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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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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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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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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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p j p

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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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received an average of 74 MJ energy intake above weight

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Consequently, as reported above the energy equivalent

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In conclusion, this study shows that a short g-dayperiod of overfeeding with a nutrient-balanced diet re-

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energy balance. Although long periods of overfeeding aredifficult to study in man, the recent development of the

doubly labeled water (D2180) technique for measuring

EE may prove to be useful because it allows an integratedmeasurement over periods of weeks (25). Another pointto

in

be considered is the age of the subjects; experiments

rats show tha t adaptive thermogenesis is mainly ac-tivated in young growing animals, whereas adults have a

lower thermogenic capacity (24). t may be of interest tostudy adolescents before the end of growth to ascertain

whether their thermogenic capacity i s greater than that

of adult individuals.

The authors thank the volunteers for their participation in and

contribution to this study, Professor LeMarchand, E. Maeder, and D.

Kock for their expert technic al assistance, and J. Braissant for her

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

Received 17 December 1984; accepted in final form 24 June 1985.

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(1985 ravussin) short-term, mixed-diet overfeeding in man (no evidence for _22luxuskonsumption) (1)

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