Effect of exercise training on metabolic ﬂexibility in response to a high-fat
diet in obese individuals
Gina M. Battaglia,
Robert C. Hickner,
and Joseph A. Houmard
Department of Kinesiology, College of Health and Human Performance, East Carolina University, Greenville, North
Human Performance Laboratory, College of Health and Human Performance, East Carolina University,
Greenville, North Carolina; and
East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville,
Submitted 12 July 2012; accepted in ﬁnal form 7 October 2012
Battaglia GM, Zheng D, Hickner RC, Houmard JA. Effect of exercise
training on metabolic ﬂexibility in response to a high-fat diet in obese
individuals. Am J Physiol Endocrinol Metab 303: E1440 –E1445, 2012. First
published October 9, 2012; doi:10.1152/ajpendo.00355.2012.—Obese indi-
viduals typically exhibit a reduced capacity for metabolic ﬂexibility
by failing to increase fatty acid oxidation (FAO) upon the imposition
of a high-fat diet (HFD). Exercise training increases FAO in the
skeletal muscle of obese individuals, but whether this intervention can
restore metabolic ﬂexibility is unclear. The purpose of this study was
to compare FAO in the skeletal muscle of lean and obese subjects in
response to a HFD before and after exercise training. Twelve lean
(means ⫾SE) (age 21.8 ⫾1.1 yr, BMI 22.6 ⫾0.7 kg/m
) and 10
obese men (age 22.4 ⫾0.8 yr, BMI 33.7 ⫾0.7 kg/m
) consumed a
eucaloric HFD (70% of energy from fat) for 3 days. After a washout
period, 10 consecutive days of aerobic exercise (1 h/day, 70%
) were performed, with the HFD repeated during days 8 –10.
FAO and indices of mitochondrial content were determined from
muscle biopsies. In response to the HFD, lean subjects increased
complete FAO (27.3 ⫾7.4%, P⫽0.03) in contrast to no change in
their obese counterparts (1.0 ⫾7.9%). After 7 days of exercise, citrate
synthase activity and FAO increased (P⬍0.05) regardless of body
habitus; addition of the HFD elicited no further increase in FAO.
These data indicate that obese, in contrast to lean, individuals do not
increase FAO in skeletal muscle in response to a HFD. The increase
in FAO with exercise training, however, enables the skeletal muscle
of obese individuals to respond similarly to their lean counterparts
when confronted with short-term excursion in dietary lipid.
skeletal muscle; fat oxidation; mitochondria; physical activity
THE PREVALENCE OF OBESITY has been increasing rapidly and is
strongly associated with the development of insulin resistance,
the metabolic syndrome, and type 2 diabetes (10). An impor-
tant indicator of metabolic health is metabolic ﬂexibility,
which is the ability to adjust substrate utilization to changes in
substrate availability (16). For example, in lean individuals,
fatty acid oxidation (FAO) at the whole body level increases
with the imposition of a high-fat diet (HFD); to the contrary,
obese individuals display an impaired capacity to increase
FAO in the face of an elevation in dietary lipid (1, 11, 15, 21).
In the skeletal muscle of lean individuals, a HFD also increased
the transcription of genes involved in fatty acid transport and
oxidation in contrast to minimal or no changes in their obese
counterparts (3, 6, 20). This inability to increase FAO when
lipid presence is elevated creates a condition of positive fat
balance, which in skeletal muscle may lead to ectopic lipid
accumulation (21), lipid peroxidation (23), and excessive in-
creases in lipid intermediates such as diacylglycerol and cer-
amide, resulting in intracellular lipotoxicity (18).
Our research has demonstrated that obese and formerly
severely obese (BMI ⬎40 kg/m
) individuals who lost weight
increased lipid oxidation in skeletal muscle to the same extent
as lean subjects with 10 days of endurance-oriented exercise
training (2). However, it is not evident whether exercise train-
ing restores metabolic ﬂexibility with respect to adjusting
appropriately (i.e., similar to lean subjects) to an increase in
dietary lipid. The purposes of the present study were to deter-
mine 1) whether the skeletal muscle of young, obese individ-
uals lacks metabolic ﬂexibility in terms of increasing FAO in
response to a HFD and 2) whether exercise training can correct
any impairment in metabolic ﬂexibility evident with obesity.
Subjects. Twelve lean (BMI ⱕ25 kg/m
) and 10 obese (BMI
) male subjects aged 18 –30 yr volunteered to participate.
Subjects were not involved in an aerobic training program, as deter-
mined by a physical activity questionnaire and verbal questioning, and
were asked to not change their physical activity patterns throughout
the duration of the study. Participants ﬁlled out a medical history to
conﬁrm that they were free from disease, did not smoke, and were not
taking any medications known to inﬂuence carbohydrate or lipid
metabolism. Subjects were weight stable (⫾2 kg over the past 3 mo)
and nonsmokers. The experimental procedure and associated risks
were explained in written and oral format, and informed consent was
obtained. The study was approved by the East Carolina Policy and
Review Committee on Human Research and was in accordance with
the Declaration of Helsinki.
Study design. Each participant consumed a eucaloric HFD for 3
days while sedentary. After a 2- to 3-wk washout period, subjects
exercised for 10 consecutive days and consumed a eucaloric HFD
from days 8 to 10 of exercise training (Fig. 1). A 2-wk washout has
been used in other studies examining the effects of a HFD and
exercise (5, 27). Skeletal muscle biopsies were obtained from the
vastus lateralis after a 12-h overnight fast on the morning that the
HFD was initiated and on the morning after the 3 days of the HFD.
Blood samples were taken at the initial screening and biopsy visits.
Diet. The HFD consisted of ⬃70% fat, 15% carbohydrate, and 15%
protein and was calculated to be eucaloric and maintain body mass. In
our preliminary studies, this fat proportion and duration (3 days)
increased FAO in skeletal muscle by 38% in four lean subjects (data
not shown), and another group reported that a similar diet increased
pyruvate dehydrogenase kinase 4 (PDK4) content and activity in
skeletal muscle (20). Energy content for each individual was deter-
mined from the Harris-Benedict equation (13), and mean macronutri-
ent content (per kg body mass) was 2.5 g/kg fat, 1.2 g/kg carbohy-
drate, and 1.0 g/kg protein; 21% of the energy intake from fat
consisted of saturated fats. Subjects were weighed before and after the
Address for correspondence: J. A. Houmard, Human Performance Labora-
tory, Ward Sports Medicine Bldg., East Carolina University, Greenville, NC
27858 (e-mail: email@example.com).
Am J Physiol Endocrinol Metab 303: E1440–E1445, 2012.
First published October 9, 2012; doi:10.1152/ajpendo.00355.2012.
0193-1849/12 Copyright ©2012 the American Physiological Society http://www.ajpendo.orgE1440
HFD and at the beginning of exercise training to ensure that body
weight did not change throughout the duration of the study. The 3-day
diet regimen was described to each subject in detail, emphasizing the
importance of consuming only the items indicated. Some meals were
from fast-food chains, and subjects ordered the exact items and
returned dated receipts to ensure compliance. The remainder of the
food items were prepackaged and labeled in the appropriate amount
for each given day and provided to the participants. Subjects logged
their intake. On the day prior to commencement of the HFD, subjects
were provided an isocaloric diet consisting of ⬃25% fat, 15% protein,
and 60% carbohydrates. All diets and food logs were analyzed by
Nutritionist Pro Nutrition Analyst Software (Axxya Systems, Staf-
ford, TX) to ensure correct macronutrient composition.
Exercise training. An incremental maximal exercise test on an
electronically braked cycle ergometer was performed to determine
peak oxygen uptake (V
) during the screening process. Partici-
pants then exercised 60 min/day at 70% V
for 10 consecutive
days. All training was supervised and performed in the laboratory
setting; heart rate was monitored throughout each training session and
measurements were taken periodically to ensure proper work-
load. Net energy utilized during exercise training was determined
using indirect calorimetry and the resulting energy added to the diets
during days 8 –10 of exercise. Exercise was performed 14 –18 h before
the muscle biopsies on days 7 and 10.
Muscle analyses. Fatty acid oxidation was measured as described
previously (2, 14, 17). Brieﬂy, 50 – 60 mg of muscle tissue was
collected in 200 l of a buffer containing 250 mM sucrose, 1 mM
EDTA, and 10 mM Tris·HCl, pH 7.4. Samples were minced with
scissors to remove excess fat and connective tissue and diluted 20-fold
with additional buffer. Tissue was placed on ice and homogenized
with a Teﬂon pestle for 30 s. Forty microliters of homogenate was
added to the top well of a sealed, modiﬁed 48-well plate that contained
a channel connecting to the adjacent trap well, which allowed for the
passage of CO
liberated by the complete oxidation of [1-
tate. The bottom trap well contained 1 N sodium hydroxide to collect
given off by the oxidation procedure. To initiate the
reaction, 160 l of a reaction buffer composed of the following was
added to the top wells: 0.2 mM palmitate ([1-
C]palmitate at 0.5
Ci/ml), 100 mM sucrose, 10 mM Tris·HCl, 5 mM potassium phos-
phate, 80 mM potassium chloride, 1 mM magnesium chloride, 0.1
mM malate, 2 mM ATP, 1 mM dithiothreitol, 0.2 mM EDTA, 1 mM
L-carnitine, 0.5 mM coenzyme A, and 0.5% fatty acid-free bovine
serum albumin, pH 7.4. The samples were incubated in a 37°C water
bath for 30 min, at which point 100 l of 70% perchloric acid was
added to terminate the reaction. The plate was placed on a shaker for
1 h to ensure complete transfer of CO
into the bottom well. Label
was determined by scintillation counting
using 4 ml of Uniscient BD (National Diagnostics, Atlanta, GA).
Incomplete oxidative products (acid-soluble metabolites) remaining in
the top well were measured as described previously (17).
A 10- to 15-mg piece of muscle was homogenized at 4°C using a
Bullet Blender (Next Advance, Averill Park, NY) in a lysis buffer
containing 50 mM HEPES, 12 mM sodium pyrophosphate, 100 mM
sodium ﬂuoride, 10 mM EDTA, 1% Triton X-100, and 0.1% SDS and
supplemented with protease and phosphatase inhibitors (Sigma-Al-
drich). Samples were rotated end over end on a rotating wheel for 1
h at 4°C and centrifuged at 21,000 gfor 20 min at 10°C. Protein
concentrations were determined using the bicinchoninic acid assay
(Pierce Biotechnology, Rockford, IL). Five micrograms of protein
was separated by SDS-PAGE and electrotransfered to polyvi-
nylidened ﬂouride membranes (Millipore, Billerica, MA) and probed
overnight for cytochrome coxidase IV (1:1,000; Cell Signaling
Technology, Beverly, MA) and with a cocktail containing antibodies
against the following proteins (1:1,000): complex I subunit NDUFB8,
complex II subunit 30 kDa, complex III subunit core 2, complex IV
subunit II, and ATP synthase subunit-␣(Mitosciences, Eugene, OR).
Membranes were incubated for1hatroom temperature with the
corresponding secondary antibody, and the immunoreactive proteins
were detected using enhanced chemiluminescence (ChemiDoc XRS⫹
Imaging System; Bio-Rad Laboratories, Hercules, CA). Samples were
normalized to a crude muscle homogenate sample on each gel to
normalize for blotting efﬁciency across gels.
A 10- to 15-mg piece of muscle was diluted 20-fold in a buffer
containing 100 mM KH
and 0.05% bovine serum albumin and
homogenized at 4°C using the Bullet Blender. Homogenates went
through four freeze-thaw cycles before experimentation. This homog-
enate was used for determining citrate synthase (CS) and ␤-hydroxy-
acetyl coenzyme A dehydrogenase (HAD) activity. Protein content
was measured using the bicinchoninic acid assay. CS activity was
assessed with reagents provided in a kit (Sigma CS0720), which used
a colorimetric reaction to measure the reaction rate of acetyl coen-
zyme A and oxaloacetic acid. Activity of HAD was measured using
methods described previously (26), and rates were determined by
calculating the rate of disappearance of NADH after the addition of
acetoacetyl coenzyme A.
Statistical analyses. Two-way repeated-measures analysis of vari-
ance was used to compare the data. Post hoc analyses were performed
using contrast-contrast analysis. Statistical signiﬁcance was set at Pⱕ
0.05, and all data are expressed as means ⫾SE. Because of limitations
in tissue size, all measurements could not be obtained for all individ-
uals; the nfor each variable is indicated.
Anthropometric data are presented in Table 1. Body mass,
BMI, fasting insulin, and homeostatic model assessment of
insulin resistance were signiﬁcantly higher in the obese sub-
Table 1. Subject characteristics
Lean (n⫽12) Obese (n⫽10)
Age, yr 21.8 ⫾1.1 22.4 ⫾0.8
Height, cm 178.9 ⫾2.0 179.1 ⫾2.2
Mass, kg 72.2 ⫾2.4 108.4 ⫾3.3*
22.6 ⫾0.7 33.7 ⫾0.7*
Body fat, % 17.7 ⫾1.8 37.5 ⫾1.8*
Fasting glucose, mmol/l 4.7 ⫾0.1 4.7 ⫾0.1
Fasting insulin, mol/l 44 ⫾878⫾8*
HOMA-IR 1.3 ⫾0.2 2.4 ⫾0.3*
Plasma cholesterol, mmol/l 3.97 ⫾0.21 4.62 ⫾0.31
Plasma triglycerides, mmol/l 0.82 ⫾0.10 1.37 ⫾0.19*
36.7 ⫾1.2 27.2 ⫾1.2*
, l/min 2.6 ⫾0.2 2.9 ⫾0.2
Results are expressed as means ⫾SE. HOMA-IR, homeostatic model
assessment of insulin resistance. *Signiﬁcantly different (P⬍0.05) from lean.
Fig. 1. Study design. Subjects were screened and tested for maximal aerobic
) before commencement of the study. Within 4 wk of
screening, subjects underwent a fasting muscle biopsy of the vastus lateralis,
consumed an isocaloric 70% high-fat diet (HFD) for 3 days (3d), and then had
another muscle biopsy on the morning after the ﬁnal day of the HFD. After a
2- to 3-wk washout period, subjects began exercise training for 10 consecu-
tive days (10d), 1 h/day, at 70% peak oxygen consumption. On the morning of
day 8, subjects had a muscle biopsy and began consuming the HFD during
days 8–10 of exercise training. The day after the exercise training and second
HFD was ﬁnished, subjects underwent their ﬁnal muscle biopsy.
E1441EXERCISE, METABOLIC FLEXIBILITY, AND OBESITY
AJP-Endocrinol Metab •doi:10.1152/ajpendo.00355.2012 •www.ajpendo.org
jects (P⬍0.01). Blood lipids, glucose, and insulin did not
change as a result of the HFD or exercise training and were not
associated with FAO or mitochondrial content (data not shown).
All subjects remained weight stable throughout the course of the
study, and there were no changes in body mass in either group
(data not shown). The diet composition was similar between lean
and obese subjects (72% fat, 15% carbohydrate, and 13% protein)
and provided a signiﬁcant increase in dietary fat over their normal
consumption determined from 3-day food logs performed before
commencement of the study (35% fat, 48% carbohydrate, and
Fatty acid oxidation in skeletal muscle. Fatty acid oxidation
in response to the high-fat diet and exercise training are
presented in Fig. 2. The lean subjects increased complete
palmitate oxidation (
production) by 27% in response to
the 3-day HFD (P⫽0.03), indicating metabolic ﬂexibility in
response to an increase in dietary lipid. However, there was
essentially no alteration in FAO in the obese group (1%
increase vs. prediet values; Fig. 2), indicating a lack of meta-
bolic ﬂexibility. Exercise training (P⫽0.02) and 10 days of
exercise plus the 3-day HFD (P⫽0.002) increased FAO above
preexercise levels in both groups; however, in relation to meta-
bolic ﬂexibility, there was no signiﬁcant increase in FAO with the
addition of the HFD after the 7 days of exercise (Fig. 2). Total
FAO (overall average 1,450.8 nmol·mg protein
acid-soluble metabolites (overall average 1,157.3 nmol·mg
) did not change with the HFD or exercise train-
ing and were not different between the lean and obese groups
(data not shown).
Skeletal muscle enzyme activities/protein content. Enzyme
activities for CS and HAD are presented in Fig. 3, Aand B,
respectively. In the sedentary state, CS activity exhibited a
pattern similar to complete FAO (Fig. 2), with a tendency for
the lean subjects to increase (12.3 ⫾7.3%, P⫽0.17) in
response to the HFD and the obese subjects to have an
attenuated response (⫺2.3 ⫾8.9% decrease from prediet
values). Seven days of exercise training increased CS activity
in both groups over the sedentary condition (P⫽0.02), with no
further change at 10 days of exercise plus the HFD (P⫽0.03
compared with sedentary prediet) (Fig. 3A). The trends for
HAD responses to the HFD and exercise training were similar
to CS, with a HFD plus exercise increase that approached
statistical signiﬁcance (P⫽0.07 compared with sedentary
prediet; Fig. 3B). Protein content of complexe II, III, and IV
and ATP synthase subunits did not change with the HFD or
exercise training and were not different between lean and obese
individuals (Fig. 4).
A decrement in metabolic ﬂexibility with obesity was ﬁrst
observed by Kelley et al. (15), who reported an inability to
increase carbohydrate oxidation in response to euglycemic/
hyperinsulinemic conditions. In terms of lipid availability, both
whole body fat oxidation (1) and the transcription of genes
Fig. 3. Citrate synthase (CS; A) and hydroxy coenzyme A dehydrogenase
(HAD; B) prediet, after 3d HFD, after 7d exercise, and after 10d exercise ⫹3d
HFD. CS activity was determined from 12 lean and 9 obese subjects, whereas
HAD was determined from 10 lean and 8 obese subjects. Results are expressed
as means ⫾SE. ‡Signiﬁcant treatment effect for 7d exercise compared with
the prediet condition (P⫽0.02); §signiﬁcant treatment effect for the 10d
exercise ⫹HFD compared with the prediet condition (P⫽0.03).
Fig. 2. Complete palmitate oxidation (
production from palmitate) in
skeletal muscle biopsies prediet, following a 3d HFD in the sedentary condi-
tion, after 7 days of exercise, and after a 3d HFD ⫹10d exercise in lean (n⫽
9) and obese (n⫽8) men. Results are expressed as means ⫾SE. *Signiﬁcantly
different from obese after the 3d HFD (P⫽0.02); †signiﬁcantly increased
compared with the prediet condition for lean (P⫽0.02); ‡signiﬁcant treatment
effect for 7 days (7d) of exercise compared with the prediet condition (P⫽
0.02); §signiﬁcant treatment effect for the 10d exercise ⫹HFD compared with
the prediet condition (P⬍0.01).
E1442 EXERCISE, METABOLIC FLEXIBILITY, AND OBESITY
AJP-Endocrinol Metab •doi:10.1152/ajpendo.00355.2012 •www.ajpendo.org
regulating fat oxidation in skeletal muscle (3) increased in lean
individuals, whereas their obese counterparts exhibited damp-
ened responses with the imposition of a HFD. The ability to
adjust FAO appropriately in response to excursions in dietary
lipid is a critical component of metabolic health because
inﬂexibility may lead to positive fat balance (11), ectopic lipid
accumulation (29), and weight gain (21). In terms of interven-
tion, FAO in skeletal muscle increases in both lean and obese
individuals with relatively short-term (10-day) endurance-ori-
ented exercise training (2); however, it is not evident whether
exercise training can rescue (i.e., induce a response similar to
that seen in lean subjects) the impairment in metabolic ﬂexi-
bility evident with obesity. The main ﬁndings of the present
study were that 1) relatively young, obese individuals lack
metabolic ﬂexibility in terms of increasing FAO in skeletal
muscle in response to a HFD and 2) exercise training increases
FAO in skeletal muscle, which enables obese individuals to
respond to an increase in dietary lipid in a manner similar to
In the current study the lean, but not obese, group increased
complete FAO in skeletal muscle in response to the 3-day HFD
(Fig. 2), which corresponds with other studies at the whole
body level (1, 29). We have reported previously that obese
individuals exhibited a diminished capacity to increase the
expression of genes that regulate fatty acid transport and
utilization in response to a HFD (3). The current ﬁndings
provide the additional information that this impairment in gene
expression with obesity likely contributes, at least in part, to
the inability to upregulate FAO in the face of increased lipid
availability (Fig. 2). However, although the patterns of change
in CS, which can reﬂect mitochondrial content (30), and FAO
were similar in the lean subjects (Figs. 2 and 3), it is likely that
factors involved with enhanced mitochondrial function also
contributed to the increases in FAO. PDK4, an enzyme that
inhibits activity of the pyruvate dehydrogenase complex, re-
sponds rapidly to increases in lipid presence that would in turn
partition substrates toward FAO (8). A HFD increased PDK4
protein content and overall PDK activity in lean individuals
signiﬁcantly after only 1 day (20), and PDK4 mRNA was
increased in lean but not obese individuals after a 5-day 60%
fat diet (3). Thus, an inability to increase PDK4 content with
obesity may help explain the differential response to the HFD
(Fig. 2); however, this is conjecture, because limitations in
tissue size prevented us from determining PDK4 content. Also,
one of the limitations of this study was that sufﬁcient tissue
could not be obtained for all analyses, which may have com-
promised the power for detecting statistical differences in
measurements such as CS activity.
A novel feature of the current study was the inclusion of
short-term aerobic exercise training as a possible means for
Fig. 4. Protein content of mitochondrial elec-
tron transport chain enzyme subunits prediet,
after 3d HFD, after 7d exercise, and after 10d
exercise ⫹3d HFD in 9 lean and 8 obese
subjects. A: ATP synthase subunit-␣.B: com-
plex III core 2. C: cytochrome coxidase IV
(COX IV). D: complex II 30 kDa. Results are
expressed as means ⫾SE.
E1443EXERCISE, METABOLIC FLEXIBILITY, AND OBESITY
AJP-Endocrinol Metab •doi:10.1152/ajpendo.00355.2012 •www.ajpendo.org
improving metabolic ﬂexibility. The 7 days of exercise training
increased skeletal muscle FAO to the same extent in both
groups of subjects (Fig. 2), indicative of no resistance to the
intervention with obesity. Similar increases in FAO were
reported in lean, obese, and post-gastric bypass subjects (2) and
in lean and obese Caucasian and African-American women (9)
with 10 days of exercise, suggesting that FAO in skeletal
muscle increases rapidly regardless of body habitus. However,
to our knowledge, no studies have directly examined the effect
of exercise training on metabolic ﬂexibility in relation to an
increase in dietary lipid. We observed that with the addition of
the HFD neither the lean nor obese groups signiﬁcantly in-
creased FAO above that which was evident after exercise
training alone (Fig. 2); this lack of a response indicates tech-
nically that metabolic ﬂexibility, i.e., the ability to increase
FAO with respect to increased lipid availability, was not
enhanced. However, it is important to note that exercise train-
ing increased FAO equivalent to or beyond the increment seen
in response to the HFD alone (Fig. 2). These ﬁndings suggest
that a high absolute capacity for FAO can render the skeletal
muscle of the obese effective in dealing with increased dietary
lipid and minimizing positive lipid balance, although an en-
hanced ability to adjust utilization (metabolic ﬂexibility) per se
is not evident.
With exercise training, CS and HAD activities mirrored the
pattern of FAO changes, with CS activity elevated compared
with the sedentary condition at both 7 and 10 days (Fig. 3).
Endurance-oriented exercise training has been shown to be a
potent means for rapidly (7–14 days) improving the maximal
activity and content of mitochondrial proteins (4, 25, 28) in
lean individuals. Although previous research in rodents have
shown an additive effect of exercise training and a HFD on CS
and HAD activities (7, 24), these enzymes did not change
either with the addition of a HFD in endurance-trained humans
(12) or in the present study (Fig. 3), implying either a species
difference or that the increase in mitochondrial content with
exercise training in humans is sufﬁcient to adjust to subsequent
increases in dietary lipid. Similarly, rats bred for high intrinsic
running capacity had higher skeletal muscle lipid oxidation
rates compared with their low intrinsic running capacity coun-
terparts, which was due primarily to increased oxidative ca-
pacity and mitochondrial content in the white muscle ﬁbers
(22). However, the current data cannot dismiss the possibility
that improvements in mitochondrial function also contributed
to the enhanced capacity for FAO.
Electron transport chain content was not altered with the HFD
or exercise training and did not differ with obesity (Fig. 4). The
temporal pattern of gene expression likely varies, because
Perry et al. (19) showed that CS and HAD activities increased
after 6 days of training, whereas cytochrome coxidase subunit
IV content did not increase until 10 days. However, the training
protocol of our study was moderate (1 h at 70% V
compared with the one employed by Perry et al. (19). There-
fore, the higher intensity of the former may have elicited a
more robust response in mitochondrial content compared with
In conclusion, 3 days of a HFD increased lipid oxidation in
the skeletal muscle of lean but not obese individuals, which
was indicative of an impairment in metabolic ﬂexibility with
obesity. Endurance-oriented exercise training increased lipid
oxidation and CS activity in skeletal muscle regardless of body
habitus, with no incremental improvement with the addition of
a HFD. These ﬁndings suggest that the increase in FAO in
skeletal muscle with endurance-oriented exercise training en-
ables obese individuals to respond similarly to their lean
counterparts when confronted with an increase in dietary lipid
We thank Angela Clark and Rita Bowden for assisting with specimen
collection and the undergraduate student assistants at East Carolina University
for assisting with exercise training and testing.
Funding for this work was provided by a grant from the National Institute
of Diabetes and Digestive and Kidney Diseases (DK-056112, J. A. Houmard).
The authors have no conﬂicts of interest, ﬁnancial or otherwise, to declare.
G.M.B. and J.A.H. did the conception and design of the research; G.M.B.,
D.Z., R.C.H., and J.A.H. performed the experiments; G.M.B. and D.Z. ana-
lyzed the data; G.M.B., D.Z., and J.A.H. interpreted the results of the
experiments; G.M.B. and J.A.H. prepared the ﬁgures; G.M.B. and J.A.H.
drafted the manuscript; G.M.B. and J.A.H. edited and revised the manuscript;
G.M.B. and J.A.H. approved the ﬁnal version of the manuscript.
1. Astrup A, Buemann B, Christensen NJ, Toubro S. Failure to increase
lipid oxidation in response to increasing dietary fat content in formerly
obese women. Am J Physiol Endocrinol Metab 266: E592–E599, 1994.
2. Berggren JR, Boyle KE, Chapman WH, Houmard JA. Skeletal muscle
lipid oxidation and obesity: inﬂuence of weight loss and exercise. Am J
Physiol Endocrinol Metab 294: E726 –E732, 2008.
3. Boyle KE, Canham JP, Consitt LA, Zheng D, Koves TR, Gavin TP,
Holbert D, Neufer PD, Ilkayeva O, Muoio DM, Houmard JA. A
high-fat diet elicits differential responses in genes coordinating oxidative
metabolism in skeletal muscle of lean and obese individuals. J Clin
Endocrinol Metab 96: 775–781, 2011.
4. Burgomaster KA, Cermak NM, Phillips SM, Benton CR, Bonen A,
Gibala MJ. Divergent response of metabolite transport proteins in human
skeletal muscle after sprint interval training and detraining. Am J Physiol
Regul Integr Comp Physiol 292: R1970 –R1976, 2007.
5. Burke LM, Angus DJ, Cox GR, Cummings NK, Febbraio MA,
Gawthorn K, Hawley JA, Minehan M, Martin DT, Hargreaves M.
Effect of fat adaptation and carbohydrate restoration on metabolism and
performance during prolonged cycling. J Appl Physiol 89: 2413–2421,
6. Cameron-Smith D, Burke LM, Angus DJ, Tunstall RJ, Cox GR,
Bonen A, Hawley JA, Hargreaves M. A short-term, high-fat diet up-
regulates lipid metabolism and gene expression in human skeletal muscle.
Am J Clin Nutr 77: 313–318, 2003.
7. Cheng B, Karamizrak O, Noakes TD, Dennis SC, Lambert EV. Time
course of the effects of a high-fat diet and voluntary exercise on muscle
enzyme activity in Long-Evans rats. Physiol Behav 61: 701–705, 1997.
8. Chokkalingam K, Jewell K, Norton L, Littlewood J, van Loon LJ,
Mansell P, Macdonald IA, Tsintzas K. High-fat/low-carbohydrate diet
reduces insulin-stimulated carbohydrate oxidation but stimulates nonoxi-
dative glucose disposal in humans: An important role for skeletal muscle
pyruvate dehydrogenase kinase 4. J Clin Endocrinol Metab 92: 284–292,
9. Cortright RN, Sandhoff KM, Basilio JL, Berggren JR, Hickner RC,
Hulver MW, Dohm GL, Houmard JA. Skeletal muscle fat oxidation is
increased in African-American and white women after 10 days of endur-
ance exercise training. Obesity (Silver Spring) 14: 1201–1210, 2006.
10. Flegal KM, Carroll MD, Ogden CL, Johnson CL. Prevalence and
trends in obesity among US adults, 1999 –2000. JAMA 288: 1723–1727,
11. Galgani JE, Moro C, Ravussin E. Metabolic ﬂexibility and insulin
resistance. Am J Physiol Endocrinol Metab 295: E1009 –E1017, 2008.
E1444 EXERCISE, METABOLIC FLEXIBILITY, AND OBESITY
AJP-Endocrinol Metab •doi:10.1152/ajpendo.00355.2012 •www.ajpendo.org
12. Goedecke JH, Christie C, Wilson G, Dennis SC, Noakes TD, Hopkins
WG, Lambert EV. Metabolic adaptations to a high-fat diet in endurance
cyclists. Metabolism 48: 1509 –1517, 1999.
13. Harris JA, Benedict FG. A Biometric Study of Human Basal Metabo-
lism. Proc Natl Acad Sci USA 4: 370 –373, 1918.
14. Jong-Yeon K, Hickner RC, Dohm GL, Houmard JA. Long- and
medium-chain fatty acid oxidation is increased in exercise-trained human
skeletal muscle. Metabolism 51: 460 –464, 2002.
15. Kelley DE, Goodpaster B, Wing RR, Simoneau JA. Skeletal muscle
fatty acid metabolism in association with insulin resistance, obesity, and
weight loss. Am J Physiol Endocrinol Metab 277: E1130 –E1141, 1999.
16. Kelley DE, Mandarino LJ. Fuel selection in human skeletal muscle in
insulin resistance: a reexamination. Diabetes 49: 677–683, 2000.
17. Kim JY, Hickner RC, Cortright RL, Dohm GL, Houmard JA. Lipid
oxidation is reduced in obese human skeletal muscle. Am J Physiol
Endocrinol Metab 279: E1039 –E1044, 2000.
18. Moro C, Galgani JE, Luu L, Pasarica M, Mairal A, Bajpeyi S,
Schmitz G, Langin D, Liebisch G, Smith SR. Inﬂuence of gender,
obesity, and muscle lipase activity on intramyocellular lipids in sedentary
individuals. J Clin Endocrinol Metab 94: 3440 –3447, 2009.
19. Perry CG, Lally J, Holloway GP, Heigenhauser GJ, Bonen A, Spriet
LL. Repeated transient mRNA bursts precede increases in transcriptional
and mitochondrial proteins during training in human skeletal muscle. J
Physiol 588: 4795–4810, 2010.
20. Peters SJ, Harris RA, Wu P, Pehleman TL, Heigenhauser GJ, Spriet
LL. Human skeletal muscle PDH kinase activity and isoform expression
during a 3-day high-fat/low-carbohydrate diet. Am J Physiol Endocrinol
Metab 281: E1151–E1158, 2001.
21. Ravussin E. Metabolic differences and the development of obesity.
Metabolism 44: 12–14, 1995.
22. Rivas DA, Lessard SJ, Saito M, Friedhuber AM, Koch LG, Britton
SL, Yaspelkis BB 3rd, Hawley JA. Low intrinsic running capacity is
associated with reduced skeletal muscle substrate oxidation and lower
mitochondrial content in white skeletal muscle. Am J Physiol Regul Integr
Comp Physiol 300: R835–R843, 2011.
23. Russell AP, Gastaldi G, Bobbioni-Harsch E, Arboit P, Gobelet C,
Deriaz O, Golay A, Witztum JL, Giacobino JP. Lipid peroxidation in
skeletal muscle of obese as compared to endurance-trained humans: a case
of good vs. bad lipids? FEBS Lett 551: 104 –106, 2003.
24. Simi B, Sempore B, Mayet MH, Favier RJ. Additive effects of training
and high-fat diet on energy metabolism during exercise. J Appl Physiol 71:
25. Spina RJ, Chi MM, Hopkins MG, Nemeth PM, Lowry OH, Holloszy
JO. Mitochondrial enzymes increase in muscle in response to 7–10 days
of cycle exercise. J Appl Physiol 80: 2250 –2254, 1996.
26. Srere PA. Citrate synthase. In: Methods in Enzymology, edited by Low-
enstein JM. New York: Academic, 1969, p. 3–11.
27. Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M,
Hawley JA, Burke LM. Decreased PDH activation and glycogenolysis
during exercise following fat adaptation with carbohydrate restoration. Am
J Physiol Endocrinol Metab 290: E380 –E388, 2006.
28. Talanian JL, Galloway SD, Heigenhauser GJ, Bonen A, Spriet LL.
Two weeks of high-intensity aerobic interval training increases the capac-
ity for fat oxidation during exercise in women. J Appl Physiol 102:
1439 –1447, 2007.
29. Thomas CD, Peters JC, Reed GW, Abumrad NN, Sun M, Hill JO.
Nutrient balance and energy expenditure during ad libitum feeding of
high-fat and high-carbohydrate diets in humans. Am J Clin Nutr 55:
934 –942, 1992.
30. Tunstall RJ, Mehan KA, Wadley GD, Collier GR, Bonen A, Har-
greaves M, Cameron-Smith D. Exercise training increases lipid metab-
olism gene expression in human skeletal muscle. Am J Physiol Endocrinol
Metab 283: E66 –E72, 2002.
E1445EXERCISE, METABOLIC FLEXIBILITY, AND OBESITY
AJP-Endocrinol Metab •doi:10.1152/ajpendo.00355.2012 •www.ajpendo.org