The effect of energy intake on nitrogen content of weight gained by recovering malnourished infants

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Abstract
The composition of weight gained by infants recovering from malnutrition was estimated. Paired dietary periods (2 g protein (N × 6.25) and 150 kcal/kg body weight per day) of a minimum of 21 days (≥30% in metabolic collection) were analyzed to determine the effect of protein source on the estimated percentage of N in the weight gained (%NΔWt) as follows: 7.5 mg N/kg per day for unmeasured losses was subtracted from mean apparent daily N retention (mg/kg per day) to estimate actual retention. This was divided by rate of weight gain (g/kg per day) to give %NΔWt. All infants became obese. During consumption of cow milk protein (n = 13) serum albumin concentration increased despite a low %NΔWt (2.07 ± 0.55%, X̄ ± SD). %NΔWt during nonmilk periods (n = 16) was equally low (2.01 ± 0.80%) but infants either decreased or failed to increase their serum albumin concentrations and showed a significant negative correlation between rate of weight gain and %NΔWt (r = −0.613, P < 0.02). A separate analysis was made of 16 paired dietary periods in which protein source and intake were constant but energy (E) intake differed by 25 to 50 kcal/kg per day. The %NΔWt at both intakes was calculated; %NΔWt of the extra weight gained at the higher E intake (relative to the lower E intake) and E cost of the additional weight were also estimated. On the average, an extra 3.93 ± 1.75 g/kg per day with an E cost of 8.39 ± 3.90 kcal/g was gained at the higher E intake. The %NΔWt in the additional weight gain was estimated to be only 0.80 ± 0.42%. Serum albumin concentrations were constant throughout. Both sets of data support the contention that the impressive gains in weight made by recovering malnourished infants are largely fat and that reconstitution of lean body mass does not occur equally well at all rates of weight gain. Protein status may be maintained if protein in the diet is quantitatively and qualitatively sufficient. If protein intake is low or of poor quality the development of obesity may be accompanied by a simultaneous deterioration of lean body composition.

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