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Clinical Science (2001) 101, 359–365 (Printed in Great Britain)
Difference in leptin response to a high-fat meal
between lean and obese men
P. IMBEAULT*, E. DOUCET*, P. MAURIE@ GE*†, S. ST-PIERRE*, C. COUILLARD†,
N. ALME; RAS†, J.-P. DESPRE; S†‡ and A. TREMBLAY*
*Division of Kinesiology, Department of Social and Preventive Medicine, Laval University, Ste-Foy, Que! bec, Canada G1K 7P4,
†Lipid Research Center, Laval University Medical Research Center, Ste-Foy, Que! bec, Canada G1V 4G2, and ‡Que! bec Heart
Institute, Laval Hospital Research Center, Ste-Foy, Que! bec, Canada, G1V 4G5
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The aim of this study was to compare the leptin responses to a high-fat meal in lean and obese
men, and to investigate whether the net leptin response (area under the incremental curve) after
the meal was related to the thermic effect of food (TEF). Blood samples were collected after an
overnight fast and every 2 h for 8 h after a high-fat breakfast (60 g of fat/m2 body surface area) in
12 lean and 12 obese men for determination of glucose, insulin and leptin. The TEF was calculated
as postprandial energy expenditure minus fasting energy expenditure, as measured by indirect
calorimetry. Fasting plasma glucose levels were similar in lean and obese men, and increased in
the same way after the meal. Fasting and postprandial plasma insulin concentrations were
significantly greater in obese than in lean men (P 0.01 and P 0.05 respectively). Accordingly,
obese men showed a significantly higher net insulin response than lean subjects (P 0.001).
Fasting plasma leptin levels were greater in obese than in lean men (P 0.001). After the meal,
plasma leptin increased significantly in lean men, whereas it decreased in obese men (group by
time interaction, P 0.01). The net response of leptin was greater in lean than in obese men, but
this did not reach statistical significance (P l 0.07). Moreover, the TEF was similar in the two
groups. No significant relationship was observed between either the net insulin response or the
net leptin response after the high-fat meal and the TEF of lean subjects (k0.05 r 0.31). In
obese men, the net response of insulin was correlated significantly with TEF (r l 0.70, P 0.05),
whereas the net response of leptin was not (r l k0.40). These results suggest that obesity is
related to an impaired regulation of leptin by insulin, since leptin levels increased in lean men but
decreased in obese men following a high-fat meal. Moreover, the fact that the postprandial leptin
responses of both lean and obese men were not significantly related to the TEF suggests that the
ob gene product is probably not acutely involved in the control of this energy expenditure
component in humans.
INTRODUCTION
There is now convincing evidence that leptin acts as a
signal reflecting acute variation in energy balance, rather
than as an ‘ adipostat ’ [1]. Indeed, several studies have
shown that plasma leptin levels decrease much more than
would be expected on the basis of body fat loss [2,3]. The
same phenomenon is observed with refeeding, as leptin
increases in a disproportionate manner when compared
with the increase in adipose tissue mass [4]. Taken
Key words: indirect calorimetry, leptin response, obesity, postprandial insulin.
Abbreviation: TEF, thermic effect of food.
Correspondence: Dr Angelo Tremblay (e-mail angelo.tremblay!kin.msp.ulaval.ca).
# 2001 The Biochemical Society and the Medical Research Society
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P. Imbeault and others
together, these findings suggest that the ability of adipose
tissue to produce leptin is affected by a limited or
increased energy availability, and that leptin possibly
promotes a compensatory change in food intake and\or
energy expenditure before major alterations occur in fat
reserves.
Several studies have investigated the short-term effect
of food intake on postprandial leptinaemia in humans,
but discordant results have been reported. Some investigators reported a significant response of leptin concentration to a single meal test [5–8], whereas others did
not [2,9–12]. Possible explanations for these discrepancies
are the different types of meals consumed, as well as
differences in the timing of the postprandial blood
sample. Another confounding factor that may modulate
the leptin response to food could be the subjects ’
characteristics, since plasma insulin, which is known to
modulate leptin [13], differs significantly between lean
and obese individuals in the postprandial state [14].
However, no study has yet examined whether postprandial leptin levels differ between lean and obese
subjects. Therefore we first investigated the response of
leptin to a high-fat meal in lean and obese men. We also
examined whether the thermic effect of food (TEF) is
related to the net response of leptin to food intake, as
leptin has been found to increase energy expenditure in
both non-obese [15] and ob\ob mice [15–17].
METHODS
Subjects
Twelve healthy lean and twelve obese men were recruited
through the media, and gave their written informed
consent to participate in the study, which was approved
by the Laval University Medical Ethics Committee. Men
with a body fat percentage (estimated by hydrodensitometry) of 25 % were considered as lean, whereas a
body fat percentage of 30 % defined the obese group.
All individuals underwent a medical evaluation by a
physician, which included a medical history. Subjects
with cardiovascular disease, diabetes mellitus or endocrine disorders, or those on medication that could have
influenced triacylglycerol metabolism (β-blockers, antihypertensive drugs, etc.), were excluded from the study.
All participants were sedentary (no more than two
continuous exercise sessions of 30 min per week), nonsmokers and moderate alcohol consumers. None had
recently been on a diet or involved in a weight-reducing
program, and their body weight had been stable during
the last 6 months prior to the study.
Experimental protocol
The subjects arrived at the laboratory at 06.45 hours.
After voiding, the subjects rested comfortably in the
# 2001 The Biochemical Society and the Medical Research Society
supine position for 15 min, whereafter resting metabolic
rate was measured for 15 min. Immediately after this, an
intravenous catheter was inserted into a forearm vein and
a blood sample was taken before the breakfast. The
subjects were then offered a high-fat breakfast that was
ingested within a maximum period of 30 min. After the
meal, gas exchange was measured hourly (15 min measurement periods), and blood samples were taken every
2 h for an 8 h period. During the postprandial measurements, subjects were allowed to watch light entertainment movies. During the short breaks, the subjects were
allowed to sit, walk quietly and go to the washroom.
Total body fat and regional fat distribution
Body density was determined by the underwater weighing technique, and percentage body fat was derived from
body density [18]. Pulmonary residual volume was
measured using the helium dilution method [19]. Fat
mass was calculated as total body weight minus fatfree mass. Computed tomography (CT) was performed
with a Somatom DRH scanner (Siemens, Erlangen,
Germany), according to the methodology described
previously by Sjo$ stro$ m et al. [20]. Briefly, subjects were
examined in the supine position with both arms stretched
above the head. CT scans were performed at the
abdominal level (between the L4 and L5 vertebrae), using
an abdominal scout radiograph to establish the position
of the scans to the nearest millimetre. Total adipose tissue
areas were calculated by delineating the abdomen with a
graph pen and then computing adipose tissue surfaces
with an attenuation range of k190 to k30 Hounsfield
units [21]. Abdominal visceral adipose tissue area was
measured by drawing a line within the muscle wall
surrounding the abdominal cavity. The abdominal subcutaneous adipose tissue area was calculated by subtracting the visceral adipose tissue area from the total
abdominal adipose tissue area.
Oral lipid tolerance test
All subjects were instructed to abstain from prolonged
and vigorous physical activity for 2 days before the test
meal. After a 12 h overnight fast, each participant was
given a breakfast containing 60 g of fat\m# body surface
area, as described previously [22]. This approach was
chosen to represent the energy expenditure of each
individual over the 8 h of the experimental session. The
test meal had an energy content (meanpS.D.) of 7464p
167 kJ (1784p40 kcal) and 8485p167 kJ (2028p40 kcal)
for the lean and obese men respectively, and consisted of
64 % of energy as fat, 18 % of energy as carbohydrate and
18 % of energy as protein. The Canadian Nutrient File
[23] was used in the calculation of the energy and nutrient
composition of the breakfast. The meal was composed of
eggs, cheese, toast, peanut butter, peaches, whipped
cream and milk, and was well tolerated by all subjects.
Postprandial leptin response and obesity
Subjects took approx. 25 min to consume the meal,
beginning between 07.30 and 07.45 hours. After the meal,
subjects were not allowed to eat for the next 8 h, but were
given free access to water.
program (SAS Institute Inc., Cary, NC, U.S.A.) adapted
for Macintosh computers.
RESULTS
Energy expenditure
Resting energy expenditure was measured by indirect
calorimetry after a 12 h overnight fast. After a 15 min
resting period, expired gases were collected over
15 min through a mouthpiece while the nose was clipped.
After the meal, respiratory gas exchanges were measured
for 15 min periods every 1 h over the 8 h period. TEF was
calculated as the the total increase in caloric expenditure
above resting energy expenditure. Oxygen and carbon
dioxide concentrations were determined by non-dispersive IR analysis (Uras 10 E ; Hartmann & Braun),
and pulmonary ventilation was assessed with an S-430A
measurement system (Ventura) which has been validated
previously by Linnarsson et al. [24]. The Weir formula
[25] was used to determine the energy equivalent of
oxygen volume.
Concentrations of glucose, insulin, leptin
and non-esterified fatty acids
Plasma glucose levels were determined using the glucose
oxidase assay [26] (Sigma, St. Louis, MO, U.S.A.). Plasma
insulin concentrations were measured by a commercial
double-antibody RIA (Linco Research, St. Louis, MO,
U.S.A.) that shows little cross-reactivity ( 0.02 %) with
pro-insulin [27]. Plasma leptin levels were determined
with a highly sensitive commercial double-antibody RIA
(Linco Research) that detects relatively low leptin levels
(0.5 ng\ml) and does not cross-react with human insulin,
pro-insulin, glucagon, pancreatic polypeptide or somatostatin. Plasma non-esterified (‘ free ’) fatty acid levels were
measured by using a colorimetric method [28].
Statistical analyses
Student’s t test was used for comparisons between lean
and obese groups. ANOVA for repeated measures was
used to verify differences between groups (lean and
obese) in plasma insulin, glucose and leptin concentrations, as well as energy expenditure. Identification of a
significant group by time interaction led to further
analysis of a simple main effect for group. The level of
significance was set at P 0.05. The areas under the
incremental curve or the net responses for the 8 h
measurement periods were calculated separately for each
subject as the difference between the integrated area of
the response curve and the rectangular area determined
by the basal values. Negative areas were included.
Associations between two variables were quantified by
Pearson’s product–moment correlation coefficients. All
analyses were performed using the Jump version 3.2.2
Physical characteristics of subjects are presented in Table
1. Lean and obese men were of similar age. As expected,
obese men were characterized by greater body weight,
body mass index, fat mass, and subcutaneous and visceral
abdominal adipose tissue areas than lean individuals (P
0.001). No difference was found for fat-free mass between
the groups.
Figure 1 shows plasma glucose, insulin and leptin
concentrations before and after the high-fat meal in lean
and obese subjects. Fasting plasma glucose concentrations were similar in the two groups (Figure 1A). A
significant time effect for glucose was observed in both
groups (P 0.001). However, no difference in plasma
glucose levels was found between groups during the
meal. Also, the net response of glucose was similar in lean
and obese men.
On the other hand, fasting plasma insulin levels were
greater in obese than in lean subjects (P 0.01) (Figure
1B). A significant group by time interaction (P 0.05)
was observed for plasma insulin levels, revealing that
obese men had a significantly greater postprandial increase in insulin level than lean subjects. Accordingly,
obese men showed a significantly higher net response
than lean subjects for insulin (P 0.001).
Fasting plasma leptin levels were significantly higher in
obese than in lean men (P 0.001) (Figure 1C). Moreover, the plasma leptin response pattern differed significantly between groups after the meal (group by time
interaction, P 0.01). Indeed, lean men showed a significant increase in plasma leptin levels after the meal,
whereas leptin concentrations decreased significantly in
obese subjects. The mean net response of leptin was
positive in lean subjects and negative in obese men, but
this difference fell short of statistical significance (P l
0.07). Postprandial levels of non-esterified fatty acids
Table 1
Physical characteristics of subjects
Data are meanspS.D. Significant differences between groups : *P
Parameter
Age (years)
Body weight (kg)
Body mass index (kg/m2)
Body fat ( %)
Fat mass (kg)
Fat-free mass (kg)
Abdominal adipose tissue area (cm2)
Subcutaneous
Visceral
Lean (n l 12)
0.001.
Obese (n l 12)
47p10
75p8
25p2
22p4
17p4
59p6
46p9
100p12*
33p4*
36p3*
37p6*
63p8
183p50
112p35
395p105*
210p85*
# 2001 The Biochemical Society and the Medical Research Society
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P. Imbeault and others
Figure 1
Plasma levels of glucose (A), insulin (B) and leptin (C) before and after a high-fat meal in 12 lean and 12 obese men
Data are meanspS.E.M. Bars represent the areas under incremental curves (net responses) of each group. (A) Significant main effect for time at P 0.001. (B)
Significant interaction between group and time at P 0.05 ; significant difference between groups at ‡P 0.001. (C) Significant interaction between group and
time at P 0.01 ; level of significance of difference between groups : &, P l 0.07.
Figure 2
Energy expenditure before and after a high-fat meal in 12 lean and 12 obese men
Significant main effects for group (P
0.001) and time (P
0.001). Bars represent the areas under incremental curves (TEF) of each group. Data are meanspS.E.M.
# 2001 The Biochemical Society and the Medical Research Society
Postprandial leptin response and obesity
Figure 3
men
Relationships between net insulin or net leptin response after a high-fat meal and the TEF in 12 lean and 12 obese
1 kcal l 4.184 kJ.
increased significantly in both groups (time effect, P
0.001), and were higher in the obese group (group effect,
P 0.05) (results not shown).
As expected, basal resting metabolic rate was significantly higher in obese than in lean men (P 0.001)
(Figure 2). In both groups, a significant increase in energy
expenditure occurred in response to the meal (time effect,
P 0.001). Energy expenditure was higher in obese than
in lean men over the meal (group effect, P 0.001), but
the TEF (net response of energy expenditure) was similar
in the two groups.
No significant relationship was observed between
either the net insulin or the net leptin response to the
high-fat meal and TEF in lean subjects (k0.05 r
0.31) (Figure 3). In obese men, the net response of insulin
was correlated significantly with TEF (r l 0.70, P
0.05), but the net response of leptin was not (r l k0.40).
DISCUSSION
The present study showed that the postprandial leptin
response over an 8 h period following a high-fat meal in
men differed significantly depending on the body com-
position. Indeed, lean subjects showed an increase in
postprandial plasma leptin levels, whereas leptin concentrations decreased in obese individuals. Despite these
divergent postprandial leptin responses, no difference
was observed in the TEF between the two groups studied.
Previous studies have demonstrated that plasma leptin
was increased by physiological insulin infusions in
humans [13]. Our results in lean individuals are concordant with this observation, since their plasma insulin
and leptin concentrations increased during the high-fat
meal. Noteworthy is the fact that the increase in leptin in
response to the test meal in lean men was delayed
compared with that of insulin. These results confirm
those of Dallongeville et al. [5], who showed that the
serum leptin response of healthy men to a fatty meal only
began to reach statistical significance 6 h after the meal.
To some extent, these results support the notion that the
postprandial leptin response could be a consequence of
the effect of insulin on adipocytes, as suggested previously [29]. Our study also revealed significantly reduced leptin production in obese men, despite the fact
that these subjects displayed significantly increased insulin secretion after the high-fat meal. This is concordant
with the findings of Pratley et al. [6], who showed that
# 2001 The Biochemical Society and the Medical Research Society
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P. Imbeault and others
plasma leptin concentrations in obese subjects fell by 8 %
below baseline 2–4 h after a mixed meal. A physiological
explanation for this observation is a proposed continuation in the decline of leptin from the previous
night’s acrophase [12]. Whether or not a longer postprandial period would have been required to observe a
rise in serum leptin levels in obese men is not known.
Although leptin has been found to increase energy
expenditure in ob\ob mice [15–17] and in non-obese mice
[15], such observations remain to be confirmed in
humans. In the present study, no significant relationship
was observed between the TEF and the net response of
leptin in either group of men. This observation thus
suggests that leptin does not modulate this component of
energy expenditure in humans. According to the current
literature, the contribution of the ob gene product to
human energy expenditure appears to be involved in the
fall in resting energy expenditure accompanying weight
loss. Indeed, Wadden et al. [30] observed that the decrease
in resting energy expenditure was correlated significantly
with changes in plasma leptin after 40 weeks of energy
restriction in obese women. We have also recently
reported that changes in resting energy expenditure of
obese men in response to weight loss were best predicted
by changes in plasma leptin, even after adjusting for
changes in body composition [31].
As expected, the obese group showed a greater insulin
response after the meal than lean subjects. Based on
previous studies showing that men with low insulin
sensitivity displayed an impaired TEF [32], it would have
been expected that obese men showed a lower TEF in
response to the high-fat meal. However, one should keep
in mind that hyperinsulinaemia with euglycaemia has
been shown previously to increase muscle sympathetic
nervous activity [33], a well-known predictor of energy
expenditure [34]. In this regard, the significant positive
relationship observed between the net insulin response
and diet-induced thermogenesis in obese men suggests
that insulin is an important factor involved in the control
of TEF. To some extent, these results re-emphasize the
notion that insulin exerts a regulatory role, promoting
the restoration of energy balance when one gains weight
[35].
In addition to the fact that leptin administration
increases energy expenditure in mice, there is also
evidence that the administration of the ob gene product
has an inhibitory effect on food intake [15–17]. In this
regard, it would have been interesting to verify whether
the different pattern of leptin responses observed in lean
and obese men after the high-fat meal influenced their
satiety and hunger ratings differently. One could suggest
that obese men might have felt more hungry or less full
than their lean counterparts, since they had reduced
leptin secretion following the meal. However, the association between leptin levels and hunger and satiety
seems to occur more on a long-term than on a short-term
# 2001 The Biochemical Society and the Medical Research Society
basis in humans. Indeed, some studies reported that
leptin is a physiological regulator of hunger during
energy deficit, since the greatest increase in hunger rating
coincided with the largest percentage fall in circulating
leptin levels in response to a moderate energy deficit in
women [36,37]. Moreover, postprandial hunger and
satiety ratings do not seem to be related to plasma leptin
levels following a meal, at least in lean men [7,8]. Further
studies should nevertheless be performed to examine
whether the different patterns of leptin response between
lean and obese individuals following a high-fat meal
could have a different impact on their appetite control.
In summary, lean and obese men presented different
patterns of leptin response over an 8 h period after the
consumption of a high-fat meal : lean men showed
increased leptin levels, whereas obese men displayed
decreased postprandial leptinaemia. Moreover, the absence of a significant relationship between the postprandial leptin response and TEF in both lean and obese
men suggests that this hormone is not acutely involved in
the regulation of this component of energy expenditure
in humans.
ACKNOWLEDGMENTS
We express our gratitude to Dr Gilles Lortie for medical
supervision of the subjects. Linda Drolet and Alfred
Breton-Pare! are also gratefully acknowledged for their
technical assistance. P. I. is the recipient of a Natural
Sciences and Engineering Research Council of Canada
fellowship. This research was supported by the Medical
Research Council of Canada and the Fonds FCARQue! bec.
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Received 16 January 2001/30 April 2001; accepted 11 June 2001
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