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The consumption of different protein sources and its effect on protein metabolism has been assessed in older women [60]. One diet was composed half of animal proteins and half of vegetable proteins, whereas one‐third of the proteins consumed in a second diet were from vegetable and two‐thirds from animals, and inversely in a third diet. Nitrogen balance was not modified in this study, but whole body protein breakdown was not inhibited to the same extent by the meal when the protein source was from vegetables in comparison with meat [60]. This study showed that intake of high‐quality proteins may be an important issue in older people, suggesting also that aging may be associated with more specific amino acid requirements especially for the EAAs. The quality of dietary proteins and its impact on muscle protein synthesis may be less important when protein intake is sufficient. In a previous study, we compared milk and soy proteins were compared for their potential impact on muscle protein synthesis using a classical steady‐state approach [61]. No differences could be found between the different sources of dietary proteins despite changes in leg amino acid uptakes. However, there is not enough data in the field of aging regarding the issue of EAAs especially at low protein intakes.

Several studies have evaluated the effect of consuming plant‐based proteins on muscle protein metabolism in young, adult, and old rats, pigs, and humans, compared to animal proteins, i.e., meat, milk, and its constitutive proteins (casein and whey proteins) [62]. A few of these studies have focused on the impact of plant‐based foods [60], soy protein [63, 64], or wheat protein [65] ingestion on protein synthesis at the whole body or skeletal muscle level in older individuals. The majority of these studies have reported that good‐quality animal proteins have a greater ability to enhance muscle protein synthesis rate and to support muscle mass than plant‐based proteins. Therefore, although plant‐based protein sources that are rich in fiber and micronutrients may be valuable to improve nutritional density of diet, they have lower anabolic potential than animal‐based proteins. Strategies to improve these properties by increasing protein quality (i.e., their amino acid composition and digestibility) including selective breeding, fortifying plant‐based proteins with specific EAAs, mixing several plant proteins, and mixing plant‐ with animal‐based protein sources can support a healthier life, notably to prevent chronic disease, such as sarcopenia, in aging.