Thermic effect of food at rest, during exercise,
and after exercise in lean and obese men of
similar body weight.
K R Segal, … , A M Nyman, F X Pi-Sunyer
J Clin Invest.
1985;76(3):1107-1112. https://doi.org/10.1172/JCI112065.
The thermic effect of food at rest, during 30 min of cycle ergometer exercise, and after
exercise was studied in eight lean (mean +/- SEM, 10 +/- 1% body fat,
hydrostatically-determined) and eight obese men (30 +/- 2% body fat). The lean and obese mean were
matched with respect to age, height, weight, and body mass index (BMI) to determine the
relationship between thermogenesis and body composition, independent of body weight. All
men were overweight, defined as a BMI between 26-34, but the obese had three times more
body fat and significantly less lean body mass than the lean men. Metabolic rate was
measured by indirect calorimetry under four conditions on separate mornings, in
randomized order, after an overnight fast: 3 h of rest in the postabsorptive state; 3 h of rest
after a 750-kcal mixed meal (14% protein, 31.5% fat, and 54.5% carbohydrate); during 30
min of cycling and for 3 h post exercise in the postabsorptive state; and during 30 min of
cycling performed 30 min after the test meal and for 3 h post exercise. The thermic effect of
food, which is the difference between postabsorptive and postprandial energy expenditure,
was significantly higher for the lean than the obese men under the rest, post exercise, and
exercise conditions: the increments in metabolic rate for the lean and […]
Research Article
Find the latest version:
Thermic Effect of Food
at
Rest, during Exercise, and after Exercise
in
Lean and Obese Men of Similar Body Weight
Karen R.Segal,BernardGutin,AsaM. Nyman, and F. Xavier Pi-Sunyer
DepartmentofMedicine, St. Luke's-Roosevelt Hospital Center,NewYork10025;College ofPhysiciansand Surgeons, Columbia
University, NewYork 10032; and the AppliedPhysiology Laboratory, Teachers College, Columbia University, NewYork 10027
Abstract
The
thermic
effect
of food at rest,during
30min ofcycle
ergome-terexercise,
and after exercise was studied ineight
lean(mean±SEM, 10±1%
bodyfat,
hydrostatically-determined)
andeight
obese men(30±2%
bodyfat).
The lean and obese mean werematched with respect to age, height,weight,
andbody massindex
(BMI) todetermine
therelationship
betweenthermogene-sis
andbodycomposition,
independent of body weight.
All men wereoverweight,defined
as a BMI between26-34,
but the obese hadthree times more body fat andsignificantly
lesslean body mass than the lean men. Metabolic rate was measured by indirect calorimetry underfour conditions
on separatemornings,
in ran-domized order,after
anovernight
fast:(a) 3
hof rest in thepostabsorptive state; (b) 3
hof
restafter
a750-kcal
mixed meal (14%protein, 31.5%
fat,
and 54.5%carbohydrate);
(c) during
30
minofcycling
andfor
3 h postexercise
in thepostabsorptive
state; and
(d)
during 30
minof cycling performed 30
minafter
the
test meal andfor3
h postexercise. The thermic effect
offood, which is
thedifference
betweenpostabsorptive
and post-prandial energyexpenditure,
wassignificantly
higherfor
the lean than the obese men under the rest, postexercise,
andexercise
conditions:
theincrements
inmetabolic
rate for the lean and obese men,respectively,
were48±7
vs.28±4
kcal over3
h rest (P <0.05);
44±7 vs. 16±5 kcal over 3 h postexercise
(P<
0.05);
and19±3
vs. 6±3 kcal over30
minof
exercise(P
<
0.05).
The thermiceffect of food
wassignificantly negatively
relatedto body
fat
content under the rest (r=-0.55),
post ex-ercise(r
=-0.66),
and exercise(r
=-0.58)
conditions. The resultsof this
studyindicate
that for menof similar
total body weight and BMI, body composition is asignificant
determinantof postprandial thermogenesis;
the responsesof
obese aresig-nificantly
blunted compared with thoseof
lean men.Introduction
The
association between
obesity andimpaired
thermogenesis,which is
adiminished
capacity forincreased
energy expenditurein
response tocertain
stimuli,
hasreceived considerable
inves-tigative
attention.
Anumber
of studies
haveshown that the risein metabolic
rateafter
ingestion
of a meal, cold exposure,nor-adrenaline
infusion,
and the
combination of
a meal plus physicalexercise,
is
significantly
smaller in obese than
lean humansAddress correspondence and
reprint
requests to Dr.Segal,Obesity Re-searchCenter,St.Luke's-RooseveltHospitalCenter, AmsterdamAve. at114thSt.,NewYork 10025.Receivedfor publication 6 February 1985 and in revisedform
6May 1985.
(1-5). However, it
has been argued thatdefective thermogenesis
would playan insignificant role in the onset orpersistence
of
human
obesity
because absoluteenergyexpenditureat restand under avariety
of conditions is significantly greater in obese than nonobesesubjects
and the difference between their ther-mogenic responses is not great enough to compensate for the generally higherenergyexpenditure of the obese(6).
Obese
people
haveagreaterbody fatcontentthan normal weight subjects but they also have a greater total body weight andleanbody
mass(LBM)' (7).
Elevated body weight wouldaccountforagreater energyexpenditure during activities such aswalking or running inwhichthe "work" done is related to
the weight which is carriedover adistance andahigher resting metabolic rate for the obese is thought to be related to their
greaterLBM since lean tissue hasagreatermetabolicratethan fat
(8-9).
Since total body weight, body fat, and LBM all increase with increasing obesity and these body composition parametersare
interrelated (9), it hasnotbeen possibletodetermine the inde-pendent relationship between body composition and thermo-genesis. It is unclear whether observed metabolic differences
be-tweenlean and obese subjectsarespecificallyafunction of dif-ferences in their fatness, since the usual lean controls for obese subjects are notmerely nonobese but also lower inLBM and total body weight. Thepurposeof this studywas toclarify the relationship between body composition and thermogenesis by comparing the responses of men ofsimilar body weight and bodymassindex (BMI) but extremely different body composi-tion.
Methods
Subjects. Eightlean and eightobese menbetween the ages of 20-32
participatedinthisstudy.Thetwogroupswerematchedwith respectto
age,height,weight,and BMI. Allsubjectswereoverweight, whichwas
definedas aBMIbetween 29-34(10-11). Theleanmen were <15%
body fat and the obesemen were >25%body fat, asdetermined by underwaterweighing (see below). Thesubjects were healthy with no
historyofmetabolicorcardiovasculardisease. An oral glucose tolerance
test(OGTT)wasadministered(seebelow) to ensure that all subjects had normalglucosedisposal.Allsubjectswereweight-stable at the time of thestudywithno morethana2kgweightlossorgain over the 6 mo
beforethestudy. Thesubjectswere instructedtoconsume a
weight-maintenance dietcontainingatleast 250 g carbohydrate/d several days beforeandthroughout the duration of theirparticipation in the study. Bodyweightwasmeasuredoneverytestdaytoconfirm weight
mainte-nance.Themen werenonsmokers andwere nottaking any medications.
Noneof themenengaged in regularaerobic exercise training but the leanmentook part in strengthtrainingorparticipated in sports such as
wrestling,football, judo,orpower-lifting.These sports areconsideredto
beprimarilyanaerobic in nature(12), although thetraining regimens
1.Abbreviations usedinthis paper:BMI,bodymass
index; BSA, body
surfacearea;LBM,leanbody mass;OGTT,oralglucosetolerance test;
RMR,restingmetabolic rate;V02max, maximum aerobic power. J.Clin. Invest.
©The AmericanSocietyforClinical Investigation,Inc.
for these sports may include an aerobic component. The written informed consentofallsubjectswasobtainedand theprotocolwasapproved by theInstitutional ReviewBoardof the St. Luke's-Roosevelt Institute for HealthSciences.
OGTT. An OGTT was performed afteran overnight (12-h) fast. After a fasting blood sample was drawn, a 75-g glucose loadin 300 ml
lemon-flavoredwater wasgiven and venous blood samples were drawn at30-min intervals for 2 h. The plasmawasseparated and analyzed for glucose andinsulin.ABeckman
glucose
analyzer (Beckman Instruments, Inc.,Fullerton,CA) was used formeasuringplasma glucose (13). Plasma insulin was measured byradioimmunoassay withcharcoal absorption with the use of a human insulin standard (14). The integrated areas under the glucose andinsulincurves werecalculated.Densitometry. Bodyfatcontent and LBM weredeterminedby
den-sitometry.Thesubjectsweretested in themorning aftera12-hfast. Body densitywasdetermined byhydrostatic weighinginastainlesssteel tank inwhich a swing seatwassuspended fromaChatillon 15-kg scale. The
subjectsweresubmergedbeneath thesurfaceof thewaterwhile expiring maximallyandremainedasmotionlessaspossibleatthepoint ofmaximal
expirationforroughly5swhile underwaterweightwasrecorded. After severalpracticetrialstofamiliarize thesubjectswith thetestprocedure, 10 trialswereperformed.Theestimatedunderwaterweightwasthehighest
valuewhich was reproduced three times (15). Residual lung volume was estimated bymeansoftheclosed-circuitoxygen dilution method ofWil-more(16),with useof a Collins9-literspirometer (Warren E. Collins, Inc., Boston, MA) and a Hewlett PackardVertekseries nitrogen analyzer (Hewlett-Packard Co., Palo Alto, CA). Twotrialswereperformed while
thesubjectsassumed asittingposition thatduplicatedbodypositionin the tankduring underwater weighing. Body densitywascalculated from theformulaofGoldman andBuskirk (17) and percentbody fatwas
derivedfrombodydensity by use of the Siri equation ( 18): percent fat
=4.95/density-4.5. LBMis thedifferencebetween totalbodyweight
and fat weight, where: fat weight = total body weight X percent
bodyfat.
Aerobicfitnesstest. Maximum aerobic power(VO2 max) was detmined by a continuous multistage exercise test on a Monark cycle er-gometer(Monark, Varberg,Sweden). Beforethe test,timewasallotted for thesubjectstobecomefamiliar withcyclingon anergometerat a constantpedalingrateandtobreathingthrough the apparatus used for metabolic measurements. The subjects began cycling atarateof 50 rpm with zero external resistance (unloaded cycling). A metronome was used
toassist thesubjectinmaintainingthe properpedalingrate.Thework
ratewasincreased in 25-W increments every 2 min until volitional
ex-haustion was reached and the subject refused to continuedespitevocal encouragementoruntil hewasunableto maintain thepedaling rate.
Duringthe secondminuteateach work rate,ventilatorymeasurements
weremade byopen-circuit respirometry with useofaBeckmanmetabolic
measurement cart(SensormedicsCorp.,Anaheim, CA), whichincludes
aturbine volume transducer,aBeckman OM-
I1
polarographicoxygen(02)analyzer, and a Beckman LB-2 nondispersive infrared carbon dioxide
(C02) analyzer (Beckman Instruments, Inc.). The subjects breathed
througha Hans-Rudolfnonrebreathingvalve and useda
mouthpiece
andnoseclips.The gasanalyzerswerecalibratedbeforeandafter each aerobic fitnesstestwith 100% nitrogen,room air, andagas mixture
containing4%CO2and 16%02.Foreach measurement, the fractional concentrationsof02andCO2 (FEO2andFECO2),oxygenconsumption
(VO2), carbon dioxide production(VCO2),minute ventilation (VE), and theventilatoryequivalent for
02
(VE/VO2) wereobtained.Submaximumaerobic fitnesswasdetermined byestimationof the ventilatory threshold from the test data. The ventilatory threshold is the
highestworkrate or
V02
beforeVEincreasesoutof proportiontoV02 (19), owingto stimulation ofventilation bynonmetabolically producedCO2which derives from thebufferingoflactic acid (19). The fitness test datawere used toprovide descriptive information about the aerobic fitness level of thesubjectsandtodetermine the appropriate work rate for eachsubject duringthethermogenesistestswhichinvolved exercise.
Thermogenesis
tests.Thesubjects
refrained fromstrenuousactivity
onthe
day
before each trial.They reported
tothelaboratory
at9:00a.m.in thepostabsorptivestateafter a 12-hfastonfournonconsecutivedays; thedayswere nonconsecutivetoavoid any carryovereffectsbetween treatments.On eachday,after a30-min rest period, base-line
postab-sorptive metabolicrate wasmeasured. Three5-min measurements were made within a 30-minperiod(at5-10,
15-20,
and25-30min) in order toavoid discomfort fromcontinuous useofthe mouthpiece. The three measures wereaveragedand thecoefficient ofvariation across the three measurements was <2%. The laboratory was maintained at 240Cthroughoutthestudy.The gasanalyzerswere recalibrated (seeabove)
every half-hour to correctfor driftin theanalyzers.
The order ofthefollowingfourexperimentaltreatments was ran-domizedindependently foreachman:
(a)Postabsorptive restingmetabolic rate(RMR)wasmeasuredfor thelast 6 min of every half-hour for 3 h while thesubjectssatquietly. Theywereallowedtoreadorlisten tomusicthroughout the measurement
period.
(b) PostprandialRMR was measuredforthe last 6 minof every half-hourfor 3 h after the subjects consumed a 750-kcal liquid mixed meal (Ensure; Ross Laboratories, Columbus, OH) which was 14% protein, 31.5%fat,and54.5% carbohydrate. The test meal was consumed within 5 min.
(c)Postabsorptivemetabolic rateduringandafterexercise was mea-sured. After thebase-lineRMR measurement, thesubjects exercised for
30 minon aMonarkcycleergometer at the work ratejustbelow each
individual's ventilatorythreshold. Metabolic rate during exercise was measuredfrom5to10,15 to20,and25to30 minofthe exercise period.
Postexercise metabolicratewasmeasuredduringthefourthto tenth min post exercise and for the last 6 min of every half-hour for 3 hafterexercise.
(d) Postprandialmetabolicrateduringandafterexercisewas mea-sured
following
theprocedures described above in(c)except that thesubjects
consumed the 750-kcaltestmeal at30 minbeforethe startofexercise.
Theexerciseintensitywasadjusted accordingtoeachsubject'slevel
of aerobicfitnessbecause,
owing
todifferences among thesubjectsin their level of aerobicfitness,
agiven constantworkintensitymay beextremely strenuous or too mild.This would result in differencesin substrate
utilization,
blood lactateaccumulation,
and core temperature, and couldinfluencetheexercise- andpostexercise-thermogenicresponses. The workrate wasassignedonthebasis ofeachsubject's ventilatory threshold,whichreflectsthehighest
workratebeforetheonsetofanaero-biosis,
insteadofapercentageofthemaximum,
because theformerisperhapsa morereliablemeasuresince itisaphysiological parameter while the latterdependsonthemotivation of thesubjectandhis
will-ingnessandabilitytoexercisetoexhaustion.Furthermore, Simonetal.
(20)found that allsubjectswereabletocomplete>30 min ofcontinuous exerciseatthe workrate
just
below theventilatory
threshold.Variation among thesubjectsin the absolute workintensityshould
nothaveaffected the thermic effect of foodduringexerciseadversely;in
a
previous
study (5),we compared thethermiceffect of foodduring
exerciseat a constantwork
intensity
forallsubjects
andawork rateassigned
onthe basis of eachindividual'sventilatory
threshold and ob-tained very similar results.Foreachmetabolic measurement, the respiratory quotient(VCO2/
V02)
wascalculated andthe result was converted to kilocalories by use oftheWeirequation (21):kcal= [(1.1X RQ)+3.9]X
V02
Analysis
of
data.Comparisonof the thermic effect of foodat restand post exercise in thetwogroupswasmadebyapplyinga2X2X2
X 6four-way analysisof variance withrepeatedmeasures(22)tothe
RMRfrom 0to 180 minonthe4dusinggroup(leanorobese),food
(mealor nomealtrials),exercise(restorpostexercise),andtimeasthe factors. Metabolicrate wasexpressedbothasoxygen
consumption
andascaloric
expenditure.
Comparison
ofthethermiceffect of foodduring
exercise in thetwogroupswasmadebyapplyinga2X2 two-wayanalysisof variance with
repeatedmeasures totheexercise metabolicratedata from thefasting
andfed exercise trialsusinggroup(asabove)and food(mealor nomeal)
as thefactors.
Comparison of the thermic effect of foodatrestwith thethermic effect of foodduringexerciseacrossthetwogroupswasmadeby
appli-cation of a 2X2X2 three-wayanalysisof variance withrepeated mea-sures tothe metabolicratedata obtainedduringthetwo30-min exercise
sessionsandduringtheequivalent 30-min
periods
onthetworestingdays. Thefactorsinthisanalysisweregroup,food,and exercise(restor
exercise)withrepeatedmeasures onthe secondtwofactors.
Foreachofthe above analyses,significantFratiosfromtheanalyses
of variancewerefollowed by post hoccomparisons usingtheappropriate
error termsfromtheanalyses ofvariance(22).
Ananalysis ofvariance with repeatedmeasures wasappliedtothe
base-lineRMRvaluesobtainedonthe 4 d inordertodeterminewhether therewassignificant day-to-day variationin
fasting
RMR. Thereliability
ofrepeated base-line RMRmeasurements wastestedbythe intraclass
correlationmethod(22).
Comparisons ofmaximal andsubmaximal aerobic
fitness,
LBM,RMR(expressed in absoluteform,and relativetobodyweightandLBM),
andthe resultsofthe OGTT in thetwogroupsweremadebyapplication
of one-wayanalysesof variancetoeachof these variables.
The absoluteincrementsin energyexpenditureduetoingestion of thetestmealwerecalculatedfor thesedentary, exercise,and post exercise trials bysubtractingthefastingvalues from thefedvaluesfor
appropriate
timeperiods: 0-180 min for the
resting
trials with and without thetestmeal, the 30 minofexerciseonthetwoexercise trialsforthethermic effect of foodduring exercise,and0-180 minutes postexerciseafter the
twoexercise trials(withand without
food)
forthe post exercisethermic effect of food.Correlations between these fed minusfasting
differencescores,whichrepresent the thermiceffectof foodatrest,
during exercise,
and postexercise, respectively,and variables suchasLBM,percentbody fat,submaximal and maximal aerobic
fitness,
andareaunder theglucoseandinsulincurvesfromtheOGTTwerecalculated in ordertoexamine
therelationshipsamong
thermogenesis,
bodycomposition,
aerobicfitness,
and insulin andglucoseresponsesto anoralglucose challenge. Stepwise multivariate regression analyses were
applied using
thethermic effect of foodatrest,
during exercise,
and postexerciseasthedependentvariablestostudythe
independent
effects of bodycomposition,
glucose tolerance, and levelofphysical fitnessonthermogenesis.
For allstatisticalanalyses the 0.05 levelofsignificancewasused.
Results
The
subjects'
characteristics
areshown inTable
I.The
twogroups weresimilar with
respect to age,height, weight, BMI, and body
surface
area(BSA).
Therewasalmostathreefold differencebe-tweenthe groups in
their
body
fat
content, and LBMwas morethan 20%
lowerfor the
obese than the leanmen.V02
max wassignificantly
lower
for the obese
menwhenexpressed in absolute
form
(milliliters
perminute)
and
relative
tototal
body
weight.
Relative
toLBM,V02
max was notsignificantly
different for thetwogroups. The
V02
maxvalueswerewithin
the range observedin healthy but
nothighly aerobically trained
menof similar
age(12).
Theventilatory threshold occurred
at asignificantly
lower power output for the obese than the lean men but at a similar percentage ofV02
maxfor
thetwogroups (TableI).
Thetwogroups didnot
differ reliably
with respect tofasting
plasma glucose
orthe area under the glucose curve butfasting
plasma insulin
and the area under the insulin curve weresig-nificantly
lowerfor
the lean than the obese men (TableI).
The
fasting, base-line
measurementof
RMR didnot varysignificantly
acrossthefour
treatmentdaysfor either
group. Thecoefficient of
variation in RMR across the4 dwas 2.9%. The intraclass correlation coefficient was r =0.99, indicating
thatTable I. SubjectCharacteristics*
Obese(n=8) Lean(n=8) P
Age 25.4± 1.6 24.6± 1.2 NS Weight
(kg)
96.4±4.3 95.0±4.3 NS Height (cm) 179±2 180±3 NSBMI(kg/m2) 30.0±.9 29.6±.6 NS
BSA(m2) 2.15±.06 2.15±.06 NS Percentfat 30±2 10±1 <0.001
LBM(kg) 67.4±2.7 85.0±3.2 <0.001
Maximumaerobicpower
Power output (W) 194±10 231±33 <0.05
V02
(mil/min)
2746±127 3341±85 <0.05(ml/kg/min) 28.9±1.9 35.5±1.1 <0.05
(ml/kgLBM/min) 41.2±2.4 39.5±1.1 NS Ventilatory threshold
Power output (W) 75±7 106±9 <0.05
V02
(ml/min)
1427±87 1642±86 <0.05 PercentV02max 52.2±2.8 49.4±2.9 NS Resting metabolic rate(kcal/min) 1.305±.052 1.479±.061 <0.05V02
(ml/min)
268±10 308±13 <0.05(ml/kg/min) 2.80±.13 3.28±.15 <0.05
(ml/m2BSA/min) 125±4 144±6 <0.05
(ml/kgLBM/min) 4.01±.19 3.65±.17 NS Fasting insulin
(AU/ml)
22±4 13±2 <0.05 Fasting glucose(mg/dl) 82±2 83±2 NS Insulin area(MU/mi)t
512±119 216±33 <0.05 Glucosearea(mg/dl)t
449±28 403±19 NS*Values expressed as
mean±SEM.
$Integrated over 2 hfollowinga75 g oralglucose load.
the
measurementof
RMR wasextremely
reliable. Base-line RMR,averaged
overthe
four
treatmentdays,
wassignificantly
lowerfor the obese than
the leanmenwhen
expressed
in absolute
form
(kilocalories
perminute
orV02
milliliters
perminute)
andrelative
to totalbody
weight
and
BSA. Relative
toLBM,
RMR was notsignificantly different for the
twogroups.The
analyses of variance
yielded identical
results whencaloric
expenditure
and
oxygenconsumption
wereusedasthe
depen-dentvariables.
Postabsorptive
and
postprandial V02
under
theresting and
postexercise conditions
areshown in
Figs.
1and 2.
The
four-way
analysis
ofvariance which used
group,food (meal
or no
meal), level of exercise (rest
orpostexercise),
and
time
(the
half-hourly
measurements)
asthe
factors
yielded
asignificant
food
Xgroupinteraction,
indicating
that
the thermic effect of
food
wassignificantly higher
for
the lean than the obese men. Theexercise
Xfood
Xtime interaction
wassignificant which
reflects
thedifferent time
courseof
thethermic effect of food
under the
resting
compared with
the postexercise condition.
As shown inFig. 2,
underthe postexercise
condition,
thethermic
effect of food
does notmanifest
as anincrease in metabolic rate, but rather asareduction
in therateof
decline inmetabolic
rateafter exercise.
Theexercise
Xfood
Xgroupinteraction
wasnotsignificant
whichindicates
that thedifference
between thethermic
effect of
food in the two groupswasroughly
the same under theresting
and postexercise conditions.
In otherwords,
2,200
-r T
i
Meal
Mea
T
i
2,100
-2,000
-\ Leon,
i postprondial
Leor,
-- postacnsorptive
Obese,
postprandial
Obese, postabsorptive
Baseline 30 60 90 120 150 180
TIME (minutes)
Figure 1.Resting metabolicrates of lean and obese men over 3 h in thepostabsorptivestateandaftera750-kcalmixedmeal. The shaded areasrepresent thethermic effect of foodfor each group.
exercise
and restconditions for either
group.Expressed
asthe
increment
incaloric
expenditure
over3
h, the
thermic
effect of
food
at rest was48±7 and 28±4
kcal,(mean±SEM)
(P
<0.05)
for the lean and obese
men,respectively,
and
over3-h
postex-ercise,
44±7and 16±4 kcal
for the lean
andobese
men(P
<
0.05),
respectively.
The
difference between the
energyexpended
during exercise
under
the
postprandial
and
postabsorptive conditions is
shown
in
Fig.
3. The
thermic
effect
of
food
during
exercise
wassignif-icantly
greaterfor
the lean than the obese
men;during
the
30-min
exercise bout, the
difference
in
energyexpenditure
between
the
postprandial
and
postabsorptive
treatments was19±3
vs.6±3 kcal
for
the lean and obese
men(P
<0.05).
The
thermic
effect of food
was greaterfor the lean but
notfor the obese
menduring
the
30-min exercise bout than
during
the
equivalent
30-min
period of
rest.2
Jxercis
260
-TiT--l^. T
Lean,
T ~~~--.4
Leon,
Tpostabsorptive
Obese,
postprondial
Obese, ae 1 1 postabsorptive
c
E
._
0
1,900
-1,800
-1700
1.600
-1,500
-T ,I Lean,
postprandial
Lean
postabsorptive
Obese,
postprandial
; - Obese, postabsorptive
1
0 10 20 30
TIME (minutes)
Figure 3. Metabolic rates of lean and obese men during 30minof cy-cle ergometerexercise performedin the postabsorptive state and 30 minafterthe startof a 750-kcal mixed meal. The shaded areas repre-sentthethermiceffectoffoodduring exercise for each group.
The peak increase in
postprandial metabolic
rateduring
theresting
treatmentoccurred
significantly later for the obese
com-pared
withthe lean men(95.6±9.4
vs.61.9±5.3 min
after the
meal).
The time at whichthe peak increase
inpostprandial
met-abolic
rateoccurred
waspositively
related
tobody fat
content(r
=0.56) and
negatively
related
tothe
thermic
effect
of food
during
exercise(r
=-0.48).
Since theexercise bout
was per-formed from 30 to 60min
after the start of the testmeal, it
ispossible
that the threefold lowerthermic
responseduring exercise
for the obese
compared
with thelean men isrelated
to theirdelayed
response to the meal.Percent
fat
wasthe best
predictor (among body composition
parameters, which included
percentfat,
LBM, body
weight,
BSA,
and BMI;
theOGTT results; and aerobic fitness parameters) of
the thermic effect offood at rest
(r
=-0.55),
postexercise (r
=
-0.66),
andduring
exercise(r
=-0.58).
The
correlation
be-tween
aerobic
fitness(VO2 max) and the thermic effect of food
was not
statistically significant under either the
resting
(r
=0.41)
orpost
exercise (r
=0.37)
conditions.
Butaerobic fitness and
body
composition
aresomewhatconfounded because the
lean men weregenerally
morefit than the obese
men.When
body
fat
waspartialled
outstatistically,
the
correlation
between
aerobic
fitness
and thethermic effect of food
wasreduced
toalmost
zero(r
=0.04).
Fasting
plasma insulin
andthe
areaunder the
2-hinsulin
response curvefollowing
75-g
oralglucose
appeared
tobe
relatednegatively
tothe thermic effect offood;
however,
body
fat contentwas
roughly colinear with both
fasting
insulin
level (r=0.74)
andinsulin
area(r
=0.84),
andafter
body
fat
wastaken
into
account,these variables
were notsignificantly
related tothermogenesis.
Discussion
10 30 60 90 120 150 180
TIME AFTER EXERCISE
(min)
Figure2.Postexercise metabolicratesof lean and obesemenin the
postabsorptiveandpostprandialstate.The mealwasgiven30min be-fore thestartof the30-minexercise bout. The shadedareasrepresent
thepostexercise thermic effect of foodfor eachgroup.
It hasbeen arguedthat defectivethermogenesiscouldplay only
asmall role in theonsetandpersistenceof humanobesity
be-cause, despite thesignificantly smallerthermogenic responses toavariety of stimuli which have beennotedbyanumber of
investigators, absoluteenergy expenditure isgreater for obese
compared with lean individuals under differentconditions(6, 9). Thereasonfor this is that inpreviousstudies obesesubjects
1110 Segal, Gutin, Nyman,andPi-Sunyer
a
E
1.> 380
-360
-340
-320
300
-280
-26C
420-400
-380
-360
-340
-320
-300
cE
0
280
-400.7
were
compared
with nonobese controls
whousually
have notonly less body fat but less LBM and lower total body
weight
and
BSA.
In the present study we made use
of
a newmodel;instead
of using
anonobese, nonoverweight control
group, wecompared
the obese
groupwith
menwho
wereoverweight, according
totheir BMI, and matched
tothe obese
menwith
respect toage,height,
weight, and
BMI. The two groupsdiffered in their body
composition such that
one group wasextremely lean with
anelevated
LBMaccounting
for their
excessweight
and the other
was obese
with
bodyfat accounting for their
excessweight.
The
primary
finding of this study
wasthat
thethermic
effect
of
a750-kcal mixed
liquid
meal
wassignificantly
smaller for the
obese
than the lean
men at rest andduring
andafter
submaximal
cycle
ergometerexercise. And,
contrary tothe
findings of
other
studies (6,
9), absolute
energyexpenditure
was notgreaterfor
the obese than the lean
menunder
anyof the
testconditions
(Figs.
1-3).Thus, when the effect of
excessweight
per seis
con-trolled for
by
useof
alean
control
groupthat
is similar in
degree
of
overweight
tothe obese
group,obesity
is associated with
re-duced
energyexpenditure
and
adiminished
capacity
for
ther-mogenesis.
Recent
studies have suggested that blunted
thermogenesis
is
related
toimpaired
glucose
tolerance(23),
afrequent
compli-cation of
obesity,
rather thanobesity
per se. Inthe
presentstudy,
all
subjects had
normalglucose tolerance,
according
tothe
criteria
of the National Diabetes Control
Group (24). However,
the obesesubjects
werehyperinsulinemic
compared with the lean
meneven
though
fasting
glucose
andthe 2-h
glucose
responsetoa75-g glucose
load
weresimilar
for the
twogroups.Both
fasting
insulin and the
areaunder the
2-hinsulin
curve werestrongly
related
tobody fat
content.The
larger insulin
responsefor the
obese
subjects,
suggestive
of
adegree
of insulin
resistance, is
consistent with other studies
(25, 26).
This
insulin resistance of
the obese
compared with the
leansubjects
maybe related
totheir blunted
thermogenic
responsessince
animportant
role
for
insulin in thermogenesis
hasbeen suggested
(27).
Arecentstudy
demonstrated
that
insulin infusion increased
thethermic
effect
of exercise in
ratskeletal muscle
(28).
Theresults of the
presentstudy
are notincompatible
with the idea that
insulin plays
arole in
thermogenesis: Ravussin
et al.(29) found
adecreased
thermic
response toinfused glucose and insulin in
insulin-re-sistant obese
subjects.
It
is
possible
that the blunted
thermic
responses are
related
tothe
sensitivity
tothe level
of insulin
rather
thanthe absolute
quantity of insulin
present.The
thermic
effect of food
wassimilar
underthe resting and postexercise conditions.
However, thetime
courseofthe thermic
effect
of food differed between the
twoconditions:
underthe
post
exercise
condition,
arise
inmetabolic
rateduring
thepost-prandial
treatment wasmasked
by the postexercise decline inmetabolic
rate.Regardless,
for
both the lean and obese groups postexercise,
RMR wassignificantly
greaterin
thepostprandial
than the
postabsorptive
stateeventhough thisthermic effect offood
was notgreater post exercise than at rest.There was a
significant
thermiceffect of food
duringexercisefor
both groups asindicated
by the greater energyexpenditure
during
the 30-minexercise
bout in the postprandial than thepostabsorptive
state. Forthe lean but not the obese men, thethermic effect of food during
exercise was greater than the thermic effect offood
at restduring the equivalent30-min
period of thetwo resttrials
(RMR
from 30to60min).
This
isconsistent
with the results
of
otherstudies
(5, 30, 31),
although
somein-vestigators have
notfound
alarger
thermic
effect of food
during
exercise than
at rest evenin normal
weight subjects (32, 33).
Differences
amongthese
studies
in meal size and
composition,
andthetiming of
the meal andexercise
mayaccountfor
theseconflicting findings.
The
threefold lower thermic
responseduring
exercise for the
obese
compared
with the
leanmenmaybe related
tothe
delayed
responseof the
obese men tothe meal
since the exercise bout
was
performed from 30
to60
minafter the
startof the
testmeal
and the
peak increase in
postprandial
metabolic
rateoccurred
95.6 min after the meal for the
obese groupcompared
with 61.9
min
for the
lean group.Although
thepeak thermic
responsetofood occurred later for
the obesethan the lean
men,there is
noevidence that the
responseis
moreprolonged
in the
obesesubjects
which
would
yield
underestimations
of the
thermic effect of food
over
the 3-h
resting
and postexercise
periods.
Infact,
asshown
in
Figs.
1 and2,
atthe end of
thethird hour of
measurement,the
elevation in metabolic
rateabove
the
fasting,
base-line level
wasgreater,
though
notstatistically
different,
for the lean than
the obese
subjects
under
both the
resting
and
post-exercise
con-ditions.
Recent
studies
haveshown that the thermic effect
of
food is
larger
(34) and smaller
(35)
in
highly aerobically
trained
com-pared with untrained individuals.
Inthe
presentstudy,
the
thermic effect of food
wasnotsignificantly
correlated with level
of aerobic fitness (VO2
max). However,
eventhough
V02
maxwas
significantly
greaterfor
thelean than the
obese men, theaerobic fitness levels of
the leanmenwereconsistent with values
obtained in untrained
menand athletes who
participate
in
sports thatrely
onmuscle
strength
orspeed
morethanon ahigh
aerobic
capacity.
It
has been
suggested
that differences between thermic
re-sponses
of lean and obese
persons maybe related
toreduced
sensitivity
in the obese
tothe
actions of
thermogenic
hormones
stimulated
by
the
ingestion
of
ameal
orthe
confluence of food
plus exercise
or to areduced
thermogenic capacity
in brownadipose
tissue
(3, 5,
36, 37).
Another
mechanism
which
might
contribute
tothelower
thermic
responsesof the
obesecompared
with the lean
menin the
presentstudy is
thermogenesis
in skeletal
muscle. It
is
likely
that thefar
greater LBMfor the lean
groupaccounts
for their
greater RMR becauseof the
greater energyexpenditure
of muscle
compared
with fat tissue. Protein
turnovermay account,
in
part,for the elevated
energyexpenditure (38),
which in the
presentstudy,
maybe associated with increased
LBM
for
the lean men.Protein
synthesis
is
anenergetically
ex-pensive
process(39), accounting
for 10-15% of
basalmetabolic
rate
(37).
Therefore,
evenif
the rateof
protein
turnoverweresimilar for the
obeseand lean
groups,absolute
protein
breakdown
and
synthesis
would be greaterfor
theoverweight
but lean mencompared
with
theobese
men,owing
tothe
far
greatermuscle
mass
of
theformer
group.It
has been
proposed
that skeletal
muscle may be onesite
for
nonshivering thermogenesis
(36, 37). Thus,
it ispossible
that thelarger thermic
responsesof
the leanmenmight
beattributed
in part to
their
greater skeletal muscle mass.However, further
quantitative
study of
thecapacity
for
thermogenesis
within
muscletissue
is
neededbefore definitive
statementsof
the roleof
LBMinthermogenesis
canbe made.In
conclusion,
this study
showed thatRMRand thethermic
effect
of food atrest,during exercise,
and post exercise aresig-nificantly
greater for lean than obese men of similarheight,
a significant determinant of thermogenesis; the capacity for
thermogenesis
is blunted in overly fat compared withoverly
muscular men.
Acknowledgments
This study was supported in part bya Biomedical Research Support grantfromTeachers College, Columbia University and by theNational
InstitutesofHealth grant AM26687.
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