The most recent meta-analysis of human protein needs [Rand RM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. Am J Clin Nutr 77 (2003) 109] confirms the conclusions of earlier studies used to establish the RDA (Recommended Dietary Allowance) guidelines in 1989. Therefore, the DRIs (Dietary Reference Intakes) continue to use 0.8 g protein / kg body weight per day as the recommendation. However, the Rand paper (see above) does not distinguish between protein quality in the diet. Rather, it pools together many studies, some of which distinguish between protein quality and others that do not. The result is that the protein recommendation is likely low for those who obtain their protein mostly from plants. The below quotes are from the text of the DRIs:
The Rand paper does not distinguish between types of protein but protein type DOES MATTER:
"In the published meta-analysis of nitrogen balance studies by Rand and coworkers (2003), there were no significant differences in the intakes of dietary nitrogen required to meet nitrogen equilibrium between those studies that supplied dietary protein predominantly from animal, vegetable, or mixed protein sources. It is important to realize however, that this aggregate analysis does not suggest that dietary protein quality is of no importance in adult protein nutrition. The examined and aggregated studies included an analysis of those that were designed to compare good quality soy protein (Istfan et al., 1983; Young et al., 1984) as well as one that involved comparison of whole-wheat proteins (Young et al., 1975a) with animal proteins sources using parallel experimental diet groups. The results of these studies showed clearly that the quality of well-processed soy proteins was equivalent to animal protein in the adults evaluated (which would be predicted from the amino acid reference pattern in Table 10-26), while wheat proteins were used with significantly lower efficiency than the animal protein (beef) (again this would be predicted from the procedure above). Similar studies compared rice and egg proteins (Inoue et al., 1973), wheat gluten and egg proteins (Yanez et al., 1982), and lupin and egg proteins (Egana et al., 1992), all demonstrating the higher quality of the animal protein reference sources. Thus, the aggregate analyses of all available studies analyzed by Rand and coworkers (2003) obscured these results and illustrate the conservative nature of their meta-analysis of the primary nitrogen balance."
The DRIs do not discuss how much MORE protein one would need to consume if most of your protein came from animal sources, plants, legumes, grains or a combination of legumes and grains ("complementary proteins"), but studies with soy suggest an increased need of 0-10% protein above what a person needs that eats animal-derived protein sources. This implies an additional need beyond that amount when protein is derived from plants other than soy. Perhaps that would amount to a additional 10 or 20% beyond the needs of someone eating soy, but an exact number for this can not be derived from published research at this time.
To read the DRI text on this topic CLICK HERE.
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