The researchers randomly assigned the subjects to one of four treatment groups. All groups ate a low-calorie, Mediterranean-type diet averaging 1,500 calories daily, containing only 25 percent from protein foods, with the rest made up of low-glycemic-index carbohydrates (carbs that do not raise blood sugar levels quickly or greatly, such as whole grains). Group A only ate this kind of diet, and group B ate the same diet plus took the drug metformin. For groups C and D, the researchers prescribed a diet enriched in antioxidant, with a calculated intake, 800 to 1,000 milligrams a day, coming from fruits and vegetables, but group D also took metformin.

Despite similar weight loss in all the groups, only the two groups receiving the antioxidant diet (groups C and D) had a significant decrease in insulin resistance, the authors reported. Group D had the best improvement in insulin resistance on some measures of insulin response to an oral glucose tolerance test, according to the abstract.

Subjects reported no adverse effects from the antioxidant diet, Mancini said. When asked about the risk of adding more antioxidants to a diet, he stated, "We think that a total antioxidant level of 800 to 1,000 milligrams a day is safe and probably not close to the maximum tolerable level."

SOURCE The Endocrine Society