Human nutrition
The protein requirement for each individual differs, as do opinions about whether and to what extent physically active people require more protein. The 2005 Recommended Dietary Allowances (RDA), aimed at the general healthy adult population, provide for an intake of 0.8 grams of protein per kilogram of body weight. A review panel stating that "no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise."
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.