Summary of main results

1. Energy Intake
During period 1, the men received 46 i 4 kcal/kg/day, and during period 2, their energy intake was increased to 58 i 4 kcal/kg/day.

2. Anthropometry
Table 3 shows the anthropometric data obtained during the study. All subjects except one lost weight. The remaining anthropometric indices did not show significant changes.

3. Urinary Nitrogen Excretion
Figure 1 and tables 4A and 4B show the daily urinary nitrogen losses. It should be noted that subject E.R. on day 6 did not comply with the experimental protocol and exercised heavily. We eliminated the abnormally high value obtained that day and, for computational purposes, replaced it with the mean obtained from days 5 and 7. A kinetic evaluation of the data is presented in Table 4A. Subject S.L. did not reach stability by day 10 and his data were not included to calculate the mean parameters of the equations. The asymptotically derived urinary nitrogen loss (P3) after stability had been reached was 35.8 mg N/kg/day. The mean time to stabilitY (tS) was 6.5 days. Data from subject H.R. on day 15 and from E.R. on day 13 were not included in the pooled regression analyses and daily means because these abnormally elevated values corresponded to days on which the conditions of the experimental protocol were not fully met. The regression analysis of nitrogen loss versus days with excess energy showed a trend toward decline in nitrogen loss.

TABLE 3. Anthropometric Measurements of Subjects Fed a Nitrogen-Free Diet at Two Levels of Energy Intake

* Mean ± S.D.

4. Other Urinary Excretions
Table 5 shows the mean urinary creatinine, urea nitrogen, and total nitrogen lost daily during the last five days of each period.

TABLE 4A. Kinetic Analysis of Daily Nitrogen Excretion in Subjects Fed a Nitrogen-Free Diet for Ten Days. Dietary energy intake: 46 kcal/kg/day.

* Subject S,L did not reach a stable nitrogen loss during this period. His data were not included in the means. P1 and P3 are expressed in mg N/kg/day; P2 is given in days—1; ts stands for days needed for stability.

TABLE 4B, Daily Nitrogen Excretion in Subjects Fed a Nitrogen-Free Diet with Excess Energy. Dietary energy intake: 58 ± 4 kcal/kg/day.

* Sample was lost.
** Data not included in the calculation because they deviated from expected values. Regression equations for (a) the complete set of data, and (b) for days 15 through 18: (a) v = - 1.50x + 55.4, r = - 0.39, p < 0.01; (b) - 3.31 x +8.52, r = - 0.46, p < 0.05.
*** Subjects did not complete study

5. Faecal Nitrogen Excretion
Table 5 also shows the mean daily faecal nitrogen excretion for both experimental periods.

6. Measurements in Serum
Table 6 summarizes the biochemical measurements obtained initially and at the end of each period.

7. Factorial Calculation
Table 7 shows the factorial calculation of mean protein requirements. Adding 30 per cent for individual variability as suggested in 1973 by FAD/WHO, the safe level of protein intake would be 0.62 g/kg/day.

TABLE 5. Obligatory Nitrogen Losses in Young Male Subjects Fed a Protein-Free Diet at Two Levels of Energy Intake

* Mean ± S.D.
** Faecal nitrogen losses for days 1 to 10.
*** Faecal nitrogen losses for days 11 to 18.

TABLE 6. Plasma Biochemical Measurements for Subjects Consuming a Nitrogen-Free Diet at Two Levels of Energy Intake

* Least significant difference to the indicated p value.

TABLE 7. Factorial Nitrogen Losses for Young Males Consuming a Nitrogen-Free Diet

1. Urinary nitrogen loss (mp N/kg/day) after asymptotic stabilization,
2. Obligatory urinary nitrogen losses for days 6 to 10.
3. Obligatory faecal nitrogen losses for days 1 to 10.
4. Assuming 5 mg N/kg/day for integumental and miscellaneous losses.