucose available, which would negatively impact normal
functioning of the hypothalamic-pituitary-gonadal-axis. There was however, no difference in the
largest hourly deficit between groups, which may indicate that large energy deficit if transient do
not disturb reproductive function. The large variations within the eumenorrhea group illustrate
that some athletes classified with regular menstrual cycles also had prolonged deficits. Loucks
and Thuma15 demonstrated that women with shorter luteal phase (11 days) are more susceptible
to energy deficiency in terms of endocrine alterations compared to women with longer luteal
phases (12-14 days). As discussed by the authors, women that by nature have a slightly shorter
luteal phase may be of an increased risk of developing MD when exposed to energy deficiency15.
Thus, the eumenorrheic athletes with a high number of catabolic hours in the present study may
be women with a more robust reproductive function. On the other hand, it is unknown whether
these athletes may have had subclinical MDs associated with energy deficiency such as
anovulation or luteal phase abnormality (luteal length < 10 days or inadequate/low progesterone
concentration6). This condition is diagnosed by measuring daily ovarian steroid hormones in
blood or urine over a full menstrual cycle9. Indeed, an incidence of 79% of luteal phase
deficiency has been reported among recreational, regularly menstruating runners in a 3-months
sample6. In the sedentary control group, 90% of all menstrual cycles were ovulatory, whereas in
the runners only 45% were ovulatory. Another possible explanation is related to the cross-
sectional design where measurements only provide a snapshot over one week and not necessarily
the long-term consequences of energy deficiency, which is necessary to develop MD. In this
perspective, it is important also to evaluate more acute consequences of energy deficiency such
as suppressed RMR as we did in the present study, where we found WDED to be associated with
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lower RMRratio. Several studies have reported reduced RMR in female athletes with MD
compared to eumenorrheic athletes12,29,30,31, and our results support previous studies suggesting
that the RMRratio may be used as a useful marker for identifying athletes with energy
deficiency5,12,18,27. Consequently, when calculating EB in athletes with insufficient energy intake
and MD, using measured RMR might result in a more neutral EB, underestimating the degree of
energy deficiency13,32.
We found WDED to be associated with higher cortisol and lower estrogen levels and a trend
suggesting lower T3 levels, as signs of biological stress. LH pulsatility, T3 and cortisol levels are
regulated by brain glucose availability13 hence extensive periods in an energy deficient state are
likely to cause these hormonal alterations.
The present study found no association between body composition and WDED. This is in
contrast to an earlier study assessing elite female runners and gymnasts, where hours with EB <
0 kcal, and with EB < -300 kcal were positively associated with relative fat mass (r = 0.285, P =
0.03 and r = 0.407, P < 0.01, respectively), and the largest energy deficit was negatively
associated with relative fat mass (r = -0.378, P < 0.01)21. It has been suggested that an increased
meal frequency33, and an increased protein intake of 1.8–2.0 g/kg/day34 during hypocaloric
conditions might have an anti-catabolic effect on FFM in athletes. Hence, the high meal
frequency and high protein intake [2.1 (0.4) g/kg/day]19 observed among these MD athletes
might potentially explain the maintenance of FFM despite profound WDED.
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Limitations
Since this is an observational study, it is not able to demonstrate a causal relationship between
WDED and reproductive function or metabolic adaptations. As reviewed by Burke1, studies
using self-reported food diaries are always challenged by errors of validity and reliability.
Although subjects with DE behavior and suspected under reporters were excluded, there is a risk
for not identifying all subjects miss-reporting dietary intake24. Despite possible systemic errors,
these are presumed to be equally distributed between groups and the differences found are
therefore still valid even if energy expenditure has been overestimated and/or energy intake has
been underestimated. Due to the small sample size and several correlation analyses made, our
results should primarily be seen exploratory. Nevertheless, our findings that MD athletes spent
significantly more time in a catabolic state compared to eumenorrheic athletes although similar
24-hour EA and EB assessment is interesting and was associated with clinical markers of energy
suppression e.g. lower RMR. Finally, the energy deficiency cut-off -300 kcal, suggested by
Deutz, et al.21, is theoretically founded and may vary depending on different individual factors,
including body weight35. Lack of identification of subclinical MD are also a limitation of the
study. As other calculation methods evaluating athletes’ energy status, the WDEB calculation
entails uncertainties. Nevertheless, the 24-hour assessments, although more practical, may be too
simple to detect the differences in energy deficiency between MD and eumenorrheic athletes.
Practical implications
Based on the results from the present and other studies6,17,18, a continuous view on energy status
evaluated in smaller time blocks may be more appropriate than the 24-hour assessments.
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However, the method is time-consuming and requires equipment capable of assessing energy
expenditure in minor blocks, and participants must carefully note the timing of energy intake and
energy expenditure. Nonetheless, our results emphasize important considerations for
practitioners of the potential limitations of the 24-hour assessment. A high meal frequency may
be necessary for athletes to ensure adequate energy intake35,36 and to improve WDEB. However,
the paradoxical finding of a positive association between WDED and meal frequency, suggests
that a high meal frequency does not improve WDEB in athletes eating mainly low energy dense
foods as earlier reported in this population, especially among MD athletes19. Therefore, other
dietary characteristics, behavioral attitudes and taboos towards certain foods, including
carbohydrate-rich foods, fats, and energy containing beverages needs to be evaluated when
counseling athletes at risk for energy deficiency.
Perspectives
The present study demonstrates that the traditional 24-hour assessment of EB and EA may not be
sufficient for detecting athletes in an energy deficient state and a continuous view on EB may be
more appropriate. This is the first study to investigate the relationship between WDED and
clinically verified MD as well as metabolic suppression related to energy deficiency. Therefore,
more studies are needed, preferably with larger sample size in order to be able to differentiate
between subjects with oligomenorrhea and amenorrhea, but also subjects with subclinical MD
(anovulation and short luteal phase defect).
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ACKNOWLEDGMENTS
We thank Drs Mubeena Aziz and Katrine Haahr at Herlev Hospital for performing gynecological
examinations; Anders Johansson, Lund University, and Ulla Kjærulff-Hansen, Herlev Hospital,
for assisting with blood sampling; Fiona Koivola, Lund University, for assisting during testing,
and Hanne Udengaard, Herlev Hospital, for logistics assistance. Finally, we highly appreciate the
extraordinary cooperation of the athletes participating in this study and the support of the
Swedish and Danish national sports federations and Team Denmark.
Funding
This study was funded by research grants from the Faculty of Science, University of
Copenhagen, World Village of Women Sports Foundation and Arla Foods Ingredients.
CONFLICTS OF INTEREST
The results of the present study are presented clearly, honestly, and without fabrication,
falsification, or inappropriate data manipulation. Dan Benardot is the inventor and scientific
advisor of NutriTiming®, a software package that analyzes hourly EB. This software program,
however, was not used for this study.
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REFERENCES
1. Burke LM. Energy needs of athletes. Can J Appl Physiol. 2001;26:S202-19.
2. Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and
Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition
and Athletic Performance. J Acad Nutr Diet. 2016;116:501-28.
3. Manore MM. Dietary recommendations and athletic menstrual dysfunction. J Sports Sci.
2002;32:887-901.
4. Mountjoy M, Sundgot-Borgen J, Burke L, et al. The IOC consensus statement: beyond
the Female Athlete Triad – Relative Energy Deficiency in Sport (RED-S). Brit J Sports
Med. 2014;48:491-7.
5. Nattiv A, Loucks AB, Manore M, Sanborn CF, Sundgot-Borgen J, Warren MP. The
female athlete triad. Med Sci Sports Exer. 2007;39:1867-82.
6. De Souza MJ, Miller BE, Loucks AB, et al. High Frequency of Luteal Phase Deficiency
and Anovulation in Recreational Women Runners: Blunted Elevation in Follicle-
Stimulating Hormone Observed during Luteal-Follicular Transition 1. J Clin Endocrinol
Metab. 1998;83:4220-32.
7. Harber VJ. Energy balance and reproductive function in active women. Can J Appl
Physiol. 2004;29:48-58.
8. Henry CJK, Lightowler HJ, Marchini J. Intra-individual variation in resting metabolic
rate during the menstrual cycle. Br J Nutr. 2003;89:811-17.
9. Redman LM, Loucks AB. Menstrual disorders in athletes. Sports Med. 2005;35:747-55.
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This article is protected by copyright. All rights reserved.
10. Redman LM, Heilbronn LK, Martin CK, et al. Metabolic and behavioral compensations
in response to caloric restriction: implications for the maintenance of weight loss. PloS
One. 2009;4:e4377.
11. Goldsmith R, Joanisse DR, Gallagher D, et al. Effects of experimental weight
perturbation on skeletal muscle work efficiency, fuel utilization, and biochemistry in
human subjects. Am J Physiol Regul Integr Comp Physiol. 2010;298:R79-88.
12. Melin A, Tornberg ÅB, Skouby S, et al. Energy availability and the female athlete triad
in elite endurance athletes, Scand J Med Sci Sports. 2014;25:610-22.
13. Loucks AB. Energy balance and energy availability. In: Maughan, RJ, editor. The
Encyclopedia of Sports Medicine, Energy and Macronutrients. International Olympic
Committee. 1 ed. John Wiley & Sons, Ltd; 2014. p. 72-87.
14. Loucks AB, Heath EM. Dietary restriction reduces luteinizing hormone (LH) pulse
frequency during waking hours and increases LH pulse amplitude during sleep in young
menstruating women. J Clin Endocrinol Metab. 1994;78:910-15.
15. Loucks AB, Thuma JR. Luteinizing hormone pulsatility is disrupted at a threshold of
energy availability in regularly menstruating women. J Clin Endocrinol Metab.
2003;88:297-311.
16. Olson BR, Cartledge T, Sebring N, Defensor R, Nieman L. Short-term fasting affects
luteinizing hormone secretory dynamics but not reproductive function in normal-weight
sedentary women. J Clin Endocrinol Metab. 1995;80:1187-93.
17. Guebels CP, Kam LC, Maddalozzo GF, Manore MM. Active women before/after an
intervention designed to restore menstrual function: Resting metabolic rate and
Accepted Article
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comparison of four methods to quantify energy expenditure and energy availability. Int J
Sport Nutr Exerc Metab. 2014;24:37-46.
18. Schaal K, Van Loan MD, Casazza GA. Reduced Catecholamine Response to Exercise in
Amenorrheic Athletes. Med Sci Sports Exerc. 2001;43:34-43.
19. Melin A, Tornberg ÅB, Skouby S, et al. Low‐energy density and high fiber intake are
dietary concerns in female endurance athletes. Scand J Med Sci Sports. 2015;26:1060-71.
20. Benardot D. Energy Thermodynamics Revisited: Energy intake strategies for optimizing
athlete body composition and performance. Pensar en Movimiento. 2013;11:1-13.
21. Deutz RC, Benardot D, Martin DE, Cody MM. Relationship between energy deficits and
body composition in elite female gymnasts and runners. Med Sci Sport Exerc.
2000;32:659-68.
22. Melin A, Tornberg ÅB, Skouby S, et al. The LEAF questionnaire: a screening tool for the
identification of female athletes at risk for the female athlete triad, Brit J Sports Med.
2014;48:540-5.
23. Garner DM. Eating Disorder Inventory-3. Professional Manual. Par. Inc. 2004. p. 1-213.
24. Black AE. Critical evaluation of energy intake using the Goldberg cut-off for energy
intake: basal metabolic rate. A practical guide to its calculation, use and limitations. Int J
Obes Relat Metab Disord. 2000;24:1119-30.
25. Reed GW, Hill JO. Measuring the thermic effect of food. Am J Clin Nutr. 1996;63:164-9.
26. Phelain JF, Reinke E, Harris MA, Melby CL. Postexercise energy expenditure and
substrate oxidation in young women resulting from exercise bouts of different intensity. J
Am Coll Nutr. 1997;16:140-6.
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27. Gibbs JC, Williams NI, Scheid JL, Toombs RJ, De Souza MJ. The association of a high
drive for thinness with energy deficiency and severe menstrual disturbances:
confirmation in a large population of exercising women. Int J Sport Nutr Exerc Metab.
2011;21:280-90.
28. Wade GN, Jones JE. Neuroendocrinology of nutritional infertility. Am J Physiol Regul
Integr Comp Physiol. 2004;287:R1277-96.
29. O'Donnell E, Harvey PJ, De Souza MJ. Relationships between vascular resistance and
energy deficiency, nutritional status and oxidative stress in oestrogen deficient physically
active women. Clin Endocrinol. 2009;70: 294-302.
30. Scheid JL, Williams NI, West SL, VanHeest JL, De Souza MJ. Elevated PYY is
associated with energy deficiency and indices of subclinical disordered eating in
exercising women with hypothalamic amenorrhea. Appetite. 2009;52:184-192.
31. Vanheest JL, Rodgers CD, Mahoney CE, De Souza MJ. Ovarian suppression impairs
sport performance in junior elite female swimmers. Med Sci Sports Exerc. 2014;46:156-
66.
32. Loucks AB, Kiens B, Wright HH. Energy availability in athletes. J Sports Sci.
2011;29:S7-15.
33. Iwao S, Mori K, Sato Y. Effects of meal frequency on body composition during weight
control in boxers. Scand J Med Sci Sports. 1996;6:265-72.
34. Phillips SM, Van Loon LJ. Dietary protein for athletes: from requirements to optimum
adaptation. J Sports Sci. 2011;29:S29-38.
35. Benardot D. Timing of energy and fluid intake: New concepts for weight control and
hydration. ACSM's Health & Fitness Journal. 2007;11:13-19.
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36. Hawley J, Burke L. Effect of meal frequency and timing on physical performance, Br J
Nutr. 1997;77:S91-103.
Figure 1. Graphical depiction of how WDEB values were determined. Assessed values
include number of hours > 300 kcal; hours < 300 kcal; hours > 0 kcal; hours < 0 kcal
Modified from Benardot20. In contrast to the traditional method comparing energy intake with
total energy expenditure or exercise energy expenditure in 24-hour intervals, WDEB assesses
time and magnitude deviations from the predicted EB. Horizontal axis: energy status (kcal);
vertical axis: time course throughout the day (hours). The given example illustrates 5 hours with
WDEB > 0 kcal, 19 hours with WDEB < 0 kcal, 2 hours with WDEB > 300 kcal, and 7 hours
with WDEB < -300. Largest surplus is +426 kcal and largest deficit is -829 kcal. The 24-hour
energy balance is +19 kcal. Abbreviation: WDEB: within-day energy balance.
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Table 1. Description of subjects characterized by reproductive function
All Eumenorrhea MD P-value1
(n=25) (n=10) (n=15)
Age (years) 26.6 (5.6) 26.8 (4.6) 26.5 (6.3) 0.910
Height (cm) 169.9 (5.8) 170.0 (5.8) 168.1 (5.9) 0.081
Body weight (kg) 58.8 (7.3) 61.2 (8.2) 57.1 (6.4) 0.173
BMI (kg/m2) 20.6 (2.0) 21.2 (2.3) 20.2 (1.6) 0.228
Body fat (kg) 11.8 (3.1) 13.3 (3.1) 10.8 (2.8) 0.049
Body fat (%) 19.8 (3.6) 21.7 (3.3) 18.6 (3.3) 0.034
Fat free mass (kg) 46.0 (43.0 – 50.7) 49.2 (44.3 – 50.5) 46.0 (42.9 – 49.8) 0.482
Exercise (hours/week) 12.0 (4.4) 11.1 (2.9) 12.7 (5.1) 0.363
VO2peak (ml/kg/min) 54.5 (6.4) 53.0 (5.7) 55.5 (6.9) 0.354
Data are presented as mean (SD) for normally distributed data and as median and interquartile range (25-
75) for non-normally data. Abbreviations: BMI: body mass index, MD: menstrual dysfunction, VO2peak:
maximal oxygen uptake. 1) Difference between eumenorrheic and MD subjects.
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Table 2. Energy expenditure characterized by reproductive function
All Eumenorrhea MD P-value1
(n=25) (n=10) (n=15)
Total EE2 (kcal/day) 3247 (553) 3205 (443) 3276 (628) 0.761
DIT (kcal/day) 271 (44) 287 (54) 261 (34) 0.189
Exercise EE (kcal/day) 968 (571) 942 (295) 985 (568) 0.828
EPOC (kcal/day) 80 (38) 75 (24) 83 (46) 0.653
NEAT (kcal/day) 446 (147) 400 (74) 446 (177) 0.156
pRMR (kcal/hour) 64 (5) 65 (4) 63 (5) 0.498
pSMR (kcal/hour) 58 (5) 58 (4) 57 (5) 0.516
mRMR (kcal/hour) 57 (7) 60 (6) 55 (7) 0.063
RMRratio 0.89 (0.07) 0.93 (0.05) 0.87 (0.07) 0.033
Data are presented as mean (SD). Abbreviations: DIT: diet induced thermogenesis, EE: energy
expenditure, EPOC: excess post-exercise oxygen consumption, MD: menstrual dysfunction, mRMR:
measured resting metabolic rate, pRMR: predicted resting metabolic rate, pSMR: predicted sleeping
metabolic rate. 1) Difference between eumenorrheic and MD subjects. 2) Unadapted total energy
expenditure.
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Table 3. Within-day energy deficiency characterized by reproductive function
All Eumenorrhea MD P-value1
(n=25) (n=10) (n=15)
WDEB < 0 kcal
(hours/day) 22.1 (19.7 – 23.3) 21.1 (4.7 – 22.3) 23.0 (20.8 – 23.4) 0.048
WDEB <-300 kcal
(hours/day) 21.3 (15.7 – 22.3) 17.6 (3.9 – 20.9) 21.8 (17.8 – 22.4) 0.043
Largest hourly deficit
(kcal) -2626 (2352) -1793 (2360) -3181 (2253) 0.159
Data are presented as mean (SD) for normally distributed data and as median and interquartile range (25-
75) for non-normally distributed data. Abbreviations: MD: menstrual dysfunction, WDEB: within-day
energy balance. 1) Difference between eumenorrheic and MD subjects.
Table 4. Associations between within-day energy deficiency and markers for catabolic state
Hours with WDEB < 0 kcal Hours with WDEB <-300 kcal Largest hourly deficit1
r P-value r P-value r P-value
RMRratio -0.487 0.013 -0.472 0.018 0.310 0.132
Body fat (%) -0.313 0.128 -0.337 0.100 0.023 0.913
Cortisol 0.442 0.027 0.463 0.019 -0.297 0.111
Estradiol -0.433 0.034 -0.516 0.009 0.505 0.012
T3 -0.360 0.078 -0.264 0.203 0.287 0.164
Glucose -0.350 0.086 -0.365 0.073 0.202 0.333
All subjects (n=25) were included in the correlation analysis. Abbreviations: RMR: resting metabolic rate,
WDEB: within-day energy balance. 1)values recorded as negative numbers.
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