Human protein requirements: obligatory urinary and faecal nitrogen losses and the factorial estimation of protein needs of Nigerian male adults

Abstract

1. The present study was designed to use the factorial approach to estimate protein requirements of Nigerian male adults by measuring obligatory nitrogen losses via urine, faeces and sweat when N intake was very low and energy intake adequate.2. Eight adult men from Osegere village near Ibadan and seven medical students from the University of Ibadan, who volunteered to participate as subjects in the study, were given a low-protein diet (based on staple foods habitually consumed by subjects) for 10 d. Mean daily total protein intake was 4.68 g while that of energy was 0.2 MJ/kg body-weight. After an initial 5 d adaptation period, 24 h urine and faeces were collected in marked containers for five consecutive days for N determination. N losses from the skin were also determined in the village adults.3. Mean daily urinary, faecal and sweat N losses (mg N/kg body-weight) were 45.88 (SD 4.84), 21.79 (SD4.19), and 7.46 (SD1.71) from the village adults. The corresponding urinary and faecal N losses from the university students were 43.45 (SD 2.28) and 18.32 (SD4.66) (sweat N loss not measured). Thus the total daily obligatory N losses (per kg body-weight) from the village adults and university students were 75.13 and 69.23 mg N respectively (assuming a sweat N loss of 7.46 mg for the university students). After adjusting for requirement and making a 30% allowance for individual variability, the safe level of protein intake was calculated to be 0.78 and 0.73 g protein/kg body-weight for the village men and university students respectively.4. These values suggest that the Joint FAO/WHO ad hoc Expert Committee (1973) safe allowance of 0.57 g egg protein/kg per d is not sufficient for most young adults in this environment when energy intake is adequate.