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close this bookEnergy and Protein Requirements, Proceedings of an IDECG workshop, November 1994, London, UK, Supplement of the European Journal of Clinical Nutrition (International Dietary Energy Consultative Group - IDECG, 1994, 198 pages)
close this folderProtein requirements of infants and children
View the document(introductory text...)
View the document1. Introduction
View the document2. Protein requirements of infants
View the document3. Protein requirements of children and adolescents
View the document4. Protein needs during catch-up growth
View the document5. protein needs associated with infection
View the document6. Assessment of protein quality of weaning diets
View the document7. Future research needs
View the documentReferences
View the documentDiscussion
View the documentReferences

6. Assessment of protein quality of weaning diets

The procedures for making adjustments for protein digestibility and quality were described thoroughly in the 1985 report and in a subsequent Joint FAO/WHO expert report (Joint FAO/WHO Expert Consultation on Protein Quality Evaluation, 1991) and do not need to be reiterated here. Use of the protein digestibility corrected amino acid score is considered the most appropriate method for evaluating protein quality. This method obviously depends heavily on the estimated amino acid requirements at each age. For infants, both the 1985 report and the 1991 Consultation recommended that the amino acid composition of human milk be accepted as the suggested pattern of requirement. However, as the discussion in section 2.5 indicates, the essential amino acid content of human milk is generally above 'requirements' based on calculated needs for growth and maintenance. Thus, using the human milk amino acid pattern (mg/g protein) as the basis for evaluating weaning foods may underestimate their protein quality (depending on which amino acids are potentially limiting in the food being evaluated).

For children, the 1991 Consultation (FAO/WHO Expert Consultation, 1991) recommended that the amino acid scoring pattern for preschool children (see section 3.4) be used for all age groups (except infants). Until more information is available on amino acid requirements, this recommendation appears to be justified. However, because that scoring pattern was based on only one set of studies in a small sample of children, replication of the findings is essential. The lack of information on sulfur amino acid needs is particularly unfortunate as these amino acids, together with Lysine, may be marginal in vegetable protein sources if Rose's (1957) 'safe' rather than 'minimal' level is closer to true needs (see section 2.5). Even so, data from Guatemala (Scrimshaw et al, 1961; Torun and Viteri, 1981b; Torun et al, 1984) suggest that predominantly vegetable multi mixes can provide an adequate source of amino acids for children beyond the age of one year.

Aside from protein quality, any evaluation of weaning foods must also consider the content and bioavailability of other nutrients, particularly trace elements, and the potential presence of 'antinutritional' factors such as plant lectins.