Protein Complementation of Plant-based Diets.

Overview

Amino acids are the building blocks of proteins which are needed by the body for growth, and bodily functions. If even one amino acid is in short supply, this will negatively affect growth and various functions in the body. Animal foods like meat, fish and chicken contain all the amino acids needed by the body in the correct proportion. These foods are considered high quality protein foods. However plant proteins like lentils, wheat, rice are low in at least one amino acid. This means that plant proteins are considered low quality proteins. Data from the investigators lab and others show that when eating plant foods, combining grains and legumes like rice and beans, peanut butter and bread, (protein complementation) will provide a complete protein which contains all the amino acids needed by the body. However, some maintain that it is not necessary to combine foods like grains and legumes in the same meal as long as all the amino acids are consumed within a 24h period. This has never been tested. The goal of this study is to compare the effects non-complementation to protein complementization on whole body protein metabolism in young and older adults.

Complementation of plant proteins with complementary amino acid profile (cereal grain + legume) in each meal can improve the protein quality of plant based diets. However, some maintain that if a variety of plant foods are consumed throughout the day, all essential amino acids are provided and protein complementation at each meal is unnecessary. This assumption has NEVER been tested, yet it forms the basis of current expert recommendations for vegetarian diets. Evidence from the investigators lab and others demonstrate that there is no storage pool of amino acids in the body; when one amino acid is deficient in the diet for protein synthesis, all others are in relative excess and are oxidized resulting in poor growth and lower rates of protein synthesis. Therefore, current recommendations for plant based diet consumption could be misleading. Skeletal muscle plays an important role in the adaptations of body proteins to nutritional changes and during stress. Therefore, knowledge of skeletal muscle response to changes in dietary protein intake from animal to plant based protein is an important prerequisite to understand the body's capacity, especially in the elderly, to adapt to alterations in dietary protein quality from animal to plant based, whether in complementation or non-complementation fashion. The contribution of skeletal muscle to protein breakdown is calculated by measuring urinary 3-methylhistidine. This amino acid is produced in muscle from post-translational modification of histidine and released from actin and myosin. It is not reutilized for protein synthesis but is excreted in the urine. Therefore, the urinary output of 3-methylhistidine is a quantitative index of daily muscle protein breakdown. Objectives: 1. To assess whole-body protein metabolism (WBPM) (protein synthesis, protein breakdown and protein balance) using a single dose \[15N\]glycine and measuring cumulative excretion of \[15N\]urea in urine in human adult consuming a PB diet provided in a complementary or non-complementary fashion in males and females 18 -39, 60-69 and 70-79 years and 2. To assess the contribution of skeletal muscle to protein breakdown by measuring urinary 3-methyhistidine. Hypothesis: Protein synthesis and balance will be lower, but breakdown will be higher in the non-complementation PB diets compared to omnivorous diet (control) and lacto-vegetarian diet.