Whole grains provide a host of potential benefits, from reduced risk of diabetes and heart disease to improved digestive health and appetite control. Now two clinical trials from Tufts University, published recently in the American Journal of Clinical Nutrition, have shown that substituting whole grains for refined grains, even for a short period, leads to “modest” improvements in the balance of microbes in the intestines (gut microbiome) along with improvements in aspects of the immune response and energy metabolism.
Both studies involved the same 81 healthy adults (ages 40 to 65), half of whom consumed a diet rich in whole grains (whole wheat, oats, and brown rice) for six weeks, while the rest ate refined grains. Other than the different forms of grains, the diets were virtually the same. All foods were provided in order to ensure that the diets kept body weight stable; participants were weighed three times a week and their diets were adjusted if they gained or lost weight. The whole grains provided about twice as much fiber (mostly insoluble fiber) as well as some extra nutrients and other potentially beneficial compounds.
- Happier microbiome. In the first study, researchers assessed the effect of whole grains on the microbiome by analyzing the participants’ stool for its bacterial content and concentration of fats. Previous research has shown that whole grains increase the variety of the microbiome and boost production of short-chain fatty acids, both of which are linked to immune function and digestive health. Along these lines, the whole-grain group in the new study had an increase in bacteria that produce short-chain fatty acids and a decrease in pro-inflammatory bacteria, among other positive changes, compared to those eating refined grains. What’s more, blood samples from the whole-grain group showed small improvements in several markers of a healthy immune response.
- Negating calories. The second study focused on changes in energy metabolism that could affect weight regulation. It found that whole grain consumption led to decreased calorie retention during digestion (as measured by calories in stool) and slightly higher resting metabolic rate—resulting in a net daily energy loss of 92 calories per day, on average, compared to the refined-grain diet. Self-reported hunger and fullness were not statistically different between the two groups. The additional fecal energy losses were due to the extra fiber’s effect on the digestion of other food calories, the researchers suggested.
The Dietary Guidelines for Americans recommend that at least half of your daily grain intake be whole grains. That means at least three servings if you eat a 2,000-calorie-a-day diet; a serving is one slice of whole-wheat bread or half a cup of oatmeal or brown rice, for example.
Also see 5 Things to Know About Whole Grains.