Antioxidants in Diet Can Improve Insulin Sensitivity: New Study

Preliminary research from Italy indicates that regularly eating foods that are rich in antioxidants (substances that help protect cells from oxidative damage) can improve insulin sensitivity and enhance the effects of the diabetes drug metformin in obese adults with insulin resistance. Insulin resistance, a condition in which the body requires extra insulin to maintain normal blood glucose levels, is a hallmark of Type 2 diabetes.


The study, presented at the Endocrine Society’s 92nd Annual Meeting, looked at 16 men and 13 women, ages 18 to 66, who were obese and insulin resistant but who did not have diabetes. The participants were randomly assigned to one of four treatment groups. Group A followed a Mediterranean-style diet with roughly 1,500 calories daily composed of about 25% protein and 75% low-glycemic-index carbohydrates; Group B followed the same diet but also took metformin; Group C followed the Mediterranean-type diet supplemented with 800–1,000 milligrams per day of antioxidants provided by fruits and vegetables; and Group D followed the antioxidant-supplemented meal plan and also took metformin.

On average, all the groups lost similar amounts of weight. However, only people in the two groups receiving supplemental antioxidants from fruits and vegetables showed a significant decrease in insulin resistance. Those in the group receiving both antioxidants and metformin showed the greatest improvement in insulin resistance based on their response to an oral glucose tolerance test.

According to lead study author Antonio Mancini, MD, “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… 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.”

Mancini and his team note that further study is required to explain the mechanisms behind the antioxidants’ apparent improvement of insulin sensitivity.

For more information, read the article “Well-Defined Quantity of Antioxidants in Diet Can Improve Insulin Resistance, Study Finds.” And to learn more about antioxidants, see the article “Antioxidants: Should You Supplement?”

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  • calgarydiabetic

    This is funny because I remember reading a study where anti-oxidant supplements were found to increase insulin resistance.

  • Nicky (Type 2)

    I notice that these were DIETARY antioxidants, not supplements.

  • still too fat

    Any nutritional substance absorbed by the digestive tract is “dietary,” whether it be fresh food, processed food, or in pill form.

  • Thomas

    Information is constantly coming out concerning insulin resistance. Some say this will help and there others that will say their plan works. I have decided to ignor all of them and go with the insulin pump and stay on a low glycemic diet and count my carbs before I eat.

  • Jerry

    The more I read about all these “studies” the more confused I become. I will just try to eat plenty of veggies and fruit and keep on taking Glipizide, Metformin and Actos. Even on that diet I find it hard to lose weight.

  • Classic

    I’m type 2, 6’1″, large framed and lost 65# (down to 175). Keeping my carb intake below 50g per day and taking 70u of Lantos and between 30u-54u of Apeidra each day and my numbers still run anywhere from 275 – 350. I’m beginning to believe that non of the doctors or researchers know a hill of beans about how to treat/attack insulin resistance.

  • Laurie phillips

    I rotate between the diet and the flat belly or diabetic cookbook diet and haven’t lost but 5 lbs. I have seen my sugar readings go up due to menapose these last few months.
    I am wondering if lowering my carbos would be beneficial since most of the diets I am on have me at 167 to 198 carb’s this is with Metformin 2 to 3 x a day. Due to my work load as a housekeeper cleaning two to three homes I don’t know if my body can handle a lower carb intake.

  • Sandra Winkler

    We diabetics are on a medical merry go around. Why don’t we focus on the cause instead of treating symptoms? Not everyone has diabetes because of genetics.There are 100,000 million diabetics in the world. Mine came from stress. Read what Dr.Hyman’s websight says. I think he is the only doctor who is on the right track.Pharma-
    seutical companies are taking in billions by pushing drugs.The body systems are messed up from lifestyle, processed food, and stress.I am on insulin which eventually damages the heart.We need functional medicine to help us treat the cause.

  • Bonnie Copeland

    That all sound great hope they can figure something out. Why are we so insulin resistant? After 17 yrs of being a type 1 diabetic I finally seen a nutritionist and I do not have a cure yet, but I have found some hope. It’s all the fat in our diets. You try to eat low carb and end up eating higher fat, all fat free products have higher carbs they got to put something in there to make it taste good. So I have been trying to have the best control with shots and nothing seemed to be working, started counting the fat no more than 10 per meal and now the insulin I take when I count the carbs actually works. Amazing wish someone would have told me that a long time ago!

  • Millie

    It doesn’t make sensde to me! If I eat an orange my gut will absorb the vit C plus other vitamins, micronutrients, liquids, fiber and all of those miraculous substances that can be created only by nature.
    If I take a Vit C supplement, I’ll absord the chemical components used to make the pill or capsule, and the chemical equivalent of the Vit C, flavorings and preservatives.
    So, no,food and pills are not both “dietary ” in any sense of the word.

  • Angela Norton

    Oh boy, such a lot of passionate missunderstanding! I believe and try to practice a healthy diet (the verdict is still out on that one but fresh produce and minimally processed food), a varied diet, and a balance of food intake and excercise.
    To Classic: my heart goes out to you. You don’t seem overweight, so stress may have something to do with your resistance, however you are taking much less Apidra (bolus insulin) than Lantus (basal). You may need to increase your Apidra. Your levels are so high, you may have glucose toxicity, which needs a lot of insulin to normalize before there is a reduction in the need. Fasting blood glucose (BG) is your Lantus dose, get that right first; then turn to your daytime BG’s and insulin.
    To Sandra: Insulin does not cause heart problems! Even those without diabetes take insulin. It is an important hormone without which we die. Type 2’s may produce some insulin, but Type 1’s do not.
    Prolonged high blood sugar is the cause of many forms of heart disease – hence the #1 cuase of death to diabetics.
    And Millie: I agree 100%, just make sure you wash off all the gunk sprayed on the produce without a skin to peel.
    To the author: I do not think any one single nutrient is a fix for anything. Life would be to easy and it’s not. Too much of anything, except happiness, is not good for you.

  • Alex Rounds

    Seems to me that a sample of 29 people divided into four groups is not a large enough sample to extract significant and usable conclusions. The study hints on a possible link between antioxidants with metformin and blood-glucose levels. The results offer direction to other researchers for possible confirmation, but to draw conclusions from such a small study is not appropriate.

    My wife notes that we likely need to increase our intake of chocolate because she just read a report that includes it along with fish, fruits, etc, as a source of antioxidants. Or maybe that’s just wishful thinking?

  • gys de Jongh

    some of it proved to be a hype, to little antioxidants may not be a good idea either…

    Vitamins C and E and beta carotene supplementation and cancer risk: a randomized controlled trial.
    CONCLUSIONS: Supplementation with vitamin C, vitamin E, or beta carotene offers no overall benefits in the primary prevention of total cancer incidence or cancer mortality.
    PMID: 19116389

    Antioxidant supplements for preventing gastrointestinal cancers.
    CONCLUSIONS: We could not find convincing evidence that antioxidant supplements prevent gastrointestinal cancers. On the contrary, antioxidant supplements seem to increase overall mortality. The potential cancer preventive effect of selenium should be tested in adequately conducted randomised trials.
    PMID: 18677777

    How increased oxidative stress promotes longevity and metabolic health: The concept of mitochondrial hormesis (mitohormesis).
    In summary, the findings discussed in this review indicate that ROS are essential signaling molecules which are required to promote health and longevity.
    PMID: 20350594

    Antioxidants prevent health-promoting effects of physical exercise in humans.
    exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.
    PMID: 19433800

  • virginia wolfe

    I am not on any medication as my doctor wants me to control this and loose weight also.I do ok with my numbers, but I eat the same thing day in and day out. Now I am sure I will get tired of eating the same food, that is something I will talk to my doctor about. ginny wolfe

  • Judy Moses

    Why don’t we just get to the hormone malfunction issue?

  • Mike

    Has anybody seen this “soy beverage enriched with bioactive pepitdes lowers fasting blood glucose and HbA1c in type 2 diabetic patients with inadequate glycemic control”. This was presented at ADA meetings in Orlando, Florida.

    This looks very promising but I would like someone with the knowledge to comment on this.

  • Mrs. Eat Well

    Fact is there are multiple reasons for dysregulation of glucose and insulin resistance as well as diabetes. Some diabetics (typically child) are due to virus that attacked the beta cells. But it’s true most are suffering due to toxic over load and genetic mitochondrial dysfunction. You’re metabolic imbalance is causing the disruption in your insulin secretion and sensitivity. Much of the degredation of type 2 into type 1 diabetes is chronic poor genetic signaling based on poor lifestyle choices as well as or because of genetic mutations. Genetic mutations create an environment that leaves certain people more susceptible to toxic overload and metabolic imbalance. These people need to pay even more attention to healthful whole food eating of low glycemic foods and many times require more fats and protein, but not all. Some simply do better with higher fiber foods at more consistent eating patterns. Oxidation or ROS is only part of the puzzle. Treating or supporting insulin secretion and metabolism is about exercise, appropriate food intake, antioxidant support, genetic pathway support and decreasing toxins. It’s not as simple as just eating more veggies, though it helps a lot!! Imbalance leads to more oxidation and destruction of DNA and cellular activity. Diabetes ceates high ROS and inflammatory signals. Which came first? Who knows.

  • Lieena

    Has anyone ever used Alpha Lopoic Acid..I have been reading about it and have been using it for about 6 days now..I have pre-diabetes..I will have a blood test this week, it may be to soon to see a difference..but I sure do feel good…I take a 600 mg capsule once daily..