Dietary proteins elicit a wide range of metabolic and physiologic functions that are far beyond their traditional role as sources of energy and also indispensable amino acids. Proteins play a significant role in the regulation of appetite, food intake, body weight, and body composition. Their role in regulation of blood pressure, glucose and lipid metabolism, bone metabolism, and immune system is also shown. The role of proteins as the most satiating macronutrient in regulation of food intake, body weight and body composition is well-studied. The direct interaction between dietary proteins and the gastro-intestinal (GI) tract via communication with endogenous satiety signals, in addition to their effects on protein synthesis are major underlying mechanisms. The interaction of proteins with the GI tract can be elucidated by their effect on gastric emptying rate, GI transport and absorption, GI-brain communication via gut-brain axis, and more recently by their effect on gut micro biota. However, there is increasing evidence indicating that these effects are sourcedependent. Physicochemical properties of individual proteins, including digestion kinetics, digestibility, amino acid composition and sequence, bioactive peptides and also non-protein bioactive components conjugated with proteins are potential factors determining their physiologic and metabolic properties. Therefore, the purpose of this review is to examine the most recent findings about the role of the source of protein in regulation of food intake, body weight, and body composition.