Anthropometric data were collected monthly from birth to 18 months as part of the Davis Area Research on Lactation, Infant Nutrition and Growth study, which followed infants who were either breast-fed or formula-fed during the first 12 months. The two cohorts were matched for parental socioeconomic status, education, ethnic group, and anthropometric characteristics and for infant sex and birth weight, and neither group was given solid foods before 4 months. While mean weight of formula-fed infants remained at or above the National Center for Health Statistics median throughout the first 18 months, mean weight of breast-fed infants dropped below the median beginning at 6 to 8 months and was significantly lower than that of the formula-fed group between 6 and 18 months. In contrast, length and head circumference values were similar between groups. Weight-for-length z scores were significantly different between 4 and 18 months, suggesting that breast-fed infants were leaner. The groups had similar weight gain during the first 3 months, but breast-fed infants gained less rapidly during the remainder of the first year: cumulative weight gain in the first 12 months was 0.65 kg less in the breast-fed group. Length gain was similar between groups. These results indicate that weight patterns of breast-fed infants, even in a population of high socioeconomic status, differ from current reference data and from those of formula-fed infants. Thus, new growth charts based on breast-fed infants are needed.
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