Obligatory urinary and faecal nitrogen losses in young Chilean men given two levels of dietary energy intake.

1. The obligatory nitrogen losses were measured in young adult males of the low socio-economic group, consuming an N-free diet at 192 kJ (46 kcal)/kg per d from day 1 to 10 and 243 kJ (58 kcal)/kg per d from day 11 to 18. 2. All subjects, except one, lost weight compatible with N loss. 3. A kinetic evaluation of the results showed that the asymptotically derived urinary N loss after stability had been reached was 35.8 mg N/kg per d. The mean time to stability was 6.5 d. The subjects showed a trend toward decline in N loss while consuming the high-energy N-free diet. 4. The obligatory faecal N loss for days 1-10 was 16.1 mg N/kg per d and 8 mg N/kg per d for days 11-18. 5. Based on the factorial approach the total obligatory N loss of our subjects, for the initial 10 d, was 57.5 mg N/kg per d.