Published online by Cambridge University Press: 24 July 2007
1. The net protein utilization (npu, the percentage of dietary nitrogen retained in the body, allowance being made for endogenous urinary and faecal N) of diets composed of Nigerian foodstuffs, based on rice, sorghum (Sorghum sativa) or cassava (Manihot utilissima), was compared to that of a minimal protein diet used to determine endogenous N excretion, supplemented with whole egg. The addition of dl-methionine and l-tryptophan to the rice diet produced a small but non-significant increase in npu, whereas the addition of dl-methionine to the cassava diet produced a very significant increase in npu. The npu of a diet based on home-pounded, winnowed, sorghum flour was higher than that of a diet based on milled whole-meal sorghum due to the low digestibility of the latter diet.
2. The digestibility of the rice and cassava diets were the same, although the total crude fibre content of the rice diets was lower than that of the cassava diets.
3. Nigerian men used the proteins of the egg diet and of mixed diets based on rice, sorghum and cassava more efficiently than predicted by applying methods recommended by the FAO/WHO ad hoc Expert Committee on Energy and Protein Requirements (FAO/WHO, 1973).
4. The recommendations of that Committee (FAO/WHO, 1973) to reduce the amounts of sulphur amino acids and tryptophan, contained in the ‘provisional pattern of amino acids’ proposed by the FAO Committee on Protein Requirements (FAO, 1957), are supported, but the increases in lysine and threonine are not supported, by the present results.