Study: Whole Grains Affect Gut Bacteria, Insulin, and Cholesterol

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AICR recommends choosing whole grains over refined or processed grains— in addition to being higher in nutrients and phytochemicals, whole grains contain more fiber than refined grains. Foods containing fiber protect against colorectal cancer and may keep you full longer, helping you manage your weight. Whole grains are also linked to a lower risbowl full of oats - healthy eating - food and drinkk of heart disease and type 2 diabetes.

Scientists are not sure why whole grains and fiber are beneficial for health, but a new study in mice published in the Journal of Nutrition adds to the evidence that changes in the types of bacteria that live in the intestines—known as the gut microbiota—may be important.

The researchers fed one group of mice flour made from whole grain oats, while the other group of mice got refined flour lower in soluble fiber. Soluble fiber slows the passage of food through the digestive tract, which may help keep you feeling full longer. It is also linked to lower cholesterol and increased insulin sensitivity, important factors in the development of heart disease and type 2 diabetes.

Both diets had the same amount of protein, carbohydrate, fat, and insoluble fiber.

After 8 weeks, researchers found that the mice fed whole grain oat flour had lower blood levels of insulin, hormones associated with insulin resistance, and non-HDL cholesterol—known as “bad” cholesterol. Genes involved in how the liver regulates insulin were also more active.

The researchers were also able to measure the amount and type of bacteria found in the guts of mice in each group. They found that mice fed whole grain oat flour had more of some types of bacteria—including bacteria with known health benefits, such as those in the Lactobacillus genus—and less of other types of bacteria compared to mice fed refined flour.

The study also used statistical analyses to show that differences in the makeup of the gut microbiota appeared to predict most of the differences in blood levels of non-HDL cholesterol and insulin between mice. Scientists have known for awhile that what we eat affects our gut microbiota and while far from conclusive, these analyses suggest that specific changes in the gut microbiota could be behind some of the health benefits of soluble fiber.

Scientists still have a long way to go in understanding the exact mechanism that links fiber and whole grains to better health, but this study is a step forward. In the meantime, the message remains the same—eat plenty of high fiber, plant-based foods like fruits, vegetables, and whole grains for lower cancer risk and better health. Visit AICR’s Foods that Fight Cancer for more information on the research behind whole grains.

This work was supported by General Mills Bell Institute of Health and Nutrition.


    Author: Julia Quam

    Julia Quam, MSPH, RDN, is a registered dietitian nutritionist in the Washington, DC metro area. Julia is passionate about nutrition education and communicating evidence-based information about nutrition and physical activity to improve public health.

    3 thoughts on “Study: Whole Grains Affect Gut Bacteria, Insulin, and Cholesterol”

    1. I am doing a report in my health class and i chose to look into the differences between refined grains and whole grains so this article has helped me a lot to see that whole grains have better health benefits then refined grains.

    2. What was the refined flour made of? That is what may have made the difference. If the refined flour was we as opposed to the whole grain oats than it could have been just the fact that we eat has some very strong anti nutrients that affect gut bacteria and had nothing to do with whether it was whole grains refined grains

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