A new study has found that a diet rich in natural antioxidants may improve insulin resistance in obese adults.
"The beneficial effects of antioxidants are known, but we have revealed for the first time one of their biological bases of action—improving hormonal action in obese subjects with the metabolic syndrome," said principal author Antonio Mancini, MD, an endocrinology researcher at Catholic University of the Sacred Heart in Rome.
Antioxidants enhance the effect of the insulin-sensitizing drug metformin, which is beneficial to people who suffer from the syndrome wherein they cannot efficiently use insulin, the hormone that regulates glucose (sugar) in the blood.
Some evidence exists that oxidative stress may play a role in the metabolic syndrome, according to Mancini. Oxidative stress, a biochemical mechanism that can lead to damage to blood particles and to cells, results from an imbalance between an excessive amount of oxidants and decreased antioxidant defenses. Oxidative stress also plays a part in aging.
Antioxidants, which are found naturally in fruits, vegetables, and legumes and nuts, include vitamins E and C, selenium and carotenoids, such as beta-carotene.
In a study that included 16 men and 13 women, ages 18 to 66 years, who were obese and insulin-resistant, but were not yet diabetic, Mancini and his colleagues studied the effects of dietary antioxidants on insulin resistance. The groups were put on a low-calorie, Mediterranean-type diet. 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.
The team found that the group D had the best improvement in insulin resistance on some measures of insulin response to an oral glucose tolerance test.
"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," said Mancini.