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Am J Clin N utr 1 99 4;5 9:9 55 -9 . Printed in USA. © 1994 American Society for Clinical Nutrition 95 5 Critical periods in childhood for the development of obesity1 - William H Dietz Special Article ABSTRACT Critical periods of development have been well recognized for many behavioral and developmental processes. However, as others have pointed out, such periods have not been widely reported for nutritional diseases. Many observations sug- gest that two and possibly three critical periods exist for the de- velopment of obes ty and its complications. These include ges- tation and early infancy, the period of adiposity rebound that occurs between 5 and 7 y of age, and adolescence. Obesity that begins at these periods appears to increase the risk of persistent obesity and its complications. The mechanisms that account for the increased risk associated with obesity at these ages remain unclear. Nonetheless, the existence of critical periods should serve to focus preventive efforts on these deve opmental stages. Am J Clin Nutr 1994;59:955-9. KEY WORDS Obesity, diabetes, fat distribution, develop- m ent, children Introduction Obesity is now one of the most prevalent diseases in the pop- ulation of the United States (1, 2). Although a variety of demo- graphic and behavioral factors (3, 4) appear associated with obe- sity, the familial resemblances in fatness 5, 6) indicate a signif- icant genetic effect on susceptibility to the disease. In general, the severity of obesity and age at onset affect the likelihood of the persistence of obesity into adulthood. Although childhood- onset obesity that persists into adulthood may be associated with more severe adult disease (7), childhood-onset obesity accounts for a minority of the cases of obesity present in adults (8, 9). Critical or sensitive (10) periods in development have been well described for many physiologic and behavioral (1 1) pro- cesses. For example, exposure of the fetus to rubella in the first trimester of pregnancy produces a variety of congenital abnor- malities, whereas later intrauterine exposure to the virus does not. One of the best examples of this phenomenon (12) is the effect of fetal dihydrotestosterone exposure on the external genitalia. Intrauterine exposure of females to testosterone between the 8th and 12th wk of fetal development produces female pseudoher- maphrodites. Likewise, the absence of dihydro estosterone in males during the same period produces ambiguous or feminized external genitalia (13). development entrain nutritional states, such as adult obesity, has not been carefully explored (12). Nonetheless, the identification of critical periods for the development of obesity may serve to focus preventive efforts and promote characterization of the mechanisms that entrain body fat and its distribution. In this dis- cussion, a critical period for the development of obesity will be defined as a developmental stage in which physiologic alterations inc ease the later prevalence of obesity. We will use the word entrain to describe the process that is initiated during the critical period, because its definition ‘to draw along with or after one- self” (14) does not imply a mechanism that accounts for the proces that follows. The prenatal period, the period of adiposity rebound, and ad- olescence a pear to represe t three critical periods for the de- velopment of obesity. Each of these will be considered in turn. Prenatal period Obesity Follow-up studies of infants exposed to famine prenatally or early in life and of infants of diabetic mothers strongly suggest that prenatal and perinatal over- or undernutrition influences the development of fatness in later life. In October 1944 the German occupation restricted the ood sup- plies to the western Netherlands. At the beginning ofthe occupation the average pe r capita daily ration approximated 7533 kJ (1800 kcalld) (15) and declined to 25 11 Id (600 kcal/d) in the 6 mo that followed. In May, 1945, after liberation, food supplies again pro- vided 71 14 U (1700 kcal/d). The clear delineation of the onset and end of the fami e in the Netherlands permitted a careful assessm ent of the effects of maternal nutrition on subsequent growth. At the time of their military induction, the rowth of 19-y-old Dutch men who had been exposed to famine in utero or in the perinatal period was compared with age-matched control subjects drawn from areas of Holland that had not been exposed to the famine 15). Obesity From the Division of Pediatric Gastroenterology and Nutrition, New England Medical Center, Boston, and Tufts University School of Mcd- icine, Boston. 2 Supported by grant HD25579 from NICHD and grant P30-DK46200 from NIDDK. 3 Address reprint requests to WH Dietz, New England Medical Center, Box 213, 75 0 Washington Street, Boston, MA 02111. Received May 26, 1993. Accepted for publication November 10, 1993.   b  y  g  u  e  s  t   o F  e  b r  u  a r  y 1  6  , 2  0 1 1 w w w .  a  j   c .  o r  g D  o w l   o  a  d  e  d f  r  o  

Am J Clin Nutr 1994 Dietz 955 9

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Am J Cl in N utr 1 99 4;5 9:9 55 -9 . P rin ted in USA . © 1994 Am er ican So cie ty for C lin ic al N u trit ion 95 5

C ritica l pe r iods in ch ild hood fo r the deve lopm en t

o f obes ity1 -

W illiam H D ie tz

Spec ia l A rtic le

ABSTRACT C ritical p erio ds of dev elo pm ent have b een w e ll

recog n ized fo r m any behav io ra l and deve lopm enta l p rocesses.

H ow ev er , as o thers have p o in ted ou t, such periods hav e n o t been

w ide ly repor ted fo r nu tritiona l d iseases . M any ob serva tions su g-

ges t th at tw o and possib ly th ree c ritica l p e rio ds ex is t fo r th e de-

ve lopm ent o f obes ity an d its com plica tio ns. T hese inc lude ges-

tation and early in fancy , the period of ad ipos ity rebound tha t

occurs be tw een 5 and 7 y of age , and ado lescence . O b es ity th at

beg ins a t th ese periods app ears to inc rease the risk of p ersis ten t

o besity and its com plica tions . T he m echan ism s th at accoun t fo r

the in c reased risk assoc ia ted w ith ob es ity a t th ese ages rem ain

u nc lea r. N one the less , th e ex is ten ce of c ritica l pe riod s shou ld

se rv e to focus preven tive effo rts o n th ese deve lo pm enta l

s tages . A m J C lin N u tr 1 99 4;5 9:9 55-9 .

K EY W O RD S O besity , d iabe tes , fa t d is tribu tion , deve lop -

m en t, ch ild ren

In troduc t ion

O besity is n ow on e of the m ost p rev alen t d iseases in th e pop-

u la tion of the U nited S ta tes (1 , 2 ). A lthou gh a varie ty of dem o -

graph ic and behav io ral facto rs (3 , 4 ) app ear asso c ia ted w ith obe-

s ity , the fam ilial resem blan ces in fa tn ess5 , 6 ) in d ica te a sign if-

ican t gene tic e ffec t on suscep tib ility to the d isease . In gen eral,

the severity o f ob es ity and age a t onse t a ffec t the like lihood o f

the pers is tence of obesity in to adu lthood . A lth ough ch ildhood-

onse t obes ity tha t pe rs is ts in to adu lthoo d m ay be assoc iated w ith

m ore sev ere adu lt d isease (7) , ch ild hood-onset ob esity accounts

fo r a m in ority o f th e cases o f ob esity p resen t in adu lts (8 , 9 ).

C ritica l o r sen sitiv e (10) period s in d eve lo pm ent h ave been

w ell desc ribed fo r m any phys io log ic and behav io ral (1 1) p ro -

cesses . For exam ple , exposure o f the fe tus to rube lla in th e firs t

trim este r o f p regn an cy produ ces a varie ty o f co ngen ital abno r-

m alitie s , w hereas la te r in trau te rine exposure to the v iru s does no t.

O ne of the bes t exam p les o f th is p hen om enon (12) is th e e ffec t

of fe ta l d ihydro tes toste ron e ex posu re o n the ex te rna l g en ita lia.

In trau te rine exp osu re o f fem ales to tes toste ron e be tw een the 8 th

and 12 th w k of feta l deve lopm ent p rod uces fem ale pseudoher-

m aphrod ites . L ikew ise , the absence of d ihydro tes toste ron e in

m ales during the sam e period pro duces am bigu ous or fem in ized

ex te rn al gen ita lia (1 3).

T he po ss ib ility tha t n u trition al a lte ra tions a t c ritica l p er io ds of

d eve lopm ent entrain nutr itiona l state s, such a s adult ob esity , ha s

no t been care fu lly ex p lo red (12 ). N one the less , th e iden tifica tion

of cr itica l p er io ds fo r the deve lo pm ent o f ob es ity m ay serve t

focus p reven tive effo r ts and prom ote charac te rization of the

m echan ism s tha t en tra in body fa t and its d istribu tion . In th is d is -

cuss ion , a cr itica l pe riod fo r th e deve lopm en t o f ob es ity w ill b

defined as a deve lopm enta l stage in w h ich phys io log ic a lte ra tions

inc rease th e late r p rev alence of ob es ity . W e w ill use the w orden train to descr ib e the pro cess tha t is in itia ted during the critica l

pe riod , because its de fin ition ‘ ‘to d raw alon g w ith or a fte r o ne-

se lf” (14) does no t im ply a m echan ism tha t acco un ts fo r th

p rocess tha t fo llow s .

T he prena ta l pe riod , the period of ad ip osity rebound , an d ad-

o lescen ce appear to rep resen t th ree c ritical pe riods fo r th e de

v elopm en t o f o besity . E ach of these w ill be cons idered in tu rn .

Pren ata l p eriod

Obes i ty

Follow -u p s tud ies o f in fan ts exposed to fam in e pren ata lly o

early in life and o f in fan ts o f d iabe tic m o thers stro ng ly sug gest

th at p rena ta l and perina ta l o ver- o r und ernu tritio n in fluences the

d eve lo pm ent o f fa tness in la te r life .

In O ctober 1944 th e G erm an occupat ion res tricted theood su p-

p lies to th e w estern N e ther lan ds. A t the b eg inn ing o fth e oc cup atio n

the av erag e pe r cap ita da ily ra tion app rox im ated 7533 kJ (180 0

kca l ld ) (15 ) and dec lined to 25 1 1 Id (600 kca l/d ) in th e 6 m o tha t

fo llow ed . In M ay , 194 5 , a fte r libe ra tion , foo d sup p lies aga in pro -

v ided 71 14 U (1700 k cal/d ). T he c lea r de lin ea tion of th e on se t an d

end of the fam in e in the N etherlands permit ted a care fu l assessm en t

of the effects o f m aterna l n utr ition on sub sequen t grow th . A t t

tim e of the ir m ilita ry induc tion , therowth of 19 -y -o ld D utch m en

w ho h ad been ex posed to fam in e in u te ro or in the p erin a ta l pe riod

w as com pared w ith age-m atch ed con tro l su b jec ts d raw n from areas

o f H olland th at had no t b een exp osed to the fam in e15) . Obes i ty

F rom the D iv ision o f Ped ia tric G astroen te ro lo gy an d N utritio n , N ew

England M edical C en ter, B o sto n , a nd T ufts U n ive rsi ty Schoo l of M cd

icine, B o sto n .

2 Supported b y g rant H D 25579 from N IC H D and gran t P 30 -DK 46200

from N ID D K .

3 A dd res s rep rin t req ue sts to W H D ietz , N ew England M edic al C en ter ,

B ox 213, 75 0 W ashing ton S tree t, B oston , M A 02111 .

R eceived M ay 26 , 1993 .

A ccep ted fo r pub lica tio n N ovem ber 10 , 19 93 .

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1 # { 1 4 9 }

. EJ Non-Diabetics

-. - Diabe t ics

I 9 5% Conf idence In te rva l

tJ :1AGE AT EXAM IN AT IO N (yea rs )

U .’

# {1 63 }0

0

LU

C :,

COHORT

95 6 DIETZ

w as defined as a w eigh t- fo r-he igh t > 120% of s tandard . T he prey -

a lence o f obes ity appeared low est am ong m en exposed to fam ine in

u te ro in the las t trim este r o f p regnancy o r in the imm ediate po stna ta l

per iod . In con tras t, the p reva lence of ob es ityw as inc reased am ong

young m en w ho w ere exposed to fam ine in u tero in the firs tw o

tnm es ters o f p reg nancy (F ig 1 ).

S tud ies o f in fan ts o f d iabe tic m others o ffe r add itiona l suppo rt fo r

the sugg estion tha t the th ird tr im es ter o f p regn an cy m ay rep resen t a

c ritica l pe riod fo r the en tra inm en t o f fa tness. In a la rge po pu la tio n

o f P im a m others and the ir in fan ts (16 ), m others w ere defined as

d iabe tic based on the presence of d iabe tes o r an abnorm al g lucose

to le rance tes t. P red iabe tic m o thers w ere d efin ed as those w ith nor-

m al g lu co se to le rance w ho sub sequen tly deve lop ed d iabe tes . O be-

s ity in the in fan ts and ch ild ren w as defined as a w eigh t 140% o f the

50th p ercen tile des irab le w eig h t-fo r-gesta tio na l age or 140% o f the

50th percen tile o fw eigh t-fo r-he igh t. In fan tsborn to d iabe tic m others

w ere fatte r at b irth than w ere in fan ts o f p red iab e tic o r n ond iabe tic

m others (16). F urthe rm ore , the preva lence of o besity am ong ch il-

d ren of d iabe tic m others a t ag es -9 , 10- 14 , and 15 -19 y w as

sign ifican tly h igh er than the p rev alence o f obe sity am ong child ren

of th e sam e age born to p re - o r nond iabe tic m others (F ig 2). T h e

preva lence of obes ity am ong the ch ild ren of d iabe tic m others a lso

appeared to be independ en t o f th e m other’s obes ity sta tu s at the tim e

of the ch ild ’s b irth (16).

S evera l o th er la rge stud ies have confirm ed the persis ten t ef fect

o f b irth w eigh t fo r the su bsequ en t r isk of obes ity a t ages 6 (17),

1 1 , 15 (18 ), and 17 y (19) , and in adu lthoo d (9 ). In these s tu d ies

th e track in g of b ir th w eigh t w as low er th an tha t o bse rv ed am ong

in fan ts o f d iabe tic m others. N one d ete rm ined g esta tio na l d iabe tes

o r m ate rna l obes ity , bo th of w hich af fec t b irth w eigh t and sub-

sequen t fatness. H ow ever, because the p reva len ce of d iab etes is

like ly to para llel b irth w eigh t, these find in gs a re cons isten t w ith

F IG 1 . P rev alence ofo besity in 1 9-y -o ld m en exposed to fam ine e ith er

in u te ro or du rin g early po stna ta l life . E xposure to fam ine in the las t

trim este r o f p regnancy or ea rly in fancy is asso cia ted w ith a reduced p rev-

a len ce of obesity at age 1 9 y , w hereas ex posure early in pregn an cy is

as soc iate d w ith an inc rea sed p rev alence of o bes ity at a ge 1 9 y .dap ted

from Rave lli e t a l(15 ) .

6 O

F... .‘

4 0

‘U

2 0

0

FI G 2. Prev alence o f obesity a t subsequen t ages am ong ch ild ren bo rn

to m others w ho w e re d iabet ic , p red iabet ic , o r no nd iabe tic d uring the ir

p reg nancy . A d apted from P ett it e t a l (16 ).

th e fo llow -u p stu d ies o f in fan ts o f d iabe tic m others, and su pport

the possib ility tha t the in trau te rine env ironm ent m ay en tra in sub-

sequen t fa tn ess. N one the less , none of the la tte r o bse rva tions cx-

dude the possib ility o f g ene tic de te rm inan ts th at o pera te in u te ro .

Pathophysiology

The s im p les t concep tua liza tion of the effec ts o f in u te ro nu tri-

tiona l ex posure is tha t ap pe tite reg u lation and ad ipocy te num bers

a re en tra in ed dur in g th is period . E ar ly in u te ro ex posu re to e ithe r

und er- o r overnu tr ition m ay affec t the d iffe ren tia tio n o f h ypo tha-

lam ic cen te rs respo nsib le fo r th e con tro l o f food in take15) . Late

in u tero exp osure to undern u trition m ay reduce the ex tens iv e ad i-

pocy te rep lica tion tha t o ccurs in th e las t trim es te r o f p regnancy ,

w hereas late in u tero expo sure to overn u trition m ay cause ad i-

pocy te hy perp lasia (15 ) . There fo re , ea rly u ndernu trition m ay im -

pa ir the regu la tio n of foo d in take , and p red ispo se to la te r o besity .

L ikew ise , th ird tr im es ter and postna ta l u ndernu trition or over-

nu tritio n m ay in f lu en ce ad ipose tis su e ce llu la rity and p ro tect

aga inst o r prom ote late r o be sity .

A ltho ugh these m echan ism s represen t log ica l hyp o theses, no

f irm ev idence ex is ts fo r eithe r. A dd itiona l fac to rs tha t m ay affect

ad ip ose tissue m ass inc lude d iffe ren tia l o r s ite -depen den t ad i-

po cy te sens itiv ity to o r m etabo lism of insu lin (20 ) o r g lu co co r-

tico ids (21), a lte ra tions in lipopro te in lipase or m itoch ondria l li

po gen ic enzym es (22 , 23), o r ch an ges in insu lin o r lipo ly tic hor-

m on e recep to r num bers (24 ).

T he effec ts o f p rena ta l nu tritiona l exposure on the m orb id ef-

fec ts u sua lly assoc ia ted w ith ob es ity appear d issoc ia ted from the

effec ts o f p rena ta l ex posure on fa tness , and sug gest th a t the en

tra inm en t o f obes ity and its assoc ia ted d iseases m ay be ind epen-

den t p rocesses . F or exam ple , in severa l E ng lish coh orts, low birth

w eigh t in c reased the risk of e lev ated b lood pressu re in ch ild ren

and adu lts (25 , 26), ab norm al g lucose to le rance or d iabe tes in

adu ltho od (2 7), and increased card iovascu lar m o rtality25 , 28) .

The effec ts o f low birth w eigh t on m orb id ity p ersisted afte r con-

tro l fo r geograp h ic reg ion , so cioecon om ic s ta tu s, m ode of in fan t

feed ing , and sm ok in g . T he sam e s tud ies failed to d em onstra te

any increase in m orb id ity o r m o rta lity fo r tho se ind iv idua ls

w hose b irth w eigh t w as g rea te r th an average .

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CR IT ICA L PER IO D S FOR O B ES IT Y DEV EL O PM EN T 957

T hese apparen t con trad ic tions o f f e r sev eral te s tab le hy po th e-

se s . Fo r ex am p le , in f an ts w ho se b irth w e ig h t is low because o f

f irst-trim es te r ex posure to u ndernu trition m ay incur an increased

risk o f su bsequ en t ad ipos ity and hy p erten sion or d iab e te s . C h il-

d ren w ho se b irth w e ig h t is low b ecause o f th ird -trim este r m ater-

nal undernu trition m ay in cur an in creased risk o f subseq uen t hy -

pertensio n and d iabe tes , bu t no t o besity . Perhaps the latte r m d i-

v iduals represen t th e ‘ ‘ m etab o lically obese, norm al-w e ig h t

ind iv idua l ’ ‘ (29 ). In f an ts w ho are ex po sed in u te ro to m aternal

ov ernu trition m ay hav e an increased risk o f obesity , bu t a low er

risk o f sub sequen t m orb id ity . C o n f irm atio n o f th e latter hy po th -

e s is w ou ld sug gest th at th e dev e lopm en t o f subsequen t obesity -

re lated d isease in in f an ts o f d iabe tic m o thers depends on pro -

cesse s th at d if f e r o r o ccur late r in dev e lopm en t.

Period of ad iposi t y r ebound

S ev eral sources o f data sug gest that the tim e o f ad ipo sity re -

bou nd m ay represen t ano ther critical period f o r the dev e lopm en t

o f subsequen t ad ipos ity . T he bod y m ass index [B M I; w t (k g )

d iv ided by he ig h t2 (m )] in creases in the f irst y ear o f lif e , and

sub sequen tly decreases (30 , 31 ). B eg inn ing at5 y o f age , B M I

ag ain beg in s to in crease . T he tim e at w h ich the secon d increase

occurs has been called the p erio d o f ad ipos ity reboun d (30 , 31 ).

C hanges in f atness m easured by triceps-sk in f o ld th ick ness appear

to f o llow a s im ilar patte rn (5).

L on g itu d inal observ atio ns f rom a sm all co hort in France (30 ,

31 ) and a som ew hat larg er coh ort in so u thw es te rn O h io (3 2 ) sug -

ges t that the tim e at w h ich ad ip osity rebo und b eg in s m ay hav e a

s ig n if ican t e f f ec t on f atness in ad o le scence (3 0 , 32 ) and adu lt-

hood (31 ) . In bo th ado le scen ts an d adu lts, B M I an d subscapu lar-

sk in f o ld th ick nesses w ere s ign if ican tly g reate r am ong ch ild ren

w h ose ad iposity reboun d beg an early (be f o re.5 y o f age ), co rn -

p ared w ith ch ild ren w hose ad ipo sity reb ound w as av erage (6 .0 - .

6 .5 y ) o r late (af te r 7 y ) (30 , 31 ).

A lthou gh these d ata show c learly a relationsh ip be tw een ad i-po sity rebo und and sub sequen t f atn ess , the prev alence o f obesity

has no t been ex am in ed . T here f o re , the ev idence th at th e p erio d

o f ad ip osity rebound rep resen ts a critical period f o r the dev e l-

opm en t o f subsequen t ob es ity is n o t y et e stab lish ed . A n alte rnate

ex p lanatio n f o r th e e f f ec t o f ad ipo sity rebound on ev en tual ad i-

pos ity m ay be that ch ild ren w h o reb ound earlie r g row f atte r f o r

a long er p erio d o f tim e . R ate s o f B M I increases m ay rem ain

paralle l. T here f o re , d if f e rences in f atness at subseq uen t ages m ay

on ly re f lect an earlie r onse t o f the ag e -re lated increase in f atness ,

and paralle l gain s in f atness thereaf te r. N o pu b lished s tu d ie s hav e

link ed the p erio d o f ad ipos ity reboun d to su bsequ en t m orb id ity

o r m o rtality .

Adolescence

Obesity

A do le scence represen ts the f in al p roposed period f o r th e d e-

v e lo pm en t o f obes ity . B o th the risk o f onset and pers istence o f

obesity appear greater f o r f em ale s than f o r m ales.

T he canaliz ation o f f atness w ith age app ears to in crease

th ro ugho u t ch ildho od (18 , 3 3 ). Furth erm ore , sev eral s tu d ie s ob -

serv ed an increased inc idence o f obes ity in ad o lescen t g irls (3 4 ,

35 ) . L o ng -te rm f o llow -u p s tud ie s o f ado le scen ts sugg es t that

30% of all o bese adu lt w om en w ere ob ese early in ado le scen ce ,

w h ereas on ly 10% of o bese adu lt m ale s had onse t o f th e ir obesity

as teenagers (9 ). A pp rox im ate ly 70% of obese m ales , bu t on ly

20% of o bese f em ales retu rned to norm al w e igh t ov er a 10 -

period (3 6 , 37 ). T hese f in d ings in d icate th at g irls m ay b e at par-

ticu lar risk f o r adu lt obes ity if the ir d isease is p resen t o r dev e lops

during ado lescence, and that ado le scen t-onset obes ity in f em ales

that persis ts in to adu lthoo d m ay herald a lif e lo ng pro b lem .

A d o lescence also ap pears to represen t a critical p erio d f o r the

en trainm en t o f ob es ity -assoc iated m orb id ity . In aS-y f o l l ow - u p

stud y o f ind iv idu als s tud ied during the T h ird H arv ard G row th

S tu dy (19 22 - 19 35 ), m ortality w as in creased am on g m en w ho

w ere ov erw e igh t (B M I > 7 5 th percen tile ) during the ir h ig h

sch oo l y ears w hen com pared w ith m en w ho w ere lean (B M I be

tw een 25 th and 50 th p ercen tile ) ad o lescen ts (38 ). M orb id ity f rom

sev eral d iseases w as also increased am ong b o th m en and w om en

c lassif ied as ob ese d uring h igh scho o l. T he s ign if ican t e f f ec t

h igh schoo l w eigh t o n m orb id ity and m ortality pers isted ev en

w hen w e igh t at ag e 5 3 y w as con tro lled , sugg esting that the m or-

b id ity and m o rtality e f f ec ts re su lted f rom ad o le scen t obesity d i

rec tly , rather than f rom the e f f ec ts o f ad o lescen t obes ity on adu lt

w e igh t. M en tend ed to su f f er m ore consequences o f o besity p res -

en t during ado le scence than d id w om en . D ata f rom y oun g adu lt

o v erw eigh t D u tch (39 ), D an ish (4 0 ), S w ed ish (41 ), and N orw e-

g ian m en (H T W aaler, p erson al com m un ication , 1 991 ) su pport

th es e o bse rv atio ns .

Pathophysiology

T h e m ech an ism s by w h ich ado le scen t-on se t ob es ity lead to a

in creased lik e lih ood o f adv erse seque lae or the pers is tence

obes ity is no t c lear. O n e po ten tial ex p lanatio n f o r the apparen t

en trainm en t o f m orb id ity durin g ad o le scence m ay be the p atte rn

o f f at depo sitio n that occurs at th is tim e . B oy s , an d to a le sse

ex ten t g irls , appear to depo sit f at cen trally and lo se f at periph -

e rally as they m ature (42 ) . E strog en and p roges te ro ne recep to rs

are apparen tly absen t f rom f em ale abdom inal, f em oral, o r om en -

tal ad ip ose tissue (43 ). H ow ev er, androg en recep to rs ex is t in ab

d om inal, om en tal, an d som e g lu teal depo ts (44 ). T hese f ind ing s

sugg es t that th e sex ual d im o rph ism o f ad ipo se tissue depos itio n

du rin g ado le scence m ay be de term in ed by de f au lt. I f and rogens

are p resen t, f at m ay be depos ited in traab dom inally . In the a

sen ce o f androg ens, f at m ay be depos ited in the g lu teal reg ion .

R eg ional d if f e rences in ad ipocy te recep to rs o r m e tabo lism ,

w e ll as d if f e ren tial e f f ec ts o f in su lin on g lucose up tak e and

po ly s is m ay con tribu te to th is p rocess .

In traabdom in al f at in obese adu lts p red ic ts d iabe te s (4 5 ), heart

d isease (46 ), hy pertens io n (47 , 48 ) , and hy p erlip idem ia (49 ). Fur-

th erm ore , f at d istribu tion m ay accou n t f o r a larg e p roportion

th e sex -related d if f e rences in the inc idence o f m y o card ial in f arc -

tion (50 ). Increased re lease o f f ree f atty acid s f rom in traabdom -

inal f at m ay ac t on the liv e r to p roduce hepatic in su lin re s is tance ,

and to redu ce in su lin -m ed iated suppression o f h ep atic g luco se

pro duc tio n and release (51 ). T h ese e f f ec ts con tribu te to g lu co se

in to le rance an d no n -in su lin -dependen t d iabe te s m e llitu s (52 ).

L ik ew ise , increased f ree f atty acid s in the po rtal c ircu latio n m a

decrease in su lin c learance an d con trib u te to hy perin su linem ia

(53). H yper i nsu l i n em ia and insu l i n r esi st ance have been associ -

ated w ith hy perten sion (54 ,55). T he h igh -risk p lasm a lip id pro -

f ile assoc iated w ith in creased in traabdom inal f at appears inde

p enden t o f hy perin su linem ia and abno rm al carboh y drate m etab -

o lism (56 ) . A n alte rn ativ e p erspec tiv e is th at in su lin re s istance

m ay represen t a prim ary rather than a secon dary ev en t (57 , 58

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95 8 DIETZ

Whether any o f the same potential mechanism s also predispose

to the pers istence o f obesity remains unc lear. A bdom inal adipose

tis sue appears mo re sensitiv e than does g luteal fat to lipo ly tic

stimuli (5 9 , 60 ) . Fatty ac ids released from intraabdom inal fat

ac ting on the liver may he lp ex plain w hy intraabdom inal fat co n-

tribute s to hyperinsulinem ia, and may also explain w hy obesity

rem iss ion rate s in men are higher than tho se in w omen, w ho tend

to have increased depo sition o f g luteal fat. How ever, no s tudie s

have ye t indicated that adipocy te respo nses to lipo ly tic o r lipo -

genie s timuli play a central ro le in the likelihoo d o f rem ission or

re lapse o f obes ity . Care ful s tudie s o f the ontogeny o f body fat

and its distribution and o f the sy nerg istic fac to rs that affect the

pers istence o f obes ity are essential.

Summary

These observations sugg es t that at leas t tw o and possibly three

critical periods ex is t in childho od for the deve lopment o f later

obes ity and its attendant complications o f diabe te s, hypertension.

hypercho le s tero lem ia. and cardiov ascular disease .

A ltho ugh the ef fects o f birth w e ight on subsequent obesity

have been confirmed in several s tudies , at leas t one o f w hich has

fo llow ed subjec ts into adulthood, few long itudinal o bserv ations

have fo llow ed children w ith suffic ient frequency through child-

hood and ado lescence to confirm that inc ident or pers istent obe -

sity increases at the periods o utlined above . One exceptio n is the

Third Harv ard Grow th S tudy , w hich inc luded annual measure -

ments on a sizable cohort o f children from 1 st to 12 th grades in

several tow ns near B os ton (38 ) . A ltho ugh this study did no t in-

e lude data from children < 7 y o f ag e , inc idence data in bo th

males and females appear to show an early peak that co inc ides

w ith the peak o f adipos ity rebo und, and a second peak in ado -

le scence that is more marked in fem ale s than in male s (Fig 3 ) .

These observatio ns support the likelihoo d that these tw o periods

represent critical perio ds for the onse t o f o besity . W hether these

perio ds also represent critical periods for the onse t o f persis tent

obesity is the focus o f our current research.

The mechanism s that trigg er adipose tis sue depo sition in spe -

cific locations at some periods o f fetal deve lopment and child-

hood remain unc lear. N one thele s s, these perio ds represent ma-

turational stages ideally suited for the study o f the interac tion o f

env ironmental fac to rs w ith the genes that co ntro l dev elo pment.

The mechanism s that entrain the long -term deve lopment o f the

body fat mass , the po ss ibility that the morbidity o f o besity may

depend on the critical period in w hich obes ity deve lops , and iden-

tificatio n o f the hormones and the means by w hich they induce

sex -spec ific reg ional adipo cy te replication are log ically the sub-

jec ts o f further inv es tigations.

The ex is tence o f critical periods for the deve lo pment o f adi-

pos ity and its seque lae may also serve to focus prev entive and

therapeutic e fforts on deve lopmental s tag es w hen these e fforts

are like ly to be most co st e ffec tive . For example , im proved dia-

be tic contro l may reduce the e ffects o f gestational diabe te s on

birth w e ight and subsequent fatness. How ev er, e fforts to contro l

w e ig ht during the third trimes ter because o f the putative e ffec ts

o f w e ig ht gain on subsequent fatness canno t be supported based

on the data rev iew ed. U ntil further data are forthcom ing , the po -

tential grow th re tardatio n induced by third-trimes ter w e ig ht co n-

tro l may be more hazardous than w hatever e ffec ts third-trimes ter

w e ight gain may have on neonatal adipos ity .

A ge (y ea rs )

FIG 3 . Inc idence o f o besity among 8 59 female s and 1019 males mea-

sured annually be tw een the ages o f 7 and8 y in the Third Harvard

Grow th S tudy , 1922 -193 5 . The figure suppo rts the assertion that the

periods o f adiposity rebo und (ages 5 -7 y ) and ado le scence represent

tim es o f increased risk for the deve lo pment o f obesity . Children w ere

no t s tudied be fo re age 7 y .

The re lative risks o f the complications o r pers is tence o f obesity

that orig inate at each o f the critical periods outlined abo ve remain

unclear. Likew ise , age -spec ific therapeutic success rates have no t

been established, and only lim ited data hav e been published

reg arding the po tential hazards o f w e ight-reduction therapy

children. S uch data are essential to identify the most co st

e ffec tive tim e and targe t for e ffo rts to prev ent and treat childhood

obesity. U

I gratefully acknow ledge the assistance o f Je ffrey A Flier, Richard J

Grand, and A v iva M ust for their rev iew s o f early drafts o f the manuscript,

and A v iv a M ust fo r her ass istance w ith the data inc luded in Figure 3 .

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