Energy intake, not energy output, is a determinant of body size in infants

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Abstract
Background: It has been proposed that the primary determinants of body weight 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 genetic background and energy intake and expenditure as determinants of body weight at 1 y of age. Design: Forty infants of obese and 38 infants of lean mothers, half boys and 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 mass index, body weight, feeding mode (breast, bottle, or both), 3-d energy intake, nutritive sucking behavior during a test meal, total energy expenditure, sleeping energy expenditure, and interactions among them. Results: The only difference between risk groups at baseline was that the high-risk group sucked more vigorously during the test meal. Four measures accounted 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 behavior 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 expectations, neither total nor sleeping energy expenditure at 3 mo nor maternal obesity contributed to measures of body size at 12 mo. Conclusions: Energy intake contributes significantly to measures of body weight and composition at 1 y of age; parental obesity and energy expenditure do not.