Human protein requirement: policy issues

摘要

For most of the population of the world plants provide the main dietary source of proteins for consumption (Jackson & Margetts, 1993). Were there to be an absolute need to consume animal protein in order to achieve optimum health, this need would have very considerable implications for food security. Animal protein is expensive to produce in terms of human effort, resource consumption, land use, water and energy requirements. If there is an absolute need for animal protein consumption at even modest levels, it is unlikely in the short to medium term that self-sufficiency can be achieved (Waterlow et al. 1998). On the other hand, there is evidence that high levels of consumption of protein can lead to adverse effects, especially during pregnancy, and may accelerate the ageing process, although the evidence for and against there being an increased risk, or rate of disease progression, with higher patterns of consumption is not conclusive (Hu et al. 1999; Jackson, 1999a,b; Millward, 1999a,b). Dietary proteins have a physiological function in their own right during breast-feeding, but at all other times dietary proteins are used by the body as a source of amino acids, although they may be better absorbed as di- and tripeptides. Amino acids taken in the diet and formed in the body are utilised to satisfy the body's needs for individual amino acids for protein synthesis and other metabolic pathways. However, our understanding of the quantitative and qualitative demands by the body for individual amino acids is incomplete, and we have to make judgements based on a broad appreciation of the pattern of amino acids which the body needs. Thus, there is a great deal of work to be done in developing a sharper characterisation of the needs for each amino acid by age, gender and physiological and pathological state. This is the basic information which is required in order to determine the amount and pattern of dietary protein which best meets the needs of the body. In the absence of this information all other approaches to determine protein requirements have been based on indirect methods or broad generalisations about the response to the provision of different patterns and amounts of amino acids in the diet.