Antioxidant-rich diet improved insulin resistance

The Endocrine Society 92nd Annual Meeting

SAN DIEGO — An antioxidant-rich diet improved insulin sensitivity in insulin-resistant obese adults and further enhanced the effects of metformin in a small, preliminary study.

The study included just 29 people, but “results were so striking that we decided to present it immediately,” Antonio Mancini, MD, an endocrinology researcher at Catholic University of the Sacred Heart, Rome, said at a press conference today.

Mancini and his colleagues studied the effects of dietary antioxidants on insulin resistance. The study included 16 men and 13 women aged 18 to 66 years who were obese (mean BMI, 36) and insulin-resistant, but did not yet have diabetes.

The researchers randomly assigned participants to four treatment groups. All groups ate a low-calorie, Mediterranean-type diet averaging 1,500 calories per day, containing only 25% from proteins and the rest from low-glycemic-index carbohydrates. The four groups were:

Low-calorie diet only.
Low-calorie diet plus metformin 1,000 mg.
Antioxidant-rich diet only, with 800 mg to 1,000 mg per day from fruits and vegetables.
Antioxidant-rich diet plus metformin 1,000 mg.

Researchers performed an oral glucose tolerance test and evaluated total, LDL and HDL cholesterol, triglycerides, uric acid and albumin before and after 3 months of treatment.

Despite similar weight loss in all four groups, the two groups who ate an antioxidant-rich diet experienced significant decreases in insulin resistance.

“The most striking results were in [the group assigned to the antioxidant-rich diet plus metformin], with a very big and significant decrease in HOMA-IR, BMI, insulin peak and insulin area under the curve,” Mancini said.

The researchers observed no differences in glucose area under the curve (AUC), lipid metabolism or LAG values.

No adverse events were observed with the antioxidant diet, according to Mancini.

“These data suggest that dietary antioxidants ameliorate insulin-sensitivity in obese subjects with insulin resistance, enhancing the effect of insulin-sensitizing drugs, although the molecular mechanisms still remain to be elucidated,” the researchers wrote in the abstract.

“These are very preliminary data,” Mancini said, adding that the researchers plan to extend the number of people enrolled in the study. – by Katie Kalvaitis

This is an early study, but there is a lot of information out in the environment about what we should eat. The message that fruits and vegetables have health benefits on insulin sensitivity is good. This is just one study, but there are other studies being presented here at this meeting that made interventions in changing the glucose and fructose in the diet and looked at the effects on insulin sensitivity.

– Daniel Bessesen, MD

Professor of Medicine, University of Colorado,
Chief of Endocrinology, Denver Health Medical Center

For more information:

Mancini A. P3-42B. Presented at: The Endocrine Society 92nd Annual Meeting and Expo; June 19-22, 2010; San Diego.