Samuel J. Fomon

HUMAN BODY COMPOSITION

Although it is self-evident that the study of human nutrition has as its goal the optimal nutrition of man, the nutritional status of the body best suited to optimal performance, i.e., optimal nutrition, has unfortunately not yet been satisfactorily defined. Body composition of animals may be measured by direct chemical analysis and correlated with dietary intake and with the various aspects of performance; studies of body composition of living man, on the other hand, must rely on indirect measure ments. The following two reports, which give an account of the current status of the attack on the difficult task of measuring body composition in living man, are sponsored by the Committee on Nutrition to call attention to the resurgence of effort in this field during recent years. A fuller knowledge of the gross composition of the human body and its relation to preceding diet will constitute a significant step towards realization of the ultimate goal of nutritional science. Even then, a particular body composition will be of importance primarily in terms of functional performance. The availability of newer techniques should do much to stimulate physicians and nutritionists in defining body composition as an essential step in arriving at a more exact definition of optimal nutrition.

Effect of iron fortification of infant formula on trace mineral absorption

This study was designed to examine whether iron fortification of infant formulas has an effect on utilization of other nutrients, particularly the trace elements zinc and copper. Metabolic balance studies were performed with seven normal infants who were between 43 and 420 days of age. Two formulas of nearly identical composition except for iron concentration (10.2 and 2.5 mg/L) were fed. Each infant had four balance studies performed, two while being fed formula 10.2 and two while being fed formula 2.5, in an alternating sequence. No effect of formula iron concentration was evident on absorption and/or retention of nitrogen, fat, calcium, and magnesium. Although absorption of phosphorus was significantly (p less than 0.05) less with formula 10.2 than formula 2.5, the difference was trivial. No effect on absorption of zinc was seen. However, absorption of copper was only 13.4% (SD 13.0) of intake when formula 10.2 was fed, compared with 27.5% (SD 15.3) of intake when formula 2.5 was fed. The difference was statistically significant (p less than 0.01). We conclude that iron in amounts present in iron-fortified formulas has a measurable effect on copper utilization. Because the magnitude of the effect is relatively small, we doubt that the finding is clinically relevant.

Fluid intake, renal solute load, and water balance in infancy.

A simple, largely empiric method for estimating renal solute load is proposed. Utilizing this method, examples of urine concentration and water balance are described in hypothetic infants receiving various feedings at differing volumes of intake and with normal or increased extrarenal losses of fluid. Circumstances in which water balance must be a primary consideration in infant feeding are discussed.

Cow milk feeding in infancy: gastrointestinal blood loss and iron nutritional status.

Eighty-one normal infants were studied between 112 and 196 days of age. Thirty-nine infants were fed pasteurized cow milk and the remainder were fed either Enfamil or heat-treated cow milk. During the age interval of 112 to 140 days, the proportion of infants with guaiac-positive stools was significantly (P less than 0.01) greater among infants fed pasteurized cow milk than among those fed Enfamil or heat-treated cow milk. Similarly, infants fed cow milk had a significantly (P less than 0.001) greater number of guaiac-positive stools than did the other infants. After 140 days of age, there was no difference between feeding groups in the number of guaiac-positive stools. No significant differences were observed in mean hemoglobin, hematocrit, serum iron, total iron-binding capacity, or transferrin saturation between feeding groups nor between infants with and those without guaiac-positive stools, It is concluded that pasteurized cow milk should not be fed before 140 days of age.

Gain in weight and length during early infancy.

Although rate of growth is generally recognized as a valuable indicator of health status, few reference data are available for gain in weight or length during the period of most growth in infancy. We have therefore summarized our data concerning gains in length and weight of 203 breast-fed males, 216 breast-fed females, 380 formula-fed males, and 340 formula-fed females. Seven sets of measurements (at ages 8, 14, 28, 42, 56, 84 and 112 days) were made with each infant. The 5th, 10th, 25th, 50th, 75th, 90th and 95th centile values together with the means and standard deviations are presented for selected age intervals on a feeding-specific (i.e. breast-fed or formula-fed) and sex-specific basis. We believe that these data will be useful as a reference for interpreting results of infant studies.

Urination during the First Three Years of Life

Urination was studied in 15 normal infants and young children on 150 occasions in the course of metabolic balance studies. With increasing age, mean urine volume increased if expressed as ml/day and decreased if expressed as ml/kg/day. Urine volume was correlated with volume of intake (r = 0.697) and accounted for a similar percentage of volume of intake irrespective of age. The mean number of voidings decreased from 20.1 per day during the first month of life to 10.8 per day in the third year of life. Absolute voiding size increased with age but did not change per unit of body weight. This study establishes urine volume, voiding frequency and voiding size of normal children during the first 3 years of life.

Requirements for protein and essential amino acids in early infancy. Studies with a soy-isolate formula.

Thirteen normal female infants were observed from 8 through 111 days of age while receiving a diet providing 1.62 g of protein per 100 kcal, almost entirely from soy‐isolate. Clinical observations, growth rates and serum concentrations of albumin were similar to those of female infants fed milk‐based formulas providing greater intakes of protein. On the basis of these findings, it is assumed that the requirements for protein and essential amino acids of these infants were no greater than the amounts consumed. Reasons for preferring to express requirements for proteins and amino acids per unit of calorie intake rather than per unit of body weight are presented.

Potential Renal Solute Load of Infant Formulas

The potential renal solute load (PRSL) of infant feedings is the sum of dietary nitrogen (expressed as mmol of urea, i.e., mg nitrogen divided by 28), sodium, potassium, chloride and phosphorus. The PRSL determines the renal solute load, and, therefore, the osmolar concentration of the urine. When water intake is reduced and/or water losses are increased, the renal concentrating ability may be exceeded, and negative water balance (dehydration) may ensue. Under these circumstances, feedings providing high PRSL lead more rapidly to dehydration than do feedings providing lower PRSL. On the basis of simulated clinical situations and epidemiologic data, it is concluded that conventional infant formulas (PRSL 135-177 mosmol/l, or 20-26 mosmol/100 kcal) provide a satisfactory margin of safety. A feeding providing the upper limits for concentrations of protein and electrolytes specified by the Food and Drug Administration rule does not afford a satisfactory margin of safety. It is recommended that the upper limit for protein content of infant formulas be decreased from 4.5 g/100 kcal to 3.2 g/100 kcal and that an upper limit for phosphorus concentration of infant formulas be set at 93 mg/100 kcal. Maximum PRSL will then be 221 mosmol/l (33 mosmol/100 kcal).

Skim milk in infant feeding.

Abstract Ninety‐four infants were enrolled at 112 days of age in a study of food intake and growth and 88 were considered to have completed satisfactorily the planned 56 days of observation. The infants lived at home. Feedings consisted of a commercially available formula (Similac, 67 kcal/100 ml) or a slightly modified skim milk (Formula 305, 36 kcal/100 ml) and commercially prepared strained foods. Energy intake and gain in weight were significantly greater by infants fed Similac than by those fed Formula 305. Gain in length was nearly identical in the two feeding groups. During the 56 days of observation, triceps and subscapular skin‐fold thicknesses changed little in infants fed Similac but decreased approximately 25% in infants fed Formula 305. It is suggested that body fat stores of infants fed Formula 305 were mobilized to permit growth of fat‐free tissue.

Absorption and Retention of Dietary and Supplemental Fluoride by Infants

There is a widespread belief that an adequate intake of fluoride during the pre-eruptive stage of enamel formation (i. e., from the diet in frequent small doses throughout the day) will be protective against caries in later life. To obtain data on bio-availability and retention of fluoride in one age group (infants), we studied 3 treatment regimens: In Regimen A, small amounts of fluoride were obtained from the diet in frequent doses throughout the day; in Regimen B, a fluoride supplement (0.25 mg) was given once each day with a feeding; Regimen C was similar to regimen B except that the fluoride supplement was given 1 h before a feeding. For the 3 regimens, the respective mean absorptions of fluoride were 90.1, 88.9, and 96.0% of intake, and the respective retentions were 12.5, 47.1, and 52.3% of intake. Neither the difference in absorption nor the difference in retention between regimens B and C was statistically significant. By subtracting the background urinary excretion of fluoride (i.e., excretion of fluoride while diet was the sole source of fluoride) from the excretion after administration of the fluoride supplement, we calculated that 68.1% of the supplement was retained in Regimen B and 73.0% of the supplement in Regimen C. The difference was not significant.