2020-04-01 Reader\'s Digest AUNZ

UsFat, believesthismaybethebody’s

wayofvigorouslydefendinga certain

weightrange,calledthesetpoint.

Onceyougainweightandkeepthe

weightonforaperiodoftime,the

bodycangetusedtoitsnew,larger

size.Whenthatweightdrops,a bunch

ofsubtlechangeskickin– tothehor-

monelevels,thebrain– slowingthe

restingmetabolismandhavingthe

effectofincreasinghungerandde-

creasingsatietyfromfood,allina

seemingconspiracytogetthebody

backuptothatsetpointofweight.

“Idon’tthinkmostpeopleappreci-

atehowbigthesemetabolicchanges

canbewhentheylosea lotofweight,”

Aamodtsays.“Weightgainandloss

arenotsymmetrical:thebodyfights

muchmorestronglytokeepweight

fromdroppingthanitdoes to keep

weightfromincreasing.”

7

RESEARCHERSDON’T

FULLYUNDERSTAND

WHYTHISMETABOLIC

SLOWDOWNHAPPENS

Therearesomeinterestinghypothe-

ses,however.Oneofthemostpersis-

tentisanevolutionaryexplanation.

“Overhundredsofmillennia,we

evolvedinanenvironmentwhere

wehadtoconfrontfrequentperiods

ofundernutrition,”ProfessorRosen-

baumsays.“Soyouwouldpredict

thathumanDNAwouldbefullof

genesthatfavourthestorageofextra

kilojoulesasfat.Thatabilitywould

to some extent increase our ability

resultofyourhighermetabolism.”

DrJensenalsonotesthatit’sdifficult

forpeopletosustaintheworkoutsre-

quiredtokeepthemusclemassthey

gained.“Formost,it’skindofimprac-

tical,”headds.

Overall,hesays,“There’snotany

partoftherestingmetabolismthatyou

havea hugeamountofcontrol over.”

6

DIETINGCAN

SLOWDOWNYOUR

METABOLISM

Whileit’sextremelyhardtospeedup

themetabolicrate,researchershave

foundtherearethingsthatcanslow

it down– likedrasticweight-loss.

“[Crashdiets]probablyhavethe

biggesteffectonrestingmetabolism,”

saysDrJensen.Butnotina goodway.

Foryears,researchershavebeen

documentinga phenomenoncalled

‘metabolicadaptation’.Aspeople

loseweight,theirbasalmetabolic

rateactuallyslowsdowntoa great-

erdegreethanwouldbeexpected

fromtheweightloss.Tobeclear,it

makessensethatlosingweightwill

slowdownmetabolism.Slimming

downgenerallyinvolves muscle

loss,which,inturn,meansthebody

doesn’thavetoworkashardtokeep

running.Buttheslowdown after

weightloss,researchershavefound,

oftenappearstobesubstantially

greaterthanmakessensefora per-

son’snewweight.

Neuroscientist SandraAamodt,

authorofthebookWhy Diets Make

70 April 2020

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