Protein’s characteristic ability to promote satiety has made it a point of interest when dealing with weight maintenance. Satiety has been defined and supported by elevated amino acid concentrations, responses of anorexigenic hormones or protein induced energy expenditure. The metabolism of protein (or the process of digestion and rebuilding of tissue in the body) actually expends more energy than seen in the digestion of fat or carbs. During energy deficit (i.e. a weight loss diet), protein is able to keep you full even though less calories are being consumed. Additionally, adequate or high protein intake helps to preserve muscle mass, which can often be lost during weight loss diets.
Source: Soenen et al. Proteins and satiety: Implications for weight management. Curr Opin Clin Nutr Metab Care. 2008; 11: 747-751.