The growing epidemic of childhood obesity worldwide promises both short- and
long-term adverse consequences. Pediatric clinicians have already noted an
alarming increase in type 2 diabetes in adolescents, for which obesity is the
chief cause.1 Increasing obesity,
type 2 diabetes, and associated risk factors may be reversing previously
declining rates of ischemic cardiovascular disease in western societies and
presaging a new endemic in the developing world.
Fundamentally obesity arises from an excess of energy intake compared with
energy expenditure over time. What is surprising is how little we know about how
to alter this balance to prevent excess weight gain during the first two decades
of life. For example, the dietary factors that contribute to weight gain are
obscure. Dietary fat is probably not the culprit, at least in isolation.2
Other factors, such as dietary fiber or its relative, glycemic index, might be
more important, but long-term intervention studies are lacking.3
While the amount of physical activity predicts relative weight gain in childhood
and adolescence,4 less is known
about the modifiable determinants of activity levels. Even with knowledge of
such factors, we would still lack tested behavior change strategies to alter
them substantially.5 Considerable
interest exists in community-based approaches to increase physical activity
among populations, but such strategies are largely untested.6
Perhaps the best evidence for effective obesity prevention comes from
school-based trials to reduce levels of inactivity, chiefly television viewing,
although their costeffectiveness is still in question.7,8
Thus it is welcome news that breast-feeding may prevent excess weight gain later
in childhood. Rates of breast-feeding initiation and duration appear modifiable
over time; from a low of 25% in the 1970s, the proportion of women initiating
breast-feeding has risen to close to 65% in the late 1990s.9,10
However, fewer than 30% of women still breast-feed at 6 months postpartum, well
below the Healthy People 2010 goal of 50%.10
In addition, women of racial/ethnic minorities initiate breast-feeding at lower
rates than whites in the United States.
Of several recent studies suggesting a protective effect of having been
breast-fed on later obesity, 4 deserve particular mention because of relatively
large sample size, follow-up to at least preschool age, and adjustment for
important potential confounding factors. Three have been published previously11-13
and the fourth is the welcome addition by Toschke et al14
in this issue of The Journal. Despite somewhat different exposure and outcome
definitions, the 4 studies agree remarkably on the magnitude of risk reduction
for obesity comparing children who had been breast- versus formula-fed: adjusted
odds ratios ranged from 0.75 to 0.84. Two of the studies also showed that
increased duration of breast-feeding predicted lower rates of later obesity.11,13
Odds ratios for less severe overweight varied more.
The most important question about these studies is whether residual confounding
could explain the results. Although each of these analyses involved adjustment
for a number of traditional social and economic factors, as well as parental
adiposity in all but one, none of the studies directly measured the underlying
reasons why women of certain social or cultural backgrounds decided to feed
their infants in the way they did. These factors influencing a woman's decision
to breast-feed her baby may also be related to risk of later obesity. It is
somewhat comforting that Toschke et al.14
performed a secondary analysis showing that using continuous, rather than
categorical, forms of their adjustment variables did not alter the results, but
this fundamental limitation of existing observational studies remains. Future
observational studies would be stronger if they directly measured why women
choose a certain method of infant feeding. Data from an era when breast-feeding
was more common in lower socioeconomic strata might help. It is also possible
that now-planned follow-up of participants in a Belarussian randomized trial to
increase breast-feeding rates will address this limitation.15
Crossovers could introduce noise, however, and generalizability to countries
with higher rates of obesity would be an issue.
In the meantime, investigation of possible mechanisms for the beneficial effect
of breast-feeding could add evidence for valid and causal associations. Putative
mechanisms involve both behavioral and hormonal pathways. Compared with
bottle-fed infants, breastfed infants may be able to better communicate their
energy needs to the mother, resulting in more appropriate self-regulation of
energy intake later in childhood. The evidence for this hypothesis, however, is
meager, resting mainly on cross-sectional studies of toddlers and preschoolers
from select populations.16 The need
exists for longitudinal studies that carefully assess childhood growth as well
as parental control over infant feeding practices. Similarly, more information
is needed on the hormonal effects of breast-feeding that may influence long-term
energy metabolism. Studies now two decades old suggest effects on insulin
secretion,17,18
but recent or more detailed data are lacking.
For the research community, these improvements in epidemiologic studies and new
data from ancillary sciences from sociology to endocrinology are vital to
unraveling whether—and the extent to which—breast-feeding protects against later
obesity. Yet even today clinicians and policy makers should not ignore the
growing consistency of evidence that having been breast-fed may lower one's risk
of excess weight gain later in life. We are also in the felicitous situation
that for many other reasons, breast-feeding is the clear best choice for almost
all mothers and infants.9,10
Thus it makes sense to add potential obesity prevention to the list of
breast-feeding's benefits.
1. Pinhas-Hamiel O, Dolan LM, Daniels SR, Standiford D, Khoury PR,
Zeitler P. Increased incidence of non-insulin dependent diabetes mellitus
among children and adolescents. J Pediatr 1996;128:608-15.
4. Berkey CS, Rockett HRH, Field AE, Gillman MW, Frazier AL, Camargo
CA Jr, et al. Activity, dietary intake, and weight changes in a longitudinal
study of preadolescent and adolescent boys and girls. Pediatrics 2000;
105:e56.
5. Robinson TN. Obesity prevention. In: Chen C, Dietz WH, eds. Obesity
in childhood and adolescence. Philadelphia (PA): Vevey/Lipincott Williams and
Wilkins; 2002. p. 245-56.
6. United States Department of Health and Human Services, Centers for
Disease Control and Prevention, National Center for Chronic Disease Prevention
and Health Promotion. Promoting physical activity: a guide for community
action. Washington (DC): 1999.
7. Gortmaker SL, Peterson K, Wiecha J, Sobol AM, Dixit S, Fox MK, et
al. Reducing obesity via a school-based interdisciplinary intervention among
youth: Planet Health. Arch Pediatr Adolesc Med 1999;153:409-18.
9. Committee on Nutrition of the American Academy of Pediatrics.
Pediatric nutrition handbook. 4th ed. Elk Grove Village (IL): American Academy
of Pediatrics; 1998.
10. United States Department of Health and Human Services, Office on
Women's Health. Breastfeeding: HHS blueprint for action on breastfeeding.
Washington (DC): US Department of Health and Human Services; 2000.
11. Gillman MW, Rifas-Shiman SL, Camargo CA Jr, Berkey C, Frazier AL,
Rockett HRH, et al. Risk of overweight among adolescents who had been breast
fed as infants. JAMA 2001;285:2461-7.
13. von Kries R, Koletzko B, Sauerwald T, Von Mutius E, Barnert D,
Grunert V, et al. Breast feeding and obesity: cross sectional study. BMJ
1999;319:147-50.
14. Toschke AM, Vignerova J, Lhotska L, Osancova K, Koletzko B, von
Kries R. Overweight and obesity in 6- to 14-year-old Czech children in 1991:
protective effect of breast-feeding. J Pediatr 2002;141:764-9.
17. Lucas A, Sarson DL, Blackburn AM, Adrian TE, Aynsley-Green A,
Bloom SR. Breast vs bottle: endocrine responses are different with formula
feeding. Lancet 1980;1:1267-9.
18. Lucas A, Boyes S, Bloom SR, Aynsley-Green A. Metabolic and
endocrine responses to milk fed in six-day-old term infants: differences
between breast and cow's milk formula feeding. Acta Paediatr Scand
1981;70:195-200.
Department of Ambulatory Care and
Prevention
Harvard Medical School and Harvard Pilgrim Health Care, and
The Department of Nutrition
Harvard School of Public Health
Boston, MA 02215
Supported by a grant from the National
Institutes of Health (HL 68041).
Reprints not available from author. Please
address correspondence to: Matthew W. Gillman, MD, SM, Department of
Ambulatory Care and Prevention, Harvard Medical School/ Harvard Pilgrim Health
Care, 133 Brookline Ave, 6th Fl, Boston, MA 02215. E-mail:matthew_gillman@hms.harvard.edu
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