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

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.