Phenylalanine Requirement of Adults >65 Years.

Inclusion Criteria: 1. Healthy elderly males and females \> 65 years 2. Willingness to participate in the study and completed the screening procedures (height, weight, fasting blood sample and medical history questionnaire). 3. No recent history of weight loss 4. Absence of chronic disease or acute illness that could affect protein and AA metabolism (diabetes, cancer, liver or kidney disease, HIV, acute cold or flu, hypo or hyperthyroidism, rheumatoid arthritis treated with anti-inflammatory medications. 5. Non-smoking 6. Willingness to consume the diet provided Exclusion Criteria: 1. Presence of disease known to affect protein and AA metabolism (diabetes, cancer, liver or kidney disease, HIV, acute cold or flu, hypo or hyperthyroidism, rheumatoid arthritis treated with anti-inflammatory medications). 2. On medications known to affect protein and amino acid metabolism (steroids). 3. Recent significant weight loss. 4. Individual on weight reducing diets. 5. Inability to tolerate the diet 6. Unwilling to have blood drawn from a venous access, or using a ventilated hood indirect calorimeter for the purposes of the study. 7. Significant coffee consumption of more than 2 cups/day 8. Significant alcohol consumption of more than one drink/day