Sarcopenia
Protein intake and physical activity are important stimuli for muscle protein synthesis. A number of expert groups have proposed an increase in dietary protein recommendations for older age groups to 1.0-1.2 g/kg body weight per day.
Key nutrient supplementation in older adults is of interest in the prevention of sarcopenia and frailty, since it is a simple, low-cost treatment approach without major side effects.
List of foods by protein content
Below is a list of protein content in foods, organised by food group and given in measurements of grams of protein per 100 grams of food portion. Most natural foods are composed largely of water. The reduction of water content has the greatest effect of increasing protein as a proportion of the overall mass of the foodstuff in question. 
It is to be noted that not all protein is equally digestible. Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method of evaluating the protein quality based on the amino acid requirements of humans.