Protein requirements of infants and children: growth during recovery from malnutrition.

OBJECTIVE

To evaluate the adequacy of protein intakes now recommended as safe for infants and toddlers.

METHODS

Subjects were recovering malnourished infants, age 5.3 to 17.9 months, length age (LA) 2.5 to 6.4 months, weight age (WA) 1.5 to 5.2 months, weight/length (W/L) 78% to 100% of National Center for Health Statistics data; and toddlers age 11.4 to 31.6 months, LA 6.1 to 17.9 months, WA 3.9 to 12.0 months, W/L 79% to 99%. Infants were assigned at random to formulas with 5.5%, 6.7%, or 8.0% energy as 60:40 whey:casein protein. The 5.5% was based on FAO-WHO-UNU safe protein and average energy for ages 2.5 to 6.0 months. Toddlers received 4.7% (recommended for 6 to 18 months), 6.4%, or 8.0%. Identical concentrations (weight/kcal) of other nutrients were maintained; intakes were adjusted weekly to reach, in 90 days, the 50th percentile of weight for a LA 3 months greater than the initial one.

RESULTS

Infants consumed 125 +/- 11 (SD), 116 +/- 10, and 126 +/- kcal and 1.7 +/- 0.1, 1.9 +/- 0.2, and 2.5 +/- 0.3 g protein kg-1 . d-1; gained 2.4 +/- 0.7, 2.9 +/- 0.7, and 2.6 +/- 0.5 months in LA, and reached a W/L of 105 +/- 5, 103 +/- 6, and 105 +/- 5% of reference. Sum of four fat-folds (sigma FF) grew 13.1 +/- 6.9, 10.4 +/- 4.8, and 11.7 +/- 5.3 mm to 32.5 +/- 5.2, 31.7 +/- 4.7, and 30.5 +/- 5.5 mm; arm muscle areas (AMA) 57%, 51%, 70% to 1004 +/- 109, 1017 +/- 110, and 1004 +/- 116 mm2, still low; arm fat areas (AFA) 93%, 66%, and 93% to higher-than-normal 598 +/- 105, 610 +/- 101, and 541 +/- 116 mm2. Regression of intake on weight gain estimated energy for maintenance + activity to be 81.0 +/- 7.5 (SEM) kcal . kg-1 . d-1, and cost of gain (storage + metabolic cost) as 7.6 +/- 1.7 kcal/g, with no significant effect of % protein. Toddlers consumed 107 +/- 9, 103 +/- 12, and 105 +/- 10 kcal and 1.3 +/- 0.1, 1.6 +/- 0.2, and 2.1 +/- 0.2 g protein . kg-1 . d-1, gained 3.3 +/- 0.7, 2.9 +/- 0.6, and 3.3 +/- 0.7 months in LA; to a W/L of 102 +/- 1, 102 +/- 3, and 101 +/- 4%. Sigma FF grew 9.2 +/- 4.0, 7.4 +/- 4.3, and 6.0 +/- 3.8 to 28.9 +/- 5.2, 30.5 +/- 3.7, and 27.0 +/- 2.7 mm; AMA 31%, 33%, and 34% to 1121 +/- 115, 1124 +/- 110, and 1117 +/- 120 mm2; AFA 53%, 44%, and 45% to higher-than normal 578 +/- 106, 636 +/- 99, and 569 +/- 68 mm2. Cost of maintenance + activity was 70.8 +/- 3.8 (SEM) kcal . kg-1 . d-1, that of weight gain 9.7 +/- 1.35 kcal/g, with no effect of % protein.

CONCLUSIONS

Within age groups, there were no significant protein-related differences in growth. In both infants and toddlers, high-energy intakes resulted in mild obesity, with lean body mass still deficient. Protein intakes two SD below the means in the lowest protein/energy cells, 1.5 g . kg-1 . d-1 for infants and 1.1 g times kg-1 . d-1 for toddlers, should still be safe for nearly all children of comparable biological ages.