Summary of main results

Tables 3 and 4 summarize the results derived from the nitrogen balance studies. Table 5 shows that total plasma proteins decreased after nine days with an intake of 0.5 9 milk protein/kg/day and also after nine days with 0.75 9 soybean protein/kg/day.

Except for a decrease in urinary urea with the decrease in nitrogen intake, there were no consistent diet-related changes in the other biochemical indicators explored.

Rates of weight gain during the nine-day periods were slower with milk protein intakes of 0.5 9 milk protein/kg/day than with 1.00 or 1.25 g/kg/day (ANOVA: F_{3 34} = 3.473; least significant difference 13.1 g/day).

Although the mean weight gain was also lower with the lowest levels of soybean protein intakes, these did not differ from the higher levels because of the large inter individual variability.

TABLE 3. Data Derived from Nitrogen Balances: Milk

a "True" digestibility assumes obligatory faecal nitrogen loss of 20 mg/kg/day.
b Apparent balance = intake—urinary nitrogen—faecal nitrogen.
c Allowing 15 mg N/kg/day for growth and 9 mg N/kg/day for insensible losses.
d Using all data for the corresponding design; n = number of determinations.

TABLE 4. Data Derived from Nitrogen Balances: Soybean Protein Isolate

a, b, c, d See footnotes in table 3.

TABLE 5. Plasma Protein Concentrations with Different Levels of Protein Intake (g/dl)

a,b Differs from preceding protein intake (student's paired "t" test): a: p< 0.01; b: p<0.05.
c Proportion of children with decreased concentrations after nine days on the corresponding dietary protein intake.
* Basal period.

The RPV and RNR of the soybean protein isolate, compared with milk, were 83 per cent and 81 per cent, respectively.