Childhood and adult obesity has reached epidemic proportions in the US. Obesity causes serious chronic illness, including adult and adolescent-onset, non-insulin dependent, Type II diabetes. Type II diabetes is associated with the very same life threatening, metabolic and cardiovascular complications as insulin dependent, Type I diabetes which begins much earlier in childhood. Hispanic, African-American, Native American, Asian-American and Pacific Islander groups are at especially high risk for developing Type II diabetes. Prevention of obesity is now a major public health focus in the US.

Obesity ultimately arises from an imbalance between food intake and energy output. The etiology of obesity is multifactorial - a complex interplay between genetics, lifestyle, behavior, physiology and culture. Because obesity often begins in childhood, much attention has recently focused on the possible fetal and early childhood causes of obesity, especially upon the contribution of early infant feeding.

The beneficial effect of breastfeeding may be via long-term, metabolic, hormonal and behavioral effects on satiety and energy expenditure, possibly by more appropriately matching appetite and food intake with energy expenditure. It is hypothesized that breastfed babies develop better methods of self-regulating food intake compared to formula/bottle fed infants. Energy balance and body composition are under neuroendocrine control by gastrointestinal (insulin, cholecystokinin), tissue (leptin), endocrine (norepinephrine) and neurologic (serotonin, growth hormone) hormones. It is possible that bioactive components or specific nutrients present in breastmilk, independent from the act of breastfeeding itself, confer specific, long-term protection by altering the hormonal and metabolic environment of the infant. As yet unidentified, subtle, socio-cultural differences between mothers who do and do not decide to breastfeed, or physiologic differences between those infants who receive breastmilk vs. formula from the bottle, have not been addressed in any published study.

Breastfeeding, compared to formula feeding, will not prevent obesity. However, even if the protective effect of breastfeeding alone on the prevalence of obesity is small, the overall public health impact on the prevalence of childhood and adult obesity would be substantial if all US babies were breastfed as currently recommended for at least 6 months.

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