Optimization of dietary protein intake during aging.

Abstract

Body protein homeostasis primarily depends on protein intake, even if other dietary factors, such as the energy content of the diet also play a role. However, protein intake can affect protein homeostasis in a variety of ways. First and obviously, the quantity of dietary proteins plays a major role. During short-term adaptation, an increased protein intake results in a temporarily higher nitrogen balance. However, over the long term, nitrogen balance stabilized itself, unless an excess energy intake is associated with the increased protein intake. The amino acid composition is the second classical and important factor. The amount of indispensable amino acids ingested should meet the amino acid requirements. These amino acids will be utilized for protein synthesis, but also as precursors of metabolically active compounds or for regulatory purposes. Digestibility is the other factor affecting the ‘quality’ of dietary proteins. It is classically lower for vegetal than for animal proteins, although recent data show that many plant proteins are highly digestible [1]. The overall quality of a protein can be assessed by global approaches such as the measurement of postprandial nitrogen utilization, using 15N-labeled proteins. More recently a third factor modulating protein retention has been identified. The bioavailability of dietary amino acids over time can be modified by two different means: the pattern of feeding, and the rate of digestion. The influence of the pattern of feeding has been studied for years, for example in the setting of parenteral nutrition. However, it was demonstrated only recently that modifying the repartition of the daily protein intake over a day modulates protein retention [2]. With respect to the influence of the rate of digestion, we recently proposed the concept of ‘slow and fast’ dietary proteins [3] and