Short-term studies, (papers 26–27) following the standard protocol, were presented, and their data are summarized in Table XII. Other related results were also discussed.
In Chile, seven preschool children (mean age 45 ± 10.5 months) were studied to estimate protein requirements, comparing milk and soy-isolate proteins, and using four-day balance periods preceded by four-day period of adaptation to the test diets. Milk and soy-isolate protein were given following a descending order (1.50, 1.25, 1.0, 0.25 g/kg/day), while the energy intake was kept constant at 100 kcal/kg/day. Mean protein intake to retain 24 mg N/kg/day was 0.99 g for soy protein/kg/day and 0.71 g kg/day of milk protein. Incorporating the variability of individual intercepts by adding 2 S.D., the corresponding requirement for soy and milk are 1.23 and 1.07 g/kg/day respectively, quite similar to current FAO/WHO figures for this age group.
These results differ from a previous study by Torun et al. using similar protein sources in younger children. These authors used a cross-over experimental design (ascending and descending) with protein intakes of 2.00, 1.25, 1.00, 0.25 and 0.50. Their mean nitrogen requirement to retain 24 mg N/kg/day (allowing for integumental losses and nitrogen retention for growth) were 0.61 g (98 mg N) of milk protein/ kg/day and 0.75 g (120 mg N) of soy isolate kg/day. The safe level of intake was established at 0.94 g milk protein/kg/day, or 1.01 g soy isolate protein kg/day. These values are lower than the 1.19 g milk protein/kg/day currently suggested by FAO/WHO.
| Country/ Investigator | Exper. Design | No. of Subjects | Age (mo.) | Energy Intake (Kcal/) kg/day) | Protein Intake (G/kg/day) | Protein Source | Digestibility (A-T) | Nitrogen Balance (mg/kg/day) | Change in Weight | Mean N Requirement (mg N/kg/day) | Protein Safe Intake (+2SD) (g/kg/day) |
| Chile (Egaña) | |||||||||||
| a) Soy Isolate | Descend | 7 | 45±10 | 100 | 1.5–7.5 | Soy | 69–83 (A) | 63.0-0.0 | No | 162±263 | 1.34 |
| b) Milk | 7 | 1.5–7.5 | Milk | 74–83 (A) | 90–28 | No | 116±28 | 1.07 | |||
| Guatamala (Torun et al.) | |||||||||||
| a) Soy Isolate | Ascend | 10 | 23±4 | 100 | 0.5–1.25 | Soy | 94 (T) | ↑ | 1203 | -1.01 | |
| b) Milk | Descend | 10 | 2.0±0.5 | Milk | 94 (T) | ↓ | 98 | 0.94 | |||
| Philippines (Intengan) | |||||||||||
| Ascend | 4 | 23–29 | 100 | 10.1-1.75 | Rice-Bean | 57–62 (T) | 152 | ↑↓ | 1646 | 1.43 |
All studies performed in metabolic unit - retention
1) A: Apparent digestibility
T: True digestibility
2) Descending design: 1.5, 1.25, 1.0, 0.75 g protein/kg/day
3) Calculated at 24 mg/kg N retention /kg/day intercept
4) Descending design: 2.0, 1.25, 1.0, 0.75, 0.5 g/protein/kg/day
Ascending design: 1.5, 0.5, 0.75, 1.0, 1.25 g/protein/kg/day
5) Ascending design: 0.75, 1.0, 1.25, 1.5, 1.75, 2.0 g/protein/kg/ rice and mung bean protein
6) Calculated at the 0 mg N/kg/day intercept
Data from the Philippines were presented on short-term balance studies in five children 23–29 months old, some of them malnourished at the time of the study. Diet was based on rice and mung bean providing a fixed energy intake of 100 Kcal/kg/day. The experimental design was of the ascending type, with protein intake starting at .75 g/kg/day reaching a maximum of 2.0 g at .25 g intervals. At intakes under 1 g/kg/day, all subjects were in negative balance. The safe level of intake for 97.57 percent of this population was estimated to be 229 mg N (or 1.43 g protein) kg/day. Although this seems high, the authors suggest that they could be due to the higher fiber content and lower digestibility of diets with the highest protein content (mung bean). The apparent digestibilities were only 57–62 percent, and faecal nitrogen was always higher than urinary nitrogen.
Tontisirin presented data from short- and long-term studies in children in Thailand (paper 28). The short-term study was performed in infants 9 to 36 months in a metabolic unit setting. Children were fed the typical Thai weaning diet consisting of rice, fish, .and banana. In these studies, children were given a fixed amount of protein (1.7 g/kg/day), while energy intakes were varied from 87 to 118 Kcal/kg/day.
At the lowest level of energy intake (82 Kcal/kg/day), N retention and weight gain were low. At energy intakes of 100 and 118 Kcal/day, N retention was greater than 60 mg/kg/day, and daily weight gain was over 20 g. These data suggest that present safe levels of protein intake (FAO/WHO, 1973) are adequate for this age group provided that energy intake is 100 Kcal/kg/day or higher.
Two long-term studies (papers 28, 23) conducted in children were presented. Their data are summarized in Table XIII and discussed below.
In Thailand six normal infants 8 to 12 months old were studied as they were recovering from malnutrition. Children were followed for up to 120 days in a metabolic unit and fed, throughout the study, a diet providing 1.7 g protein/kg/ day and 100 Kcal/kg/day. Fat provided 10% of the total energy in their diet; protein digestibility was about 66 to 74 percent, and energy absorption was 93 to 95 percent of intake. Metabolic balance studies were performed during the last three days of each 30-day period into which the study was divided.
Energy intakes were close to 100 Kcal/Kg/day and protein was fed at a level of 1.8 g/kg/day during the first two months of follow-up. For the last two months the energy intakes dropped to 94 Kcal/kg/day, and daily protein intake was 1.7 g/kg/day. N retentions of 85 to 100 mg/kg/day were observed initially. During the last two months N retained ranged from 46 to 71 mg/kg/day. Weight gains were close to 10 g/day for the first two months and about 8 g/day for the last two months.
The authors conclude that the recommended safe level of protein intake (2) is adequate for infants provided that energy intakes are 100 Kcal/kg/day or more. These conclusions are, however, confounded by the fact that some of the children studied were not fully recovered from malnutrition, although their weight/height ratios were close to normal. The higher weight gains and nitrogen retentions in the first two months could be part of catch-up growth and not exclusively related to higher energy and protein intakes. Weight for height is not a reliable index of normal nutritional status in children below 12 months, and weight gain should compared to the weight gain of normal infants of the same body weight and age.
| Country and Investigator | No. of Subj. | Duration (days) | Envir. Cond. | Protein intake | Mean N-balance (0 + 10 mg N/kg/day) | Energy Intake (Kcal/kg/ day) | Body weight Changes | Other Measurement (see progress) | |
| g/kg/day mean | A/V | ||||||||
| Guatamala (Torun) | 9M, 4F (15–40 mo) | 63–98 | Metab. | 1.99 (mixed) | 13/87 | 95±75 | 91–103* | 10–15** | No adverse effects |
| Thailand (Tontisirin) | 6M | 120 | Metab. | 1.70 (mixed) | 30/70 | 46–100 | 100 | 8–11** | No adverse effects |
* Net energy intake.
** Some subjects had periods of higher rate of weight gain than normal due to catch-up growth.
In Guatamala nine boys and four girls, 15 to 40 months old, most of them not fully recovered from malnutrition (defined as weight/height under 92%) were studied for 9–14 weeks. These children were fed a diet typical of low-income rural populations in Central America. Children could eat as much as they wanted of the corn/bean diet, but animal protein was fixed not to exceed 16 percent of the total. Net energy intake was computed individually by subtracting faecal from food energy measured by bomb calorimetry.
The aim of the study was to determine if typical diets are capable of sustaining normal growth if enough is available. Black beans and corn provided 70 percent of the dietary protein, other vegetable, 17 %, and animal protein 13%.
Nine children with weights for height below 92% of standard gained weight more rapidly than those with normal W/H. The values in the absence of illness were 2.5 and 1.3 g/kg/day, respectively. Children of comparable height gain 0.7 g/kg/day. Gain in length was, on the average, below the 0.33 mm/day expected for normal children of the same size. During episodes of infection, weekly consumption of solid foods dropped by about 10 percent and weight gain was slower. Energy expenditure derived from the heart rate oxygen consumption relationship was 65.8 ± 7.0 Kcal/kg, with a resulting balance of + 31.5 Kcal/day.
The Thai and Guatemalan studies show that local diets are capable of sustaining normal growth of children when given in appropriate amounts and proportions. However, all the studies were done in the setting of a metabolic ward under closely supervised conditions and utmost care. The conclusions of these studies should be extrapolated to village conditions with great caution, since a multitude of factors may affect, in a positive or negative way, food intake or nutrient utilization. Most important are the frequency of infections and the low energy and protein density of many local diets.
Jackson (paper 25) presented a preliminary report of a nitrogen flux study, on normal or recuperated PEM infants, measured at two fixed levels of protein intake (0.7 or 1.7 g/kg/day) and at three levels of energy intakes (80, 90, and 100 Kcal/kg/day) and provided interesting insights into the possible processes of adaptation to changes in dietary protein and energy. There was remarkable variability in kinetic measurements on a given diet. This was consistently greater than variation within a single individual on different diets. Total Nitrogen flux appears to be dependent on protein intake, being half on an intake of 0.7 g of that on 1.7 g protein. In three children given an adequate protein intake, flux was not modified by decreasing energy from 100 to 90 and appeared to increase as energy intakes fall to 80 Kcal/kg/day. The changes in whole body protein breakdown appear to be more sensitive to the level of dietary protein and energy. Although very limited by the few subjects and great variability, this study from Jamaica suggests that dynamic measurements of protein metabolism may be useful to assess adequacy of protein-energy intakes.
