partofyourtotalenergyexpenditure–
abouttento 30 percent(unlessyou’re
a professionalathleteorhavea highly
physicallydemandingjob).Digesting
foodaccountsforabouttenpercent.
“It’sgenerallyacceptedthatformost
people,thebasalmetabolicrateac-
countsfor 60 to 80 percentoftotalen-
ergyexpenditure,”saysneuroscientist
andobesityresearcherAlexxaiKravitz.
“Thisiswhyit’snotsosurprising
thatexerciseleadsto[statistically]
significant,butsmall,changesin
weight,”Kravitzadds.“It’snotnoth-
ing,butit’s not nearly equal to food
i nt a ke.”3
METABOLISMCAN
VARYALOTBETWEEN
PEOPLE,AND
RESEARCHERSDON’T
UNDERSTANDWHY
It’struethattwopeoplewiththe
samesizeandbodycomposition
canhavedifferentmetabolicrates.
Onecanconsumea hugemealand
gainnoweight,whiletheotherhas
tocountkilojoules.
Butwhythisisremainsa‘black
box’,saysprofessorofphysiolog y
WillWong.“Wedon’tunderstand
themechanismthatcontrolsa per-
son’smetabolicrate.”
Researchershavebeenabletofind
somepredictorsofhowfastaper-
son’smetabolismwillbe.Thesein-
clude:theamountofleanmuscleand
fattissueinthebody,ageandgenet-
ics (though researchers don’t knowREADER’SDIGEST1
YOURMETABOLISM
ISINEVERYCELLIN
YOURBODY
A lotofpeopletalkabouttheirmetab-
olismasif it’sa muscleororganthey
cansomehowcontrol.Butinreality,
thetermreferstoa seriesofchemical
processesineachcellthatturnthe
kilojoulesyoueatintofueltokeep
youalive.“It’stheculminationof
differenttissueswithdifferentneeds
andhowmanykilojoulesittakesto
keepthemfunctioning,”saysDrMi-
chaelD.Jensen,a physician-scientist
whostudiesobesityandmetabolism.
Thebody’smajororgans– thebrain,
liver,kidneysandheart– account
foroverhalfoftheenerg yburnedat
rest,whilefat,thedigestivesystem
andespeciallythebody’smuscles
accountfortheremainder.2
MOSTOFTHE
ENERGYYOUBURN
ISFROMYOUR
RESTINGMETABOLISM
Therearethreemainwaysyouburn
energy:a)thebasal metabolism,
whichistheenergyusedforyour
body’sbasicfunctioningwhileatrest;
b)theenergyusedtobreakdown
food,also knownasthe thermic
effectoffood;andc)theenergyused
inphysicalactivity.Oneveryunder-
appreciatedfactaboutthebodyisthat
yourrestingmetabolismaccountsfor
a hugeamountofthetotalkilojoules
youburneachday.Physicalactivity,
ontheotherhand, accounts for a tiny68 April 2020