The nutritional value of plant-based diets in relation to human amino acid and protein requirements

Abstract

The adequacy of plant-based diets in developed and developing countries as sources of protein and amino acids for human subjects of all ages is examined. Protein quantity is shown not to be an issue. Digestibility is identified as a problem for some cereals (millet (Panicum miliaceum) and sorghum (Sorghum sp.)) and generally is poorly understood. Direct measurements of biological value in children are reviewed and scoring is considered. Various existing requirement values for amino acids and especially lysine are reviewed, and it is concluded that stable-isotope studies do not yet provide adequate alternative values to N balance data, which for lysine are robust after recalculation and adjustment. A new maintenance requirement pattern is developed, with higher values than those of Food and Agriculture Organization/World Health Organization/United Nations University (1985) but lower values than the Massachusetts Institute of Technology pattern (Young et al. 1989). Calculations of age-related amino acid requirements are based on most recent estimates of human growth and maintenance protein requirements, a tissue amino acid pattern and the new maintenance amino acid pattern. These values appear valid when used to score plant proteins, since they indicate values similar to or less than the biological value measured directly in young children. When used to score plant-based diets in India, no marked deficiencies are identified. All regions score > 1 for adults, whilst for children scores range from > 1, (Tamil Nadhu) from 6 months of age to 0·78 (West Bengal), rising to 0·9 in the 2-5 year old, consistent with reports that high-lysine maize supports similar weight and height growth to that of casein. Inadequate amino acid supply is not an issue with most cereal-based diets. Lysine: Protein scoring: Plant-based diets: ChildrenThe present paper reviews current knowledge relating to protein quality in the context of the meat or wheat debate. The question posed is: are the meat-free or low-meat plantbased diets consumed currently by minorities of vegetarians in the developed world and the majority of populations of the developing world adequate as sources of protein and amino acids for the various age-groups consuming them? The answer to this simple question is in fact difficult to formulate and subject to controversy due to uncertainty about amino acid requirements. The problem was recognized by Food and Agriculture Organization/World Health Organization (FAO/WHO; 1991) in their review of the assessment of protein quality. They recommended that the scoring pattern to be utilized for older children and for adults could be based on values previously adopted for the preschool child, but this recommendation was only made in the absence of agreement on any other suitable values, and was presented as a strict interim measure until a better set of values could be identified.The main reason for this problem is, in my view, because of the unsatisfactory nature of our understanding of N, protein and amino acid homeostasis. In thi...

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