Protein Complementation of Plant-based Diets.

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:

• 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
• 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.

Inclusion criteria

• 1) Young Adults:
• Adults, age 18 - 39 yrs, Healthy with no known clinical condition which would affect protein or AA metabolism, ex. Diabetes, Stable Body Weight (no more than 5 lb weight loss or gain in the past 3 months)
• Not on any medications that could affect protein or amino acid metabolism e.g. steroids.
• Fasting blood glucose, hemoglobin A1C (HbA1c), urea and creatinine within normal ranges for age.

• Older Adults:
• Adults, aged 60-69 and 70-79 years, Healthy with no known clinical condition which would affect protein or AA metabolism, ex. Diabetes, Stable Body Weight (no more than 5 lb weight loss or gain in the past 3 months)
• Not on any medications that could affect protein or amino acid metabolism e.g. steroids,
• Fasting blood glucose, hemoglobin A1C (HbA1c), urea and creatinine within normal ranges for age.

Exclusion criteria

• Unwillingness to participate or unable to tolerate the diet
• Recent history of weight loss within the last 3 months or on a weight reducing diet Inability to tolerate study diets (ex. Allergy to ingredients).
• Significant caffeine consumption (>2 cups per day)
• Significant alcohol consumption (>1 drink per day i.e. 1 beer or ½ glass of wine).
• Fasting blood glucose, hemoglobin A1C (HbA1c), urea and creatinine outside of normal ranges for age.
• On medications known to affect protein and AA metabolism, renal failure, liver disease, unable to ambulate independently.