Summary of the main results

1. Animal Protein Data
Table 3 shows the nitrogen-balance data. Four of the 11 subjects were classified as behaving atypically and are listed separately in table 3A.

TABLE 3. Nitrogen Balance in Subjects Consuming Protein Mainly of Animal Origin

Key:

Nl = nitrogen intake
UNE = urinary nitrogen excretion
FNE = faecal nitrogen excretion
TNB = total nitrogen excretion (assuming 5 mg/kg miscellaneous losses)
BV = biological value
D = digestibility

2. Results

1. Liver function was evaluated by measuring serum transaminase levels (SOOT) at the end of each period; although it was evident that there was a slight increase in the mean level of SGOT with increased protein intake, the mean value of SGOT between groups was not significantly different (ANOVA: p < 0.05).
2. The regression equation relating the nitrogen intake (Nl) with the urinary nitrogen excretion (UNE) was as follows (values in g/day): UNE = 2.78 + 0.308 Nl; thus, the UNE for 0 intake of protein would be 2.78 9. Assuming a mean weight of 60.7 kg, this corresponds to an obligatory urinary nitrogen excretion of 45.7 mg/kg, which is 7.7 mg/kg higher than that reported by Scrimshaw and others.
3. There are significant differences in total faecal nitrogen excretion with increasing levels of protein intake (p < 0.001). The regression equation relating faecal nitrogen excretion (FNE) with nitrogen intake (Nl) was: FNE = 0.77 + 0.21 (Nl) (values in g/day); thus, the obligatory nitrogen faecal excretion for zero protein intake was estimated to be 12.4 mg/kg, higher than the figure reported by Young et al. (V.R. Young, M.A. Hussein, and N.S. Scrimshaw, Nature, 218: 568 [1968] ), and just above the 12 mg/kg accepted by the FAD/WHO Committee.
4. Table 4 shows the data on nitrogen intake, urinary nitrogen excretion, faecal nitrogen excretion, and nitrogen balance expressed in mg/kg/day. The nitrogen balance increases significantly with an increase in nitrogen intake. The regression equation of the nitrogen intake (Nl) expressed in mg/kg/day on the true nitrogen balance (NB) was: NB = -65.84 + 0.50 (Nl).

TABLE 3A. Atypical Subjects

A close look at the individual data values shows that subject 01 never attained a positive nitrogen balance, and the slope of the regression level relating nitrogen intake with nitrogen balance was 0.35. Although the data for this individual still met the criteria outlined by the WHO-UNU guideline, they were not typical, and it is perhaps not wise to include the data for this subject in the calculations. He had a history of renal stones, and during the study he had a severe attack of renal lithiasis.

TABLE 4. Nitrogen Data for Subjects Consuming the Predominantly Vegetable Protein Diet 1

1 Excluding four ''atypical'' subjects.
* All values expressed in mg/kg/day.

The impression of the research team was that throughout the study the subject suffered from a chronic renal infection. This observation and other values considered by the team as errors in collection were deleted. The regression line relating the nitrogen balance (NB) with the nitrogen intake (Nl) after deleting the questionable data was found to be: NB = - 66.7 - 0.52 (Nl).