Dietary proteins are necessary for growth, maintenance and repair of the body. The basic protein requirements for maintenance in healthy populations are fairly well understood. However, age and illness may alter protein needs. Protein sources can be selected to better suit the needs of these populations to promote health. The structure of some proteins common in animal feedstuffs (e.g., animal byproducts) renders the proteins less readily bioavailable, but proteins can be modified to increase their utilization. The rate of dietary protein utilization by tissues, especially in the periphery, is linked to bioavailability at digestion, efficacy of amino acid signaling, and presence in the plasma for incorporation into tissues. There may be some advantages of providing proteins with different rates of absorption while optimizing the amino acid profile to deliver targeted benefits.