Relationship between Formula Concentration and Rate of Growth of Normal Infants

Abstract

The recent advent of ready-to-use infant formulas supplied in disposable units has made it feasible to record precise food intakes of normal infants living at home. Thirty-seven normal infants with birth weights of 2500 g or more were enrolled in a study designed to explore the relationship between formula concentration and growth rate during ad libitum feeding in the first 112 days of life. Thirty-two of the subjects completed the entire period of observation. The infants were divided into three groups according to diet and sex. Comparisons are made between two groups of male infants receiving formulas that were similar except for water content, one group being fed a formula that provided 133 kcal/100 ml whereas the other group received a formula providing 67 kcal/100 ml. Comparison of male and female infants receiving the same formula (67 kcal/100 ml) is also presented. In observations of male infants during the interval 8 to 42 days of age, feeding of the more concentrated formula was associated with smaller volume of food consumed but generally greater intake of calories. The greater calorie intakes were accompanied by greater rates of gain in length and weight; these differences were statistically significant. Rate of gain in weight per unit of calories consumed was not significantly different. Between 42 and 112 days of age, calorie intake per unit of body weight, and rates of gain in length and weight were nearly the same for the two groups of male infants. Calorie intake per unit of body weight, and rates of gain in length and weight were less for female than for male infants fed the same formula during the interval 8 to 42 days of age. Differences between the two groups in rate of gain in length but not in rate of gain in weight were statistically significant. Calorie intake per unit of body weight and rates of gain in length and weight were also less for females than for males during the interval 42 to 112 days of age. The regression of gain in weight (grams per day) on calorie intake (kilocalories per kilogram per day) for all males in the period 8 to 42 days of age was statistically significant. Using data from the present study, together with those from previously published reports, speculations are presented on the composition of the weight gained and on the partition of metabolizable energy into that for growth and that for maintenance. It is tentatively concluded that the composition of weight gained by the two groups of male infants was different: lipid appeared to account for a larger percentage of weight gain by infants receiving the higher calorie intakes. It is also tentatively concluded that energy requirements for maintenance per unit of body weight are less for female than for male infants receiving the same diet.