Branched-chain amino acids (BCAAs) are essential nutrients that the body obtains from proteins found in food, especially meat, diary products, and legumes. Data from rodent studies suggest that reduction of dietary BCAAs will promote fat mass loss and improved control of blood glucose. The purpose of this study is to test if reduction of dietary BCAAs without reducing calorie intake will lead to similar metabolic benefits in humans. Here the investigators test the feasibility of reducing dietary BCAAs using BCAA-free meal replacement beverages for two months.

This study, which will be completed over three months, involves replacing two meals a day with meal replacement beverages for two months, with a one month follow-up visit. These beverages will be made up by subjects using either a complete protein powder or BCAD2, a BCAA-free medical food. Participants will complete food diaries at baseline and at one month intervals during the study, and compliance will be assessed via food diaries, weekly telephone contact, and measuring returned food powder.

Inclusion Criteria:

1. Male between the age of 35 - 65
2. BMI between 28 - 35 (mildly obese/overweight)
3. Fasting glucose level of 101 - 125 mg/dL
4. Able and willing to give written informed consent
5. Stable weight (within 5 lbs. for at least 3 months)
6. Not taking (or willing to cease taking) over the counter vitamin/mineral supplements
7. Not planning to begin an exercise or diet program

Exclusion Criteria:

1. Female
2. Outside required age range of 35 - 65
3. BMI not within range of 28 - 35
4. Fasting glucose not within range of 101 - 125 mg/dL
5. Use of prescription medications for diabetes or weight-loss
6. Use of and unwillingness to discontinue over the counter supplements (e.g. cinnamon, chromium, protein powders) or weight loss beverage or meal plans (e.g. SlimFast or Jenny Craig).
7. Low baseline albumin or pre-albumin levels (below normal reference range)
8. Significant anemia (Hemoglobin < 11 g/dL)
9. Known bleeding disorder or platelet dysfunction
10. Already eating a low protein diet (less than 14% total caloric intake from protein), as calculated from food diaries provided by subjects
11. Participating in intensive exercise training program (high to moderate intensity exercise greater than 210 minutes per week) or planning to start new exercise program during study period.
12. Significant co-morbidities (including kidney disease, liver disease, GI disease, cardiovascular disease, respiratory disease, malnutrition, substance abuse, psychiatric disease, or a diagnosed eating disorder).
13. Planned smoking cessation or attempt at smoking cessation during study period
14. Inability to tolerate meal replacement beverages due to palatability
15. Recent weight loss (> 5 lbs within 3 months).
16. Bariatric surgery, gastric banding or liposuction
17. Current or past (within 1 year) use of illicit drugs
18. Claustrophobia