(1985 ravussin) short-term, mixed-diet overfeeding in man (no evidence for _22luxuskonsumption) (1)
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7/28/2019 (1985 Ravussin) Short-term, Mixed-diet Overfeeding in Man (No Evidence for _22luxuskonsumption) (1)
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249:E470-E477, 1985. ; Am J Physiol Endocrinol MetabE. Ravussin, Y. Schutz, K. J. Acheson, M. Dusmet, L. Bourquin and E. Jequierevidence for "luxuskonsumption"Short-term, mixed-diet overfeeding in man: no
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Short-term, mixed-diet overfeeding in man:
no evidence for “luxuskonsumption”
E. RAVUSSIN, Y. SCHUTZ, K. J. ACHESON, M. DUSMET, L. BOURQUIN,
AND E. JEQUIER
Institute of Physiology, University of Lausanne, CH-1005 Lausanne, Switzerland
RAVUSSIN, E. , Y. SCHU TZ, K. J. ACHESO N, M. DUSMET, L.BOURQUIN, AND E. J~QUIER. Short- term, dxed-diet ouerfeed-ing in man: no evidence for “ luxuhnsumption. “Am. J. Physiol.
249 (Endocrinol. Metab. 12): E4’70-E477,1985.-After 13 daysof weight maintenance diet (13,720 t 620 kJ/day , 40% fat, 15%protein, and 45% carbohydrate), f ive young men (71.3 t 7.1 kg,
181 t 8 cm ; means t SD) were ove rfed for 9 days at 1.6 t imes
their maintenance requirements ( i.e., +8,010 kJ/day ). Twenty-four-hour energy expenditure (24-h EE) and basal metab olicrate (BMR) were measured on three occasions , once after 10
days on the weight-maintenance diet and after 2 and 9 days of
overfeeding. Physical activity was monitored throughout thestudy, body composit ion was measured by underwater weighing,and nitrogen balance was assess ed for 3 days during the two
experimental periods. Overfeeding caused an increase in bodyweight averaging 3.2 kg of which 56% was fat as measured byunderwater weighing. After 9 days of overfeeding, BMR in-creased by 622 kJ/da y, which could explain one-third of the
increase in 24-h EE (2,038 kJ/day); the remainder was due tothe thermic effect of food (which increased in proportion withexces s energy intake) and the increased cost of physical activity,
related to body weight gain. This s tudy show s that approxi-mately one-quarter of the exces s energy intake was dissipatedthrough an increase in EE, with 75% being s tored in the body.
Under our experimental condit ions of mixed overfeeding inwhich body composit ion measurem ents were combined withthose of energy balance, it was possible to account for all of theenergy ingested in exce ss of maintenance requirements.
twenty-four-hour energy expenditure; indirect calor imetry;physical activity; thermic effect of food
AT THE BEGINNING of the century, Neumann (16) ob-
served that the increase in body weight, in response to
hypercaloric diets, was not proportional to the excessenergy ingested. To explain this discrepancy he hypoth-
esized that some of the energy ingested in excess ofnormal requirements was dissipated as heat or “luxus-
konsumption.” This concept was revived later by Miller
et al. (15) and was supported by the findings of theVermont studies where it was observed that lean volun-
teers who gained weight while overeating required 50%
more energy to maintain their new body weights thantheir previous maintenance intake (29). However, con-
troversy stil l exists, because Glick et al. (10) failed tofind an increase in energy expenditure (EE) in response
to overfeeding and others who have observed th is phe-
nomenon deny that it is due to luxuskonsumption (17).
Furthermore, Forbes (6) recently reexamined Neumann’s
resul ts and noticed that h is body weight was influenced
by energy intake (EI) and changed in a totally predictable
manner. Webb (31)has proposed a form of unmeasuredenergy, but Garrow (9) has claimed that “the techniques
for measuring energy balances are sufficiently inaccurate
to allow for these apparent errors in energy balancestudies.”
Most of the cited studies were designed to investigate
the effect of overfeeding on basal metabolic rate (BMR),physical activity, the thermic effect of a meal, and the
cost of physical activity. However, total 24-h EE duringoverfeeding has rarely been measured (1, 3, 26, 32).Therefore this study was undertaken, by using a respi-
ration chamber, to measure 24-h EE during weight main-tenance and after 2 and 9 days of overfeeding at 160% of
weight maintenance EI. BMR, sleeping metabolic rate,
spontaneous daily physical activity, and the thermiceffect of the meals were also measured. This study sug-
gests that all the excess EI is accounted for by an increasein energy stores and that the increase in total EE can be
explained by an increase in BMR in relationship with
the increase in fat-free mass (FFM), an increased thermiceffect of food proportional to the excess EI, and an
increased cost of physical activity related to the bodyweight gain.
METHODS
Subjects. Five healthy male subjects with an average
age of 24 yr (range 22-27 yr), height 181 cm (range 172-190 cm), weight 71.3 kg (range 65.3-83.5 kg), percent
body fat 14.6% (range 9.3-23.4%), and body mass indexes
[wt (kg)/ht2 (m2)] of 22.2, 21.8, 22.5, 23.9, and 19.0volunteered for the study after reading a detailed account
of the protocol and discussing it with the investigators.The five subjects were known to have maintained their
body weight essential ly constant over 2 yr before thestudy. Besides having no family history of diabetes mel-
litus or obesity, the subjects were found to be healthy bya full medical examination before being considered for
the experiment. None of the subjects were smokers and
none were taking any medication before or during theexperiment. The protocol had previously been reviewed
and accepted by the hospital ethical committee.
Experimental protocol. Basically the protocol consistedof studying the subjects at the end of a 2-wk period
during which their body weights had been maintained
E470 0193-1849/85 $1.50 Copyright 0 1985 the American Physiological Society
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SHORT-TERM, MIXED-DIET OVERFEEDING IN MAN E471
Day
(MJ)
Diet
Body weight
Body composition
Activity indexes
Urine collections
24 E E + BMR
1 ; I
cl
r .
0l 0
FIG. 1. Experimental design. EE, energy expenditure; BM R, basalmetabolic rate.
TABLE 1. Mean daily energy and nutrient intak,es infive volunteers during a period of 14 days of weight
maintenance and 9 days of mixed diet overfeeding
Weight-Maintaining
DietOverfeeding
Free rangingEnergy, kJ
Protein, gFat , gCarbohydrate, g
Respiration chamberEnergy, kJProtein, gFat , gCarbohydrate, g
13,720f620 21,730*970
123k6 195t9
146k7 231tlO
369t17 584k26
10,940+520
98t5
17,410+880
156&B
116,t5 184,tlO
294k14 467zk24
stable with a balanced diet composed of 40% fat, 15%
protein, and 45% carbohydrate energy. They were thenstudied on two further occasions after their EI had been
increased by 60% above their maintenance energy re-
qui .rements, i.e., after 2 and 9 days of overfeeding (Fig.
1) . On the 1st day of the experiment the subjects spent24 h in a respiration chamber during which they received
a balanced diet providing 172 kJ/kg FFM and their 24-h EE was measured. This preliminary study was used,
not only to determine each individual’s “free-ranging”energy requirements, calculated as EE within the cham-
ber plus an estimated 25% for physical act ivity whileoutside the chamber (unpublished observation), but also
to accustom them
the experiment.
to the chamber and the conditions of
During the weight-maintenance period, it was neces-
sary to increase the food intake of two subjects (P.V. and
M.K.) by -400 kJ/day to maintain their body weights.
On average the subjects’ energy requirements were 13,720t 620 kJ/day while free ranging and 10,940 t 520 kJ/day while in the chamber (Table 1). During overfeeding
the subjects’ free-ranging EI was 21,730 t 970 kJ and
17,410 t 880 kJ/day while in the chamber. During theentire experi *mental period the subjects received three
meals a day composed of natural foods, which were
prepared by a trained dietitian. The breakfast was com-
posed of bread, butter and marmalade, or breakfast ce-
reals served with decaffeinated coffee or chocolate andmilk. The lunch and dinner varied from day to day and
were composed of red meats, poultry, fish, or eggs and
fresh or frozen green vegetables, pulses, white and whole
wheat bread, dairy products (cheese and yogurt), andfresh and canned fruits. Drinks consisted of fruit juiceswith or without added sucrose, tea ., and milk. Water was
allowed ad libitum. Al l . meals were taken at the Insti tute
of Physiology under supervision to ensure that al l the
food was eaten.
Body weight was measured on a Florenz torsion bal-
ance (Braunau-Wien, Austria, 200 kg t 50 g) everymorning after voiding. Urine was collected continuously
for 3 consecutive days during weight maintenance (days
-5 to -3 inclusive) and overfeeding (days 6-8 inclusive).Body composition was estimated by underwater weighing
with simultaneous underwater residual volume determi-
maintenance and overfeeding phases of the experiment
(11). During the 3 wk of the study physical activity was
monitored and recorded twice a day using a pedometerworn at the waist and an accelerometer on the nondom-
inant wrist.
Energy expenditure measurements. Measurements of24-h EE were performed in a comfortable room (5 m
long, 2.5 m wide, and 2.5 m high with a net vol of 30,6001) constructed as a large open-circuit indirect calorimeter
(13, 22). Measurements were made continuously for 22.5
h from 8:00 to 6:30 A.M. the next day. Although novigorous physical activity was permitted in the chamber,
spontaneous physical activity was estimated by radar(28). The following morning postaborptive resting met-
abol ic rate was measured for 1 h, using an open-circuit
ventilated hood, the last 30 min of which were used inthe results that we have referred to as BMR in the
remainder of the text, in spite of the conditions of
overfeeding. At the end of this period, 25 ml of blood wastaken for substrate and hormone analyses.
Analyses. The blood samples were analyzed for glucoseusing the glucose oxidase method (Beckman glucose ana-
lyzer II, Beckman, Fullerton, NY) and free fatty acidson the Dole extract. Hormone analyses included insulin
(IRI), catecholamines (norepinephrine and epinephrine)
using an high-pressure liquid chromatography technique,and thyroid hormones (T3, radioimmunoassay).
The 24-h urine collect ions were divided into day and
night samples, each of which was analyzed for nitrogenusing the Kjeldahl method and catecholamine excretion.
Data analysis. Energy intake and food composition
was determined from food tables prepared by a largeSwiss food company and by values provided by the man-
ufacturers (Nutri tive Values of food, Migros) and enteredonto a Hewlett-Packard desktop computer (HP-9830,
Hewlett-Packard, Palo Alto, CA). The metabolizable en-ergy of the n utrients was taken to be 4.0 kcal/g for
carbohydrate, 4.0 kcal /g f 0 r protei n, and 9.0 kcal/g forfat. Al l foods used in the experiment were purchased at
their outlets. Nitrogen balance was assessed during a 3-
day nitrogen intake and excretion period during both theweight-maintenance and overfeeding periods (Fig. 1). A
value of 5 mg/kg body wt per day for integumental losses
was taken into account in the total nitrogen losses (2)
In the respiration chamber oxygen consumption ., car-ation (helium dilution) on the last day of the weight
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E472 RAVUSSIN ET AL.
bon dioxide production, and spontaneous physical activ-
ity were continuously measured, and the variables wereprocessed using a Hewlett-Packard data acquisition sys-
tem (HP-3052A and HP-9825A). For data presentation
these values have been integrated over l-h periods. EEwas calculated from the overal l respiratory quotient (RQ)
and oxygen consumption (Vo2) by using the formula
EE (kcal/min)
includes not only changes in BMR and the thermic effectof food but also the increased cost of physical activity
due to a greater body weight and possible modificat ions
of activ ity. It also represents the ineff iciency of energyretention.
The data are presented as means t SE, and paired t
test analyses were used to compare the weight-mainte-
nance period with that of overfeeding.
(RQ - 0.707)
0.293 1 10.361 x voz
where 4.686 kcal/l is the energy value of 1 liter 02 at anonprotein RQ of 0.707; RQ is the measured respiratory
quotient; 0.707 is the RQ when only fat is oxidized; 0.293
is the difference between the RQ for carbohydrate andfat oxidation; 0.361 is the difference in energy value of a
liter of oxygen between an RQ of 1 and that of 0.707;
and VO W (l/min) is the rate of oxygen consumption at
STPD conditions.
Spontaneous physical activity measured by radar inthe chamber was averaged over the 24-h period andrepresents the proportion of time during which move-
ments were detected over the 24-h period (28).Overall thermogenic response to the three meals
(breakfast, lunch, and dinner) was calculated as previ-
ously described (27). In brief, the mean resting EE for
the whole day (16 h), which includes the thermic effectof the meals, was obtained by the intercept of the regres-
sion line for EE (indirect calorimetry) versus percentphysical activity (radar system). The difference betweenthis value and basal metabolic rate represents an esti-
mate of the thermic effect of the three meals; the latter
was computed for a 16-h period.Fraction of excess energy intake dissipated. One other
way to assess the overall response to overfeeding is to
express the percent of the excess EI (AEI) which isexpended over 24 h, i.e., (AEE/AEI) X 100. This value
RESULTS
Body weight and activity indexes. Figure 2 shows thatbody weight was maintained within 0.5 kg during the 14
days of the base-line period. The average weight for thelast 2 days of this weight-maintenance period was 71.32
t 3.17 kg of which 14.6 t 2.7% was fat. Overfeedingproduced an init ial rapid weight gain that became pro-gressively slower. Total weight gain after 8 days of
overfeeding was 3.21 t 0.26 kg, i.e., an increase of 4.5%
in body weight (Table 2). At this time body fat, measured
4
In-5
T
Q I
I
1~1
I
0
-- -e--v- - - - - - - - - - - - - - - - - -
w-e--
l
IA
. .-15 -10 -5 0 5 10
Days
FIG. 2. Body w t change during 14 days of wt maintenance and 9days of mixed diet overfeeding (means t SE).
TABLE 2. Body weight, 24-h energy expenditure, and basal metabolic rate in five lean subjects
SubjectsWeight
Maintenance
Z-Day
Overfeeding
g-Day
Overfeeding
Body weight, kg
MeanSEBasal metabolic rate, kJ/day
MeanSE24-h Energy expenditure, k J/day
Mean
SE
K.J.P.V.T.V.JP.G.
M.K.
K.J.P.V.T.V.JP.G.M.K.
K.J.P.V.T.V.JP.G.M.K.
65.3 66.5 69.071.1 72.7 74.968.3 69.3 71.4
83.7 84.6 85.9
68.4 69.3 71.471.3 72.5t 74.5t
3.2 3.2 2.9
7,410 7,711 8,736
7,473 8,075 8,494
7,289 7,230 7,832
9,761 9,941 9,761
7,711 7,774 8,134
7,929 8,146 8,591*
463 469 330
8,673 9,096 12,715
9,552 9,916 10,962
9,422 10,192 10,661
11,251 12,602 13,213
9,858 10,309 11,397
9,751 10,423* 11,789*
423 584 500
* Statist ically different from weight-maintenance period, P C 0.05. t Statist ically different from weight-maintenance period, P < 0.01.
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SHORT-TERM, MIXED-DIET OVERFEEDING IN MAN E473
by underwater weighing, represented 16.4 t 2.7% of bodyweight, thus indicating an increase in fat mass of 1.8 kg,
i.e., 57% of the total body weight gain. During weight
maintenance daily nitrogen intake was 19.7 t 0.9 g/day
and urinary nitrogen output was 16.3 t 1.6 g/day (3-daymeasurement). During overfeeding nitrogen intake was
31.2 t 1.4, whereas urinary output increased to 22.7 t
1.6 g/day.Figure 3 shows that activi ty, measured by pedometers
(top) or accelerometers (bottom), was not altered duringoverfeeding in the free-ranging conditions (7 days of
overfeeding vs. last 7 days of wt maintenance).
I I I
:::.j:1::::::.:::::::::
b
.‘_~.‘,‘,’:::::::: 1.:..:.:.:.: ::.:_.‘.~...‘.._ ::.:.:.:.:.:...:.:::::.:j::.:.:.:.._,~,:,:.. :. ,_,.__.
meal meal meal - s leep -
Energy expenditure. BMR was increased in all but one
subject after 2 days of overfeeding (Table 2; avg 1.7%,
NS). After 9 days of overfeeding there was a signif icantincrease in BMR from 5.52 t 0.33 to 5.94 t 0.21 kJ/min
(P < 0.05), i.e., a 7.6% increase.
o’ I 1 I I I 1 a 1 1 11
8 10 12 14 16 18 20 22 24 2 4 6
Time ( hours )
FIG. 4. Time course of oxygen consumption (VO& throughout day
and night. Dotted area represents excess Voz after 9 days of mixed-diet
overfeeding over weight-maintenance base line.
Twenty-four-hour EE was increased after 9 days of
overfeeding (Table 2) (Figs. 4 and 5). Twenty-four-hour
EE was already increased by 7% on the 2nd day ofoverfeeding (10,423 t 584 vs. 9,751 t 423 kJ/day; P <
0.05; Table 2) and by 21% on the 9th day of overfeeding
(11,789 k 500 kJ/day; P < 0.05, Table 2, Fig. 5). Thiscorresponded to an increase in diurnal (8 A.M. to bed-
time) EE averaging 7.60 t 0.37, 8.16 t 0.46, and 9.23 t
0.40 kJ/min and in sleeping EE 4.80 t 0.29, 5.10 t 0.46,and 5.53 t 0.32 kJ/min during weight maintenance and
after 2 and 9 days of overfeeding, respectively (Table 3).
-Overfeeding -
I I I I65 m 75 80 85
BODY WEIGHT (Kg)
FIG. 5. Individual changes in 24-h (A- --A) and basal (C--O) energyexpenditures (EE) expressed in kJ/min as a function of changes in
body wt caused by 9 days of overfeeding. The 2 regression lines were
calculated for preoverfeeding values of basal metabolic rate (BMR)
(dashed line) and 24-h EE (continuous line). Note that when BMR is
considered, slope of preoverfeeding values (0) are consistent with
changes induced by overfeeding, whereas it is not the case for 24-h EE
(A), i.e., EE increased more than body wt.
24 EE 24EE
T T
The relationships between body weight and the pre-
overfeeding values of BMR and 24-h EE are shown in
Fig. 5. The values of BMR after 9 days of overfeeding fitthe preoverfeeding regression line well, whereas this is
not the case for 24-h EE after overfeeding, all values
being above the regression line. The average 24-h RQwas 0.847 -t 0.010 during weight maintenance and in-
creased to 0.902 t 0.013 (P < 0.01) and 0.918 t 0.007 (P< 0.01) after 2 and 9 days of overfeeding, respectively.
Spontaneous physical activity, as measured by radar
in the chamber, was unaltered by overfeeding (7.1 t 0.9%maintenance, 7.8 t 0.6% 2nd day, and 9.8 t 1.8% 9thday of overfeeding, NS). The tendency to an increase
was accounted for by a single subject (K.J.) whose activ-
ity increased from 4.2 to 16.6%. After interview thissubject admitted that he had danced in the chamber for
2 h during the evening, elated by the termination of the
study. The estimated cost of physical activity as mea-sured by the slope of the regression line between energy
expenditure (kJ/min) and spontaneous physical activity
-8 -5 -2 2 5 a
TIME ( days 1
FIG. 3. Average pattern of activity index throughout study obtained
with pedometers (top) and accelerometers (bottom). Note low-activityvalue obtained in chamber with pedometer (24-h energy expenditure).
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E474 RAVUSSIN ET AL.
TABLE 3. Mean energy expenditures, thermic effect of food, and cost of physical activ ity
during weight maintenance and after 2 or 9 days of mixed diet overfeeding
Weight Maintenance 2-Day Overfeeding g-Day Overfeeding
Energy intake, kJ/day
Diurnal energy expenditure, kJ/min
Sleepi ng energy expenditure, kJ/min
Basal metabolic rate, kJ/min
Energy expenditure without activity, kJ / minThermic effect of food, kJ/16 h
Thermic effect of food / energy intake, %
Cost of spontaneous physical activity, kJ/min per %
10,937-r-502
7.60t0.374.80k0.295.52t0.33
6.73t0.291,176+152
10.8t1.40.026t0.003
17,451+853t8.16kO.46"5.10t0.465.65t0.33
7.20k0.441,477+159t
8.520.80.026t0.004
17,359+887t9.23kO.40"5.53t0.32"5.94t0.21"
7.8OkO.41"1,757+284t
10.2k1.60.031t0.004
Diurnal energy expenditure was measured from 8 A.M. UntiLbedtime. Energy expenditure without activity was calculated as the y-intercept of
the regression line of 64 points (15-min periods) between the amount of activity (%, x-axis) measured by radar and energy expenditure (kJ/min,
y-axis) (28). Thermic effect of food was calculated as the difference between the energy expenditure without activity and the basal metabolic
rate over 16 h (28). Cost of spontaneous physical activity was slope of the regression line between the amount of activity (%) and energy
expenditure (kJ/min) (64 points). * Statistically different from weight maintenance period, P < 0.05. t Statistically different from weight-
maintenance period, P < 0.01.
(%) tended to increase from 0.026 during weight main-tenance to 0.031 kJ/min per percent activity after 9 days
of overfeeding (Table. 3). When the effect of activity was
subtracted, i.e., the EE at 0% activity obtained by regres-sion analysis, the mean resting energy expenditure from
8 A.M. to 12 P.M. increased significantly from 6.73 t 0.29
(wt maintenance) to 7.20 t 0.44 and 7.80 t 0.41 kJ/minafter 2 and 9 days of overfeeding, i.e., increases of 6.9
and 15.8%) respectively.The thermic effect of the three meals increased signif-
icantly (P < 0.05) from 1,176 -t 152 to 1,477 t 159 and
1,757 t 284 kJ/16 h after 2 and 9 days of mixed over-feeding, respectively (Table 3). However, when expressed
as a percentage of energy intake, the total daily thermic
effect of food was unchanged (10.8 t 1.4, 8.5 t 0.8, and10.2 t 1.6%, respectively, Table 3).
Fraction of excess intake dissipated. After 9 days of
overfeeding, the mean percentage of the excess EI oxi-dized [ (AEE/AEI) x 1001 was 33 t lo%, indicating that
67% of the excess EI was stored, whereas 33% wasdissipated. The individual values were 73,22,22,26, and
24% for K.J., P.V., T.V., JP.G., and M.K., respectively.If the atypical activity of subject K.J. is excluded, the
average value for the four other subjects is -24%, whichis similar to that of K.J. when corrected for his increased
activity.
Blood and urinary parameters are presented in Table
4. Plasma glucose concentrations were unaffected byoverfeeding, whereas insulin concentrations were signif-
icantly increased (P < 0.05) already after 2 days ofoverfeeding (Table 4). Plasma free fatty acid concentra-
tions decreased significantly (P < 0.001) after 2 days of
overfeeding. Thyroid hormone concentrations and nor-epinephrine and epinephrine concentrations were unaf-
fected by 9 days of overfeeding. Similarly, urinary excre-tion rates of norepinephrine and epinephrine were un-
changed, although there was a tendency for them to
increase with 1the night.
DISCUSSION
Numereous16,29) have s
verfeeding during the day as well as during
studies of overfeeding in man (4, 12, 14-
lown that the body weight gain of overfed
TABLE 4. Effect of mixed-diet overfeeding on
postabsorptive circulating levels of substrates and
hormones and on urinary norepinephrine
and epinephrine excretion rates
WeightAfter 2 Days After 9 Days
Maintenanceof Over- of Over-feeding feeding
Plasma levels
Free fatty acids, pmol/l
Glucose, mg/dl
Insulin, pU/ml
Total Td, nmol/ l
Free T1, pmol/ l
Uptake TB, %
Total TB, nmol/l
Free TI, pmol/l
Reverse TB, nmol/lTSH, $J/ml
Norepinephrine, pg/ml
Epinephrine, pg/ml
Urinary excretion rates,
M/hNorepinephrine
Day
Night
Epinephrine
DayNight
418-t4792t28.5t0.798,t4
23.7k3.131tl
2.62AO.206.8kO.l
0.36kO.022.3k0.4
164k568&6
1.67kO.250.72t0.05
0.35kO.040.06kO.01
289&20-f
94t2
11.3k1.5'97k5
21.5zk2.030&l
2.59kO.276.7kO.2
0.31kO.022.5kO.4
152t969t7
1.71t0.200.82t0.08
0.30&0.09
0.10t0.04
2952153:94&l
11.7&2.0*100t5
21.423.13Okl
2.73zk0.226.8k0.3
0.28t0.033.OkO.6
177kll65k7
1.90k0.280.98kO. 12
0.4ot,o.o9
O.llIkO.04
TSH, thyrotropin. * Statistically different weight maintenance P
< 0.05. 7 Statistically different from weight maintenance P < 0.01.
subjects was much smaller than the minimum expected
weight gain if all the excess energy intake was stored asfat. In the classical study of Miller et al. (15) small weightgains were observed in the overfed volunteers. This study
revived Neumann’s (16) old concept of luxuskonsump-
tion, suggesting that thin people, in response to over-feeding, can induce some metabolically inefficient mech-
anism that burns off part or all of the excess ingestedenergy. In most of the cited studies it can, however, be
questioned whether physical activity increased simulta-neously with overfeeding.
In the present study body weight gain was 3.2 kg after
9 days of overfeeding with an excess energy intake of-74 MJ over maintenance requirements (Table 5). Fur-
thermore, physical ac tivity was unaltered during over-
feeding as indicated by the relatively crude techniques
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SHORT-TERM, MIXED-DIET OVERFEEDING IN MAN E475
TABLE 5. Nine-day cumulated energy balance
and energy equivalent of weight gain in five volunteersduring mixed-diet overfeeding
Energy intake for wt maintenance, MJ/9 day
Energy intake during overfeeding, MJ/9 day
Excess energy intake above maintenance,
MJ/9 day
Estimated increase in energy expenditure in
response to overfeeding, MJ/9 day*
Excess energy intake above energy expen diture,
MJ/9 day
112.4
186.9
74.4
17.8
56.6
Body wt gain, kg 3.21
Energy equivalent of wt gain, kJ/g 17.6
* From interpolatio n of the relative increase in energy expenditure
measured in the respiration chamber to free-living conditions.
using pedometers and accelerometers (Fig. 3). This
weight gain was much greater than the expected 1.9 kg
calculated if all of the excess energy intake was stored asfat, neglecting the net energy cost of lipid storage or 1.4
kg if the cost of fat deposition is assumed to be -55 kJ/g (21). By th e underwater weighing method it can be
estimated that 56% of this 3.2 kg weight gain was fatand 44% FFM. Another independent approach for deter-mining the composition of weight gain is nitrogen bal-ance. From our 3-day nitrogen balance one can calculate
that an average of -8.0 g/day nitrogen was retained inthe body if an estimate of integumental nitrogen losses
of 5 mg/kg body wt per day is taken into account in the
total nitrogen losses. If one extrapolates the 3-day bal-ance to 9 days this corresponds to a gain of -50 g of
protein/day x 9 days = 450 g of protein or -2 kg of FFM
assuming that protein represents 23% of FFM. The fat
mass gain therefore represents 38% of the weight gaincompared with 56% when estimated by underwaterweighing. It is, however, well known that nitrogen bal-
ance (as well as underwater weighing) has limitationswhen estimating the composition of smal l body weight
changes. From the results of energy balance and body
weight gain (Table 5), one can obtain a crude estimateof the composition of the gain calculated from the energy
equivalent of the tissue mass gained that averaged -18kJ/g. If one assumes that 39 kJ are stored per gram offat mass and 5 kJ/g of FFM (7), it can be calculated that
roughly 39% of weight gain was fat, whereas 61% wasFFM. In an ideal situation in which a complete energy
balance can be assessed this calculation of the energy
equivalent of weight gain may represent an adequate wayof assuming the composition of relatively small changes
in body weight. Once again in the present study, because
EE has not been measured continuously throughout theentire study, one cannot exclude systematic errors on the
calculated stored energy value.
ferent possibi1itie.s. Both BMR and 24-h EE were in-creased after 9 days of overfeeding: BMR increased by
+%, whereas body weight increased by 4.5% and FFM,
the most metabolically active tissue, by only -2.5%. Theobserved increase in BMR with overfeeding is in good
agreement with numerous studies (1, 14, 17, 19, 20, 26,30) except one (10). However, when expressed on the
basis of FFM, BMR did not change significantly withoverfeeding: 130 t 3 during weight maintenance vs. 138
t 4 kJ/kg FFM x day during overfeeding. We cantherefore conclude that the increase in BMR is mainly
related to the increase in the metabolically active tissue
mass. It is, however, impossible to exclude a residualthermogenic effect of the last meal even if the latter was
ingested 14 h before the BMR determination. Whether
the sympathetic nervous system plays a role duringoverfeeding is stil l controversial (18, 33). In the present
study neither plasma norepinephrine concentrations nor
urinary norepinephrine excretion supported the involve-ment of the sympathetic nervous system in response to
overfeeding (Table 4). In the absence of signif icant in-
creases of free or total triiodothyronine (Table 4), it isalso difficult to believe that thyroid hormones play an
important role in regulating EE during short-term over-feeding with a mixed diet. The recycling of carbohydrate
through 3-carbon compounds has been proposed as anenergy dissipative process (5), but its measurement is
not yet feasible. The small increase in postabsorptive
plasma insulin concentrations during overfeeding is ofinterest, because insulin may participate in increasing
EE (23), possibly by stimulating protein turnover rate.
The 21% increase in 24-h EE in response to overfeed-
ing was signi ficantly greater than that in BMR, i.e., 2,038vs. 662 kJ/day, respectively (Fig. 6). It represented -33%
of the excess energy intake, whereas 67% was stored.However, this value of 33% was artificially inflated by
“activity’
I
TEF
The fact that body weight gain was rather important
does not imply that EE was not increased. An increase
in overall EE can result from four different mechanisms:1) increased basal metabolic rate; 2) increased thermic
effect of food; 3) decreased work efficiency (1, 15); and
4) increased amount of physical activity or increasedbody weight-related cost of physical activity (28). n the
present study we have therefore investigated these dif-
r
97532
42 3
/
24h EE 24h EE
Weight Overfeeding
Maintenance Day 9
FIG. 6. Partition of excess 24-h energy expenditure (EE) induced
by overfeeding into 3 components: BMR, basal metabolic rate; TEF,
thermic effect o f food (3 meals); activity, increase in EE due to both
changes in activity and increased cost of physical activity.
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E476 RAVUSSIN ET AL.
one subject who considerably increased his physical ac-
tivity. When corrections were made for activity, the valueaveraged -24%, which is rather consistent from one
subject to another. It also shows that physical acti .vitycan be the most potent effector of thermogenesis and
this must be especially true in free-living conditions. The
increase in 24-h EE, which was not accounted for by theincrease in BMR, can be related to two different mech-
anisms: the increased thermic effect of food and the
higher activity-related EE. Because intake was markedlyincreased during overfeeding, 17,410 880 vs. 10,940520 kJ/day in the respiration chamber, it is logical to
expect an overall higher thermic effect of food expressedin absolute terms. The thermic effect of food over a day
(3 meals) increased from 1,176 o 1,757kJ/day in re-
sponse to overfeeding, i.e., an increase of -580 kJ/day.Thus when calculated on the basis of EI, the thermic
effect of food was unaffected by overfeeding. It is worth
noting that after 9 days of balanced-diet overfeeding, theaverage 24-h RQ was still below 1.0 (0.918 t 0.007vs.0.847 t 0.010 during overfeeding and wt maintenance,
respectively), indicati ng the absence of net “de novo”lipogenesis. In contrast, 7 days of progressive carbohy-
drate overfeeding has been shown to be accompanied by ’an increase in the mean 24-h RQ reaching an average of
1.12 n three volunteers (26). In the latter study net de
novo lipogenesis was strongly stimulated resulting in anextra cost of storing the excess carbohydrate as fat
(obligatory the rmogenesis) as well as an extra facu ltative
thermogenesis related to sympathetic nervous systemactivation as evidenced by a significant increase in uri-
nary norepinephrine excretion. From the present resul ts
we can therefore conclude that the amount of carbohy-
drate ingested was not sufficient to increase either the
obligatory or the facultat ive thermogenic components.As shown in Fig. 6 the increase in 24-h EE (2,038 kJ/
day) can be divided into three major components, eachof them accounting for approximately one-third of the
overall increase: an increase in BMR (-660 kJ/day), a
higher absolute thermic effect of food (-580 kJ/day),and a higher activity-related EE calculated by difference
(.-SO0 kJ/day).In Table 5 we have attempted to calculate a complete
g-day energy balance by interpolating our relative in-
creases in EE measured in the chamber to the free-livingconditions. It can be seen that over 9 days animals
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in
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secretarial help. They also thank the Nestle Co., Switzerland, for its
financial support.
K. J. Acheson is on secondment from NESTEC Research Depart-
ment, 180 0 Vevey, Switzerland
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