Energy intake, net energy output, is a determinant of body size in infants

Background: It has been proposed that the primary determinants of body weig ht at 1 y of age are genetic background, as represented by parental obesity , and low total energy expenditure. Objective: The objective was to determine the relative contributions of gen etic background and energy intake and expenditure as determinants of body w eight at 1 y of age. Design: Forty infants of obese and 38 infants of lean mothers, half boys an d half girls, were assessed at 3 mo of age for 10 risk factors for obesity: sex, risk group (obese or nonobese mothers), maternal and paternal body ma ss index, body weight, feeding mode (breast, bottle, or both), 3-d energy i ntake, nutritive sucking behavior during a test meal, total energy expendit ure, sleeping energy expenditure, and interactions among them. Results: The only difference between risk groups at baseline was that the h igh-risk group sucked mon vigorously during the test meal. Four measures ac counted for 62% of the variability in weight at 12 mo: 3-mo weight (41%, P = 0.0001), nutritive sucking behavior (9%, P = 0.0002), 3-d food intake (8% , P = 0.0002), and male sex (3%, P = 0.05). Food intake and sucking behavio r at 3 mo accounted for similar amounts of variability in weight-for-length , body fat, fat-free mass, and skinfold thickness at 12 mo. Contrary to exp ectations, neither total nor sleeping energy expenditure at 3 mo nor matern al obesity contributed to measures of body size at 12 mo. Conclusions: Energy intake contributes significantly to measures of body we ight and composition at 1 y of age; parental obesity and energy expenditure do not.