Breast Milk and Childhood Obesity: The Czechs Weigh In

Overweight and Obesity in 6-to 14-Year-Old Czech Children in 1991: Protective Effect of Breast-Feeding. Toschke AM, Vignerova J, Lhotska L, Osancova K, Koletzko B, and vonKries R. J Pediatr 2002;141:764–9. Summary: This is a cross-sectional study of survey data collected in 1991 in the Czech Republic on 33,768 school-aged children 6 to 14 years old (1). Retrospective data on the duration of breast-feeding was collected at the time of the survey, although no distinction was made between exclusive and partial breast-feeding. Overall, 97.7% of parents completed the questionnaires, and 90.7% of families breast-fed their children at least partially. Height and weight were measured in school by physical education teachers with similar equipment. Children were classified as overweight (BMI >90th percentile) or obese (BMI >97th percentile) based upon within-sample cut-off ranges. The prevalence of overweight and obesity was lower in breast-fed infants compared with never breast-fed infants [overweight: 0.80 (0.71–0.90); obesity: 0.80 (0.66–0.96)]. Nevertheless, the differences were relatively small (i.e., obesity among breast-fed children was 4.4% compared with 3.2% for never breast-fed children). Similar effects of breast-feeding on weight status were seen at all ages and were independent of parental education, obesity, maternal smoking, television viewing, and physical activity. However, parental obesity [OR: 3.46 (3.07–3.90)], high birth weight [OR: 1.93 (1.62–2.31)], daily television hours [OR: 1.49 (1.32–1.69)], and sports participation [OR: 0.53 (0.46–0.62)] were all better predictors of childhood obesity than was exposure to breast milk. Comment: This large epidemiologic study provides descriptive evidence of an association between breast-feeding in infancy and a lower prevalence of childhood obesity. The findings agree with three other large, epidemiologic studies (Fig. 1) relating breast-feeding in infancy to a lower prevalence of later obesity (2–4). The highly consistent results from different study populations provide strong evidence for the statement that breast-feeding protects against obesity.FIG. 1.: Studies relating breast-feeding in infancy to a lower prevalence of later obesity.There are many possible explanations for the apparent protective effect of breast-feeding against obesity. Infants who breast-feed may be better able to regulate the amount of milk they consume than formula-fed infants. Feeding behavior of breast-fed infants is largely dependent on the infant, whereas feeding behavior of formula-fed infants may be more dependent on parental expectations. The increased length and weight of formula-fed infants in infancy (5) certainly suggests that formula-fed infants are overfed. Evidence is accumulating that both prenatal and postnatal exposure of infants to varied flavors affects infant feeding behavior (6). Specifically, infants who had exposure to the flavor of carrots in either amniotic fluid or breast milk reacted less negatively when offered carrot-flavored cereal and appeared to enjoy the cereal more than did the nonexposed control subjects. Studies by Sullivan and Birch suggest that breast-fed infants are more adventuresome in sampling previously untasted foods (7). Because the taste of breast milk varies considerably, depending on the maternal diet (8), infants who are breast-fed may be more likely to accept fruits and vegetables when they are introduced during infancy or early childhood. There is speculation that breast milk may contain bioactive factors that alter fat deposition or energy expenditure. The physiologic significance of leptin, insulin-like growth factors, somatostatin, and other growth-related hormones in breast milk also remains uncertain. Nevertheless, differences in endocrine response to breast milk and formula feeding have been documented (9). For example, the increased glucose and insulin levels in the breast milk of mothers with diabetes may actually increase the risk of subsequent obesity in childhood (10). A note of caution needs to be sounded about accepting the results of any large, epidemiologic study. Rather than being causally related to later protection against obesity, the presence of breast-feeding may actually be a marker for other factors related to leanness. The authors argue that the relatively homogeneous living conditions in Czechoslovakia in the 1970s and 1980s minimized the effect of confounding social factors on the breast-feeding/obesity relationship they found. However, the actual timing of the study in 1991, 2 years after the “Velvet Revolution” when the Czech economy entered a sharp decline, raises the possibility that social and economic differences among families may have produced the study results. The fact that only 9.3% of children in the current study were never breast-fed raises the concern that families who breast-fed their children were significantly different from those who did not breast-feed. In this study, the children who were not breast-fed were more likely to watch TV for longer hours per day, were less likely to eat fruit, and were more likely to have parents who were obese, of lower education, and who smoked. The lack of a direct relationship between leanness and duration of breast-feeding also argues against a direct protective effect of breast milk. In this study, children breast-fed for less than 1 month had lower rates of later obesity than did children breast-fed for more than 6 months. In summary, this epidemiologic study supports the hypothesis that breast-feeding protects against later childhood obesity. While the overall impact of breast-feeding on childhood obesity may be small in comparison to other modifiable risk factors, the evidence of long-term benefit provided in this study is a welcome buttress to the recommendation we make daily (i.e., that breast-feeding is the best nutrition for infants). Richard Strauss UMG Department of Pediatric GI New Brunswick, New Jersey

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