The role of breastfeeding in obesity

Despite the high prevalence of obesity among children in industrialized countries, the causes of obesity are poorly delineated. The negative effects of childhood obesity are substantial, including its persistence into adulthood and associated morbidity, such as impaired glucose tolerance, type 2 diabetes, hypertension, dyslipidemia, and psychosocial stress. 11 Obesity is a multifactorial disease arising from complex interactions between genes and the environment. Prenatal and postnatal development may have a role in later development of obesity. Early infant nutrition is one of the most powerful environment factors that determine early growth and development, and it may also influence gene expression. Investigators have hypothesized that breastfeeding may be protective against obesity. 19 The potential role and plausible biological mechanisms of breastfeeding in the development of obesity must be considered in conjunction with genetic and environmental determinants of obesity. Plausible biological mechanisms underlying the protective role of breastfeeding against obesity are based on the unique composition of human milk, suckling experience, and metabolic and physiologic responses to human milk. 19 The nutrient composition of human milk is qualitatively and quantitatively different from infant formula. Besides its unique nutrient composition, human milk contains bioactive substances that may influence adipocyte differentiation and proliferation. Investigators have speculated that infants' ability to regulate intake, or the caretakers' encouragement to feed, differ between breastfed and formula-fed infants, which may alter later regulation of intake. Over the past several decades, infant formula contents and food supplementation practices have changed, 46 confounding the interpretation of epidemiologic studies in this area. Differences in the growth pattern of breastfed and formula-fed infants during the period of exclusive milk-feeding are well recognized and have been attributed to differences in nutrient intake. 47 In studies with clearly defined feeding groups and sufficient sample sizes, rates of weight gain were lower in breastfed than in formula-fed infants. Breastfed infants consume not only less energy than do formula-fed infants but also disproportionately less protein and fewer micronutrients. 5,9,31,22 Higher rates of infantile obesity in formula-fed compared with breastfed infants, however, have not been demonstrated. Dubois et al 13 characterized obese infants at 6 months of age and found they were breastfed as often as the normal-weight infants. Studies comparing the body composition of breastfed and formula-fed infants are fewer and less consistent. Greater increases in skinfolds in breastfed than in formula-fed infants were reported in early 8,33 and later 37 infancy, in contrast to other studies that detected greater skinfold increases in formula-fed infants in early 9,39,49 and later 10 infancy. Many studies have failed to detect differences between feeding groups. 6,15,16,20,24,31,36 A few studies comparing breastfed and formula-fed infants used in vivo measurements of body composition. Bellu et al 3 used total body electric conductivity (TOBEC) to measure the body composition of breast- fed and formula-fed infants at 12 months of age and reported lower weight and body fat mass among the breastfed infants; however, these infants were significantly smaller at birth. A subsequent report by de Bruin et al 9 involved the use of TOBEC in a 12-month, longitudinal study comparing 23 breastfed with 23 formula-fed infants. Higher weight gains between 1 and 4 months in formula-fed girls resulted in significantly higher fat-free mass and fat mass, but not percentage of fat mass, at 4 and 8 months of age. The author's study 6 of the effects of infant feeding mode showed higher fat mass and percentage of fat mass in breastfed than in formula-fed infants at 3 and 9 months of age based on a multicomponent model of total body water, total body potassium, bone mineral content and TOBEC, but no differences at 12 and 24 months of age. To address whether differences in early growth patterns or metabolic regulation of breastfed and formula-fed infants may influence later growth and adiposity, this article examines anthropometric studies on tracking of body size and other determinants of childhood and adult obesity. Then, studies on the association between breastfeeding and the development of obesity later in childhood and adulthood are examined.