Although breast milk is recommended exclusively until 6 months of age, two-thirds of infants in the U.S. are fed infant formula. Despite an almost identical energy density between infant formula and breast milk, formula fed infants experience greater weight gain in the first year of life. The investigators propose that unintentional overfeeding, of nearly one additional day of calories per week, due to the "over-scooping" of powdered formula contributes significantly to this phenomenon and potentially to the early development of childhood obesity, a significant public health problem.