Obesity and several obesity-related diseases, such as cardiovascular disease and diabetes, are epidemic not only in the United States but around the globe. In addition to their impact on premature death and loss of quality of life, the combined economic burden of obesity and diabetes is nearing one-half trillion dollars in the United States. Furthermore, in many countries, including the United States, there is significant growth in the proportion of the older population, and optimal dietary protein is necessary for healthy aging to minimize age-associated loss of muscle (sarcopenia). Protein is an energy yielding macronutrient, and consumption of protein or any energy yielding macronutrient in excess of need will contribute to unhealthy weight gain. However, some studies have demonstrated that consumption of protein in excess of the Recommended Dietary Allowance for adults (0.8 g/kg body weight/day) is associated with improved health outcomes, including improved body composition and improved insulin sensitivity without detrimental effects on bone or renal function. The effect of higher protein diets on reducing food intake is one mechanism by which protein may influence body composition. In addition to the amount of dietary protein, the quality of that protein can affect health outcomes. Increased consumption of dairy protein, and whey protein in particular, has been associated with decreased body fat without a loss of lean mass. The relatively high branch-chain amino acid concentrations of whey protein may contribute to its physiological effects. Leucine, and perhaps other branched chain amino acids, might mediate changes in body composition through modulation of the mTOR or other key regulatory pathways. With the global public health challenges of obesity and its comorbidities, dietary recommendations to improve health continue to be evaluated. Higher protein diets and high quality proteins can play an important role in improving body composition and supporting healthy aging.