Their study, published in The American Journal of Clinical Nutrition, found a diet containing whole grains to positively impact gut bacteria and inflammation as compared to a diet consisting of refined or highly processed grains.
After two weeks following a Western-style diet 81 healthy participants were randomly assigned to a whole grain or refined grain group. Participants received calorie-controlled meals for six consecutive weeks with similar types and servings of fruits, vegetables and protein. The only major difference was one group ate whole grains whereas the other ate refined.
At the end of eight weeks, stool samples taken from the whole grain group showed increased levels of anti-inflammatory microbes and reduced levels of pro-inflammatory microbes unseen in the refined grain group. The anti-inflammatory microbes are known short chain fatty acid (SCFA) producers so it’s no surprise the whole grain group showed modest positive changes in SCFA production.
SCFAs are anti-inflammatory byproducts of bacterial fermentation important for a healthy gut and immune system, and blood samples from the whole grain group were consistent with stronger immune systems.
Beneficial SCFAs form when certain gut microbes feed on (aka ferment) soluble fiber. Interestingly, wheat was the preferred whole grain among participants in the whole grain group, and wheat is high in insoluble fiber, not soluble fiber. Insoluble fiber is known to promote bowel movements, which helps to explain why participants in the whole grain group produced bulkier and more frequent BMs.
Other whole grains, like barley and oats, are better sources of soluble fiber.
Future interventional studies using a variety of whole grains and other foods are needed to better understand their effect on inflammation. Keep in mind most chronic illness, including heart disease, diabetes, cancer and IBD, are associated with ongoing inflammation.
In the meantime, healthy individuals who eat grains should choose whole grains over refined grains when tolerated.
Click here for a full list of whole grains.