Diet, Insulin Sensitivity, and Postprandial Metabolism

In a 16-week trial, overweight adults will be randomly assigned to two groups. Changes in
beta-cell function will be the primary outcome. Changes in insulin sensitivity will be the
secondary outcome. Changes in postprandial metabolism, and body weight will be the tertiary
outcomes.

The Diet Group will be asked to follow a low-fat, vegan diet and will receive weekly classes
and support.

The Control Group will be asked to follow a conventional control diet..

This study conducts a pilot substudy to test the hypothesis that changes in insulin
sensitivity and beta-cell function observed in response to a diet intervention correlate with
changes in intramyocellular and/or intrahepatocellular lipid. Another sub-study assesses the
association between metabolic outcomes and gut microbiome. One additional sub-study is
looking for associations between metabolic outcomes and endothelial function.

Inclusion Criteria:

- Men and women age ≥18 years of age

- Body mass index 28-40 kg/m2

Exclusion Criteria:

1. Diabetes mellitus, type 1 or 2, history of diabetes mellitus or of any endocrine
condition that would affect body weight, such as thyroid disease, pituitary
abnormality, or Cushing's syndrome

2. Smoking during the past six months

3. Alcohol consumption of more than 2 drinks per day or the equivalent, episodic
increased drinking (e.g., more than 2 drinks per day on weekends), or a history of
alcohol abuse or dependency followed by any current use

4. Use of recreational drugs in the past 6 months

5. Use within the preceding six months of medications that affect appetite or body
weight, such as estrogens or other hormones, thyroid medications, systemic steroids,
antidepressants (tricyclics, MAOIs, SSRIs), antipsychotics, lithium, anticonvulsants,
appetite suppressants or other weight-loss drugs, herbs for weight loss or mood, St.
John's wort, ephedra, beta blockers

6. Pregnancy or intention to become pregnant during the study period

7. Unstable medical or psychiatric illness

8. Evidence of an eating disorder

9. Likely to be disruptive in group sessions

10. Already following a low-fat, vegan diet

11. Lack of English fluency

12. Inability to maintain current medication regimen

13. Inability or unwillingness to participate in all components of the study

14. Intention to follow another weight-loss method during the trial