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MINIREVIEW
Leptin and Exercise
ROBERT R. KRAEMER,
1,
*HONGNAN CHU,* AND V. DANIEL CASTRACANE†
*Department of Kinesiology and Health Studies, Southeastern Louisiana University, Hammond,
Louisiana 70402; and †Department of Obstetrics and Gynecology and Women’s Health Research
Institute of Amarillo, Texas Tech University Health Sciences Center, Amarillo, Texas 79106
Short-term exercise (<60 min) studies suggest that leptin con-
centrations are not acutely affected in healthy males and fe-
males. Most reports of reductions in serum leptin may be at-
tributed to circadian rhythms or hemoconcentration. For long-
term (≥ 60 min) exercise, a reduction in leptin concentrations
reported from 1 to 3 hr of running or cycling has been attributed
to diurnal reduction in circulating leptin, independent of exer-
cise. Exercise that produces a sufficient energy imbalance
(kilocalorie intake versus kilocalorie expenditure) suppresses
24-hr mean and amplitude of the diurnal rhythm of leptin in
women. Suppression of leptin concentrations may be counter-
balanced by feeding and may explain consistent reports of
reductions in leptin concentrations following extreme bouts
of exercise such as marathons or ultramarathons. In addition,
leptin concentrations are reduced 48 hr after long-term aerobic
exercise and long-term resistance exercise is associated with
delayed leptin reduction 9 hr postexercise. Training studies
have documented that short-term exercise training (≤ 12 weeks)
does not affect leptin levels, with the exception of patients with
type 2 diabetes. Exercise training protocols that result in re-
duced fat mass will lower leptin concentrations, thus, most in-
vestigators have reported leptin concentrations after account-
ing for fat loss. There are disparate findings concerning long-
term (>12 weeks) training studies, with a number of studies
finding no effect of training on leptin concentrations other than
effects induced by fat loss, and other studies finding reductions
in leptin concentrations after accounting for fat loss. Exercise
training-induced reductions in leptin levels have been attrib-
uted to alterations in energy balance, improvements in insulin
sensitivity, alterations in lipid metabolism, and unknown fac-
tors. Hormone replacement does not seem to affect leptin ad-
aptations to training. Patients with type 2 diabetes show de-
layed effects of short-term resistance exercise on leptin con-
centrations, reduced leptin levels with long-term training, and
appear to be more sensitive to training-induced leptin adapta-
tions than other populations.
Exp Biol Med 227:701–708, 2002
Key words: exercise; leptin; endocrinology; human.
L
eptin was discovered in 1994 following the isolation
of the ob gene (1). Leptin, a protein with a helical
structure similar to cytokines and a relative mass of
16 kDa (2), assists in the regulation of body weight and
energy homeostasis (3, 4). Adipose tissue is the major
source of leptin expression, however, other sites have been
identified, including skeletal muscle, mammary epithelium,
the placenta, and the brain (2). It is thought that a major role
of leptin is to relay information to signal transducing recep-
tors in the hypothalamus concerning the status of energy
stores (5, 6) and thus aid in reduced feeding (3, 4). The
discovery of leptin has led to numerous experiments to bet-
ter understand its function, and a portion of those studies
have focused on leptin and exercise. In this minireview, we
will summarize the role of leptin in energy balance and
reproduction and we then discuss the existing prospective
research concerning the effects of exercise on leptin in
humans.
Leptin as a Regulator of Energy Balance
The leptin receptor (with long and short isoforms) is a
member of the cytokine family of receptors and is expressed
in a variety of tissues including the hypothalamic nuclei (7).
Neurons in the arcuate, ventromedial, and dorsomedial hy-
pothalamic nuclei that are sensitive to leptin express neu-
ropeptides/neurotransmitters that are associated with central
regulation of energy balance (2). Leptin receptor mutations
cause early onset obesity in rodents and occur in humans,
but are very rare (2, 8).
Leptin is regulated by the status of fat storage, with
1
To whom requests for reprints should be addressed at R.R. Kraemer, Department of
Kinesiology and Health Studies, Southeastern Louisiana University, SLU 10845,
Hammond, LA 70402. E-mail: rkraemer@selu.edu
1535-3702/02/2279-0701$15.00
Copyright © 2002 by the Society for Experimental Biology and Medicine
LEPTIN AND EXERCISE 701
larger adipocytes containing more leptin than smaller ones
in the same individual (9). Nutrition-related control of leptin
has been suggested to be partially regulated by insulin. It
has been demonstrated that leptin expression occurs after
elevation of insulin in response to feeding (10), and a de-
cline in leptin levels follows reduction in insulin during
fasting (11). Some early studies reported no acute effect of
eating on leptin concentrations, but later studies that con-
trolled for fasting demonstrated that meals and insulin
acutely affect leptin concentrations (12). Other hormones
associated with the regulation of leptin that are altered by
exercise include glucocorticoids, growth hormone, and cat-
echolamines (13, 14). Growth hormone and cortisol have
been shown to promote leptin production (15, 16), whereas
catecholamines inhibit leptin production (17, 18).
Leptin as a Regulator of Reproductive Function
Gender influences leptin levels and may affect the sta-
tus of reproduction. Leptin levels are higher in females than
in males (19, 20). Higher leptin levels in females have been
attributed to a number of factors, including stimulation by
estrogens, inhibition by androgens, and fat-depot differ-
ences in leptin expression (2, 21). Interestingly, Maccario et
al. (22) have reported that gender differences in growth
hormone and leptin are abolished after a 36 hr fast. In-
creases in circulating levels of leptin are associated with the
onset of menarche in girls (23). Leptin levels in normally
cycling females are greater than in young males, even after
accounting for differences in adiposity (19), and this holds
true for males and females of older ages (24–26). Elevated
leptin levels in hypogonadal males are reduced when tes-
tosterone is administered (27). Moreover, in vitro experi-
ments using newly developed human adipocytes have dem-
onstrated that testosterone and dihydrotestosterone, its bio-
logically active metabolite, both suppress leptin secretion
into the culture medium by as much as 62% (16). Finally,
leptin expression is greater in subcutaneous than in visceral
adipose tissue, and females have a greater amount of sub-
cutaneous fat than males (2).
Effects of Exercise on Leptin
There are many investigations that have examined the
effects of exercise on leptin. There are several reasons why
leptin responses and adaptations to exercise may have im-
portant ramifications: exercise is known to effectively re-
duce obesity (fat mass), thus, if leptin levels are affected,
this may provide some explanation of how exercise affects
obesity; exercise (specifically, caloric expenditure leading
to energy imbalance) may lead to reproductive dysfunction
(28), and because leptin is associated with reproductive
function, exercise-induced alterations in leptin may eluci-
date the mechanisms explaining effects of exercise on re-
production, such as the condition of exercise-induced amen-
orrhea; and exercise alters concentrations of certain hor-
mones that may alter leptin concentrations, including
insulin, cortisol, catecholamines, estrogen, testosterone,
DHEA, and growth hormone (29–36). The ensuing sections
will include a review of leptin responses to short-term ex-
ercise, followed by a discussion of responses to long-term
exercise and training studies.
Acute Exercise and Leptin
Short-Term (<60 min) Exercise. Most studies that
have investigated effects of short-term exercise on leptin
have shown reductions or no change in leptin concentra-
tions. Elias et al. (37) reported a decline in leptin concen-
trations in males (age 18–55) after a graded treadmill exer-
cise test to exhaustion. The authors suggested that the de-
cline may be associated with elevated production of
nonesterfied fatty acids during exercise, which have previ-
ously been shown (38) to be inversely correlated with leptin
levels. A control trial was not conducted in this study to
determine whether diurnal changes accounted for observed
reductions.
Fisher et al. (12) administered a standardized meal to
subjects and observed increases in leptin during 41 min of
cycling at 50% of the cycling intensity of VO
2max
.This was
followed by a reduction in leptin concentrations during re-
covery that increased to control values after 2 hr. Cortisol
and epinephrine concentrations rose sharply during exer-
cise, and epinephrine declined quickly after the exercise.
Cortisol stimulates leptin expression, whereas epinephrine
and norepinephrine inhibit leptin expression. It was hypoth-
esized that large increases in cortisol concentrations would
stimulate increases in leptin levels, but only a weak rela-
tionship between leptin and cortisol was found. However,
the nutrient factors, glucose, insulin, and glucose × insulin,
explained 86% of the variance in final leptin levels. The
authors reported normalized leptin concentrations (using se-
rum protein content) for plasma volume shifts and con-
cluded that the short-term exercise-related changes are due
to alterations in hemoconcentration rather than to leptin
mass.
We have demonstrated that 30 min of exercise at 80%
of VO
2max
is associated with reduced leptin concentrations
in postmenopausal females regardless of whether they are
on or off hormone replacement therapy (HRT), but the re-
ductions were due to the circadian rhythms of leptin as
determined from control trial samples from the same sub-
jects (14). Cortisol and growth hormone, both hormones
that affect leptin concentrations, increased in these females
in response to exercise (29, 34). It is possible that under
certain exercise conditions, hormones that stimulate leptin
expression (e.g., cortisol) are countered by hormones that
inhibit leptin secretion (e.g., epinephrine), such that no al-
teration from these regulators is evident.
Weltman et al. (39) reported that 30 min of exercise at,
above, and below lactate threshold, an index of accelerated
metabolism and exercise intensity, did not alter leptin con-
centrations in young males during exercise or recovery (3.5
hr postexercise) compared with control values. In this study,
702 LEPTIN AND EXERCISE
exercise intensity was not a factor in affecting leptin re-
sponses in young men.
We recently reported significant increases in leptin re-
sponses to a graded exercise test to exhaustion in young
adolescent (14–16 years) runners over the course of a short
track season (32). The increases in the study may have been
due to hemoconcentration, which would have presented
higher concentrations of leptin to the leptin receptors.
Thus, short-term (<60 min) exercise studies suggest
that leptin production is not acutely effected by short-term
exercise, regardless of exercise intensity, in healthy males
and females. Reported reductions or increases can be attrib-
uted to circadian rhythms or hemoconcentration. It remains
to be determined how hormones and metabolites that appear
to stimulate (e.g., cortisol, insulin, and glucose) or inhibit
(e.g., epinephrine and norepinephrine) leptin work together
to prevent decline under some conditions but not in other
conditions (12). Further work is also required to determine
whether acute increases produced by hemoconcentration
produce any effect on tissues. The absence of any reduction
in leptin reported in short-term exercise study may be due to
the limited energy expenditure of these exercise bouts or the
protocol of these studies that excluded prolonged post ex-
ercise blood sampling (ⱕ4 hr postexercise). As will be
shown in the next section, when blood samples are collected
48 hr following long-term exercise, reductions in leptin are
found.
Long-Term (≥ 60 min) Exercise. As for short-term
exercise, long-term exercise studies have typically revealed
no change or a decline in leptin following exercise. Racette
et al. (40) measured arteriovenous differences in leptin con-
centrations from abdominal adipose tissue during 60 min of
cycle ergometry exercise, and reported no change in leptin.
Samples were not collected during recovery. Torjman et al.
(41) measured leptin concentrations following 60 min of
treadmill exercise at 50% of VO
2max
. After leptin concen-
trations were corrected for hemoconcentration, they found
no effect on leptin concentrations during a 4-hr recovery
period. Trained males completing 60 min of running at ap-
proximately 70% of VO
2max
showed leptin concentrations
that were significantly lower 48 hr after the exercise com-
pared with before, immediately after, and 24 hr after the
exercise (42). The leptin responses did not appear to be
related to changes in insulin or glucose concentrations.
Blood samples were also collected from the same subjects
after a short-term maximal exercise test, and leptin levels
did not decline immediately after, or 24 or 48 hr postexer-
cise. Essig et al. (43) reported lower leptin concentrations in
trained males 48 hr after but not 0 and 24 hr after two
separate exercise tests, an 800- and 1500-kcal treadmill run.
The authors speculated that alterations in the leptin stimu-
lators, growth hormone, cortisol, and insulin, as well as the
leptin inhibitors testosterone, epinephrine, and norepineph-
rine, may have affected leptin concentrations. The above
studies demonstrate that long-term exercise induces lower
leptin concentrations, which is not seen at shorter intervals
of recovery. Moreover, it suggests a need for determining
the exact point at which delayed leptin reduction occurs.
This would require greater sampling frequency than 24 and
48 hr.
Leptin responses to much longer durations of exercise
have been examined. One of the first such studies investi-
gated leptin responses of well-trained male runners to a
20-mile treadmill run at an intensity of 70% of VO
2max
(44).
No change in leptin concentrations were found after this
extreme bout of exercise. One of the limitations of the study
(and other studies to follow) was an infrequent blood sam-
pling protocol. Duclos et al. (38) compared a 4-hr resting
trial to a 2-hr run/2-hr resting trial in subjects that consumed
a standardized meal 2-hr before exercise to control for fast-
ing. There was a 30% reduction in postexercise resting lep-
tin concentrations. The investigators reported significant in-
verse correlations between leptin and glycerol as well as
free fatty acid levels, but no correlation with cortisol. Tu-
ominen et al. (45) used a 4-hr euglycemic insulin clamp and
muscle biopsies to study the effects of 2 hr of treadmill
exercise at 75% of VO
2max
. Exercise reduced leg muscle
glycogen by 32% compared with the control clamp trial, and
there was a 34% reduction in leptin concentrations. Serum
leptin concentrations were reduced by glycogen-depleting
exercise and were increased during a hyperinsulinemic
clamp. Leptin concentrations correlated directly with serum
insulin, cortisol, and triglycerides, and inversely with
growth hormone concentrations. The authors concluded that
leptin is associated with factors that govern fuel homeostasis.
Leal-Cerro et al. (46) controlled for circadian variations
and reported a small reduction in leptin levels in males
following a marathon (∼ 26 miles, ∼ 2800 kcals) and sug-
gested the actual reduction was greater than measured re-
duction because hemoconcentration occurred during the
marathon. The authors concluded that large changes in en-
ergy expenditure may regulate serum leptin concentrations.
Karamouzis et al. (47) studied leptin responses following a
25 km sea swim and reported that lower leptin concentra-
tions were associated with an 81% increase in plasma neu-
ropeptide Y which is associated with energy regulation.
Landt et al. (48) reported an 8% reduction in fasting
serum leptin concentrations following 2 hr of exercise that
included cycling at ∼ 75% of VO
2max
and culminated with
five 1-min cycle sprints. The reduction was similar to that of
a control group that fasted an identical time period, attrib-
uting the exercise related decline to diurnal reduction. The
same authors studied pre- and postleptin concentrations that
were obtained from runners who completed an ultramara-
thon, a 101-mile race (average exercise time ∼ 35 hr), and
demonstrated a 32% decline in leptin. The authors sug-
gested that the large reduction in leptin in the ultramara-
thoners was due to energy imbalance and that leptin may
serve as an important signal of energy imbalance, but only
at imbalance extremes.
In a well-controlled study by Hilton and Loucks (49),
LEPTIN AND EXERCISE 703
effects of energy imbalance on leptin, energy intake and
expenditure were carefully controlled in sedentary and ex-
ercising females, and blood sampling was completed over a
24-hr period to determine whether leptin circadian rhythm
was altered. The authors found that low energy availability
suppresses the 24-hr mean and amplitude of the diurnal
rhythm of leptin; however, exercise had no impact on the
diurnal rhythm of leptin in young females except for its
effect on energy balance. The authors concluded that the
diurnal rhythm of leptin depended on energy or carbohy-
drate availability. Previous studies have shown that secre-
tion of leptin was inversely proportional to carbohydrate in
the diet (50). The authors suggested that there is a reduction
threshold of energy availability to change the dynamics of
the diurnal rhythm of leptin. These observations suggest
that leptin levels may be effected by the total exercise en-
ergy expenditure from increased metabolism during exer-
cise as well as during recovery from exercise.
In an energy balance study of young males, van Agel-
Leijssen et al. (51) showed that exercise decreased peak and
average 24-hr leptin concentrations and that high physical
activity in a positive energy-balanced state increases the
amplitude of the 24-hr leptin concentrations. However, the
negative energy-balance condition did not affect 24-hr lep-
tin concentrations, initially suggesting a gender difference
in effects of energy balance when examined with regard to
the study of females by Hilton and Loucks (49). However,
it should be noted that the there was a 28% negative energy
condition in this study of males compared with a 78% re-
duction in energy intake in the study of females (49), which
likely explains the different results.
Koistinen et al. (52) examined the effect of feeding
before 3 hr of cycling exercise on leptin concentrations in
healthy and type I diabetic males. The authors concluded
that exercise may lower circulating leptin concentrations,
however, the small reduction may be counterbalanced by
feeding or an elevation in cortisol concentrations.
To summarize long-term (ⱖ60 min) exercise effects on
leptin, a reduction in leptin concentrations reported from 1
to 2 hr of running or cycling has been attributed to diurnal
reduction in circulating leptin, independent of exercise.
Very long bouts of exercise are more likely to reduce leptin
levels, which is probably due to disruption of energy bal-
ance. The seminal work by Hilton and Loucks (49) and van
Agel-Leijssen et al. (51), which represent the best well-
controlled studies for energy balance to date, provide clear
evidence of the importance of careful control for energy
balance in leptin and exercise studies, and thus impinge on
all work in this area. Exercise that produces a sufficient
energy imbalance (kilocalorie intake versus kilocalorie ex-
penditure) suppresses 24-hr mean and amplitude of the di-
urnal rhythm of leptin. Suppression of leptin concentrations
may be counterbalanced by feeding. This appears to explain
consistent reductions reported in leptin concentration after
extreme bouts of exercise such as marathons or ultramara-
thons. In addition, long-term exercise (ⱖ60 min) appears to
be associated with reduced leptin concentrations 48 hr after
exercise. The mechanism explaining these observations re-
mains to be elucidated.
Leptin Levels Following Exercise Training
Short-Term (<12 weeks) Training. A number of
studies have investigated the effects of training on leptin
concentrations. These studies have tended to report either no
effect of training on leptin concentrations with short-term
training, unless the training was associated with fat loss, or
a reduction in leptin levels beyond that accounted for by
reduction in fat mass in long-term training studies. Hou-
mard et al. (53) studied the effects of short-term (7 con-
secutive days) aerobic training (1 hr/day at 75% VO
2max
)on
leptin concentrations and insulin action in healthy young
and older males. Although the training improved insulin
sensitivity (determined by an i.v. glucose tolerance test),
leptin concentrations were not effected.
Dirlewanger et al. (54) measured leptin concentrations
after 3 days of no exercise and an isoenergetic diet; exercise
(cycling for 30 min at 60% of VO
2max
) twice daily with the
same caloric intake as trial 1; and exercise with dietary
intake to cover exercise energy expenditure. There were no
changes in leptin concentrations in any of the trials. The
authors reported that plasma leptin is unaltered by exercise
or small changes in energy balance over short periods of
time.
We have studied the effects of a 9-week training pro-
gram on leptin concentrations of middle-age obese females
(55). Training consisted of 3–4 days of exercise including
20–30 min of step aerobics 2 days per week and tread-
mill running or stationary cycling on additional days. Al-
though cardiorespiratory fitness levels (VO
2max
) increased
after training, there were no changes in fat mass or leptin
concentrations.
In a study of adolescent female runners, we measured
resting and postmaximal exercise leptin concentrations over
the course of a short track season (32). Resting leptin levels
were not altered over the 7 weeks, nor were the acute re-
sponses to intense exercise.
Halle et al. (56) studied obese males with type 2 dia-
betes and reported that 1 month of cycling exercise com-
bined with a low-caloric diet resulted in reduced body
weight and leptin concentrations. The lower leptin concen-
trations were associated with reduced cholesterol and tri-
glyceride levels, which was independent of improvements
in glucose control. The authors suggested that the relation-
ship between leptin and insulin might be indirectly due to
elevated serum triglycerides or fatty acid concentrations. In
a 6-week study of 50 sedentary subjects with type 2 diabe-
tes, exercise training (low-intensity walking and cycling)
coupled with diet therapy led to lower leptin concentrations
independent of changes in body composition, insulin, or
glucocorticoids (57). A group on diet therapy without ex-
ercise did not show reductions in leptin concentrations.
704 LEPTIN AND EXERCISE
Long-Term (≥ 12 weeks) Training. Hickey et al.
(20) reported significant reductions in fasting leptin levels
in young females (mean age 29 y), but not young males
(mean age 27 y) after aerobic exercise training, 4 days/wk,
30–45 min/day, for 12 weeks. These leptin reductions in
females occurred in the absence of significant alterations in
fat mass and results suggest that training has a greater effect
on circulating leptin levels in females than in males. A study
of obese children (24 girls and 10 boys) reported that after
correction for loss of fat mass, leptin concentrations were
lowered after 4 months of exercise training (exercise on
machines and playing games), but that levels increased in a
subsequent 4-month period without physical training (58).
The authors speculated that the reduction in leptin concen-
trations were caused by changes in energy balance.
Middle-age obese males were trained (low to moderate
exercise intensity, three to four times per week) and main-
tained a very low-energy diet for 4 months (59). The authors
concluded that leptin concentrations were reduced from
aerobic exercise training independent of changes in body fat
and plasma insulin concentrations.
Okazaki et al. (60) examined the effects of mild aerobic
exercise (50% VO
2max
) and personal diet counseling for 12
weeks on fat loss and leptin concentrations in obese and
nonobese middle-aged sedentary females. The ratio of lep-
tin concentrations to fat mass and to body mass index (BMI)
was reduced after the training. The authors suggested that
reduced leptin concentrations were probably due to weight
reduction and some unknown factor(s).
A large cohort of males with metabolic syndrome (el-
evated blood lipids, blood pressure, body composition, etc.)
were divided into four treatment groups: diet, diet and ex-
ercise, exercise, and control (61). Exercise consisted of 60
min of fast walking, jogging, and circuit training three times
per week for 1 year. The authors found that both diet and
exercise were associated with reduced leptin concentrations
beyond the reduction expected from changes in body fat. It
was speculated that an improvement in insulin sensitivity
could alter leptin concentrations.
Thong et al. (62) examined the independent effects of
exercise and weight loss on sedentary males with upper
body obesity. Subjects trained for 12 weeks with brisk walk-
ing or jogging. Alterations in leptin correlated with changes
in both total and subcutaneous adipose tissue. The authors
reported that independent of its effect on energy balance,
exercise has little effect on leptin secretion.
Males and females with normal body composition were
studied in a progressive training protocol of cycling three
times per week for 20 weeks (63). Subjects were adminis-
tered a mild exercise test before and after training in which
they cycled for 10–12 min at a low intensity (50 W) and
progressed to exhaustion. After adjusting for fat mass loss,
resting leptin levels were not altered from training, nor were
acute leptin responses to the exercise.
Noland et al. (64) measured leptin concentrations in
young male and female intercollegiate swimmers across a
competitive season. There were no changes in body fat for
the males, but there was a reduction for the females with
increased training volume. There were no changes in leptin
in either group despite the fat loss in females. The authors
speculated that no change in leptin with fat loss might be
due to training-induced increases in cortisol with intense
training.
Kohrt et al. (65) trained postmenopausal females on
and off (HRT) first for 2 months with flexibility exercises,
then 9 months with walking, jogging, and stair climbing.
Regardless of HRT treatment, there were no independent
effects of exercise on leptin levels other than the indirect
effect of fat loss. In a related nonexercise study, we reported
that when body composition is taken into account, estrogen
treatment, either in young females receiving estrogen-
progestin oral contraceptives or in postmenopausal females
who are receiving HRT, does not affect serum leptin
concentrations (19).
Thus, short-term exercise training (ⱕ12 weeks) does
not affect leptin levels, with the exception of patients with
type 2 diabetes. Exercise training protocols that result in
reduced fat mass will lower leptin concentrations, hence,
most investigators have reported leptin concentrations after
accounting for fat loss. There are disparate findings con-
cerning long-term (>12 weeks) training studies, with a num-
ber of studies finding no effect of training on leptin con-
centrations other than effects induced by fat loss, and other
studies finding reductions in leptin concentrations after ac-
counting for fat loss. Exercise training-induced reductions
in leptin levels have been attributed to alterations in energy
balance, and glucoregulatory factors including improve-
ments in insulin sensitivity, lipid metabolism, and unknown
factors. Despite numerous studies and different protocols,
mechanisms responsible for leptin regulation remain to be
determined. Hormone replacement does not seem to affect
leptin adaptations to training. Patients with type 2 diabetes
show a reduction in leptin with long-term training and seem
to be more sensitive to training-induced leptin adaptations
than other populations.
Effects of Resistance Exercise on Leptin
There are three prospective studies that have examined
the effects of resistance exercise (weight training) on leptin.
Kanaley et al. (66) demonstrated a reduction in plasma lep-
tin levels in type 2 diabetic patients ∼ 24 hr following lower
and upper body resistance exercises, whereas normal sub-
jects did not show the same decline. The authors speculated
that a reduction in glucose availability to adipocytes in the
diabetic patients may have produced the different response.
They also found no effect of chronic resistance training on
leptin levels.
In a recent, carefully controlled study, Nindl et al. (67)
measured leptin concentrations overnight following 50 total
sets of resistance exercise including squats, bench press, leg
press, and lat pull-down exercise. Leptin concentrations
were lower compared to the control trial at 3 hourly time
LEPTIN AND EXERCISE 705
points, 9, 12, and 13 hr following exercise. Estimated en-
ergy expenditure was considerable, averaging 856 kcal.
These data, coupled with previous studies (e.g., 42, 43)
suggest that exercise with energy cost ⱖ800 kcal produces
delayed leptin reduction, however it was documented much
earlier in this study compared with previous studies. The
authors demonstrated the importance of determining leptin
concentrations well after completion of the exercise.
Ryan et al. (68) studied effects of 16 weeks of resis-
tance training in obese postmenopausal females with and
without weight loss, on plasma leptin and insulin action.
The resistance training increased fat-free mass and resting
metabolic rate in combined data from both groups. Leptin
concentrations declined by 36% in the group that lost
weight. Changes in leptin levels were not related to alter-
ations in resting metabolic rate or plasma catecholamines.
However, the authors speculated that weight loss in the
resistance training/weight loss subjects may have mediated
increases in insulin action reported in the study.
Suggestions for Future Research
Although many studies have been published on the ef-
fects of exercise on leptin, numerous questions remain to be
answered. There is a need to better define the relation of
adiposity in both genders to leptin responses and adapta-
tions to exercise. Future studies should also compare the
effects of negative energy balance on leptin levels in males
and females, and should better describe the effects of dif-
ferent degrees of fasting on leptin response to exercise. The
work by Hilton and Loucks (49) and van Agel-Leijssen et
al. (51), provide clear evidence of the importance of careful
control for energy balance in future leptin and exercise stud-
ies. The evidence that leptin levels decline 9 hr after resis-
tance exercise of substantial kcal expenditure (long-term)
and 48 hr after long-term aerobic exercise suggests that
there is a delayed reduction in leptin that may be due to
energy imbalance. Thus, in order to determine the true dy-
namics of exercise-induced leptin responses, future studies
should examine leptin concentrations for much longer pe-
riods after exercise. These studies should involve stringent
controls for energy balance and more frequent sampling.
Improved studies are also needed to examine other endo-
crine factors that may impinge on leptin regulation during
exercise. Many studies have examined insulin and cortisol,
but they leave other important regulatory factors unstudied.
The use of hormone antagonists might be helpful in deter-
mining individual roles for specific hormones that regulate
leptin. It would also be useful for future studies to examine
the independent effect of alterations in lipid metabolism and
glucose control on leptin concentrations to elucidate the
mechanisms that explain the observed reductions in leptin
from acute and chronic exercise. Finally, there is a need for
more investigations to compare the effects of aerobic versus
resistance exercise on leptin.
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