Food as Medicine

Gut Microbiome – Strike It Rich with Whole Grains

BY Michael Greger TIMEMay 18, 2022 PRINT

Yes, we live in a so-called obesogenic environment—cheap junk food everywhere, thanks in part to subsidies going to the “’food industrial complex’ which manufactures obesogenic foods that foster addiction.” The root causes may make obesity difficult to escape. But, look, a lot of people do. If it was just the external environment, why isn’t everyone obese?

Some individuals seem to be more susceptible than others. This suggests a genetic component, supported by studies of twins and adopted kids. But, the genes we’ve identified only account for maybe 6 to 11% of the variation in body mass index between individuals. So, maybe variation in our “other genome” may be playing a role—all the different microbes that inhabit our body. We have a hundred times more bacterial genes inside us than human genes.

What this study found is that people tend to fall into one of two groups: those who have lots of different types of bacteria in their gut (so-called high gut “bacterial richness”), and those with relatively few types. And, those with low bacterial richness had more overall body fat, insulin resistance (the cause of type 2 diabetes), high triglycerides, and higher levels of inflammatory markers, like C-reactive protein, compared to high bacterial richness individuals. And, not only did folks with lower bacterial richness start out heavier, but the obese individuals with lower bacterial richness also gained more weight over time.

The question then becomes: can a dietary intervention have any impact? They tried a calorie-restricted diet, which by definition isn’t very sustainable. But, what we can do is increase our fruit and vegetable intake, which is associated with high bacterial richness. One of “[a] number of studies [that] have associated increased microbial richness, with diets higher in fruits, vegetables, and fiber.”


Now, just giving fiber-type supplements didn’t seem to boost richness. But, the compositional complexity of a whole food—like whole grains—could potentially support a wider scope of bacterial types, thereby leading to an increase in diversity. But, human studies to investigate the effects of whole grains have been neglected—until now.

Folks were given whole grain barley, brown rice, or both, for a month. And, they did cause an increase in bacterial community diversity. Therefore, it may take a broad range of substrates to increase bacterial diversity, and this can be achieved by eating whole plant foods.

And, the alterations of gut bacteria in the study coincided with a drop in systemic inflammation in the body. See, we used to think that the way fiber in whole grains helped us is by gelling in our small intestines right off our stomach, slowing the rate at which sugars were absorbed, blunting the spike in blood sugars one might get from refined carbs. But, now we know the fiber is broken down in our colon by our friendly flora, which release all sorts of beneficial substances into our bloodstream that can have anti-inflammatory effects, as well. So, maybe what’s happening in our large intestine helps explain the protective effects of whole grain foods against type 2 diabetes.

And, interestingly, the combination of both barley and brown rice worked better than either alone—suggesting a synergistic effect. This may help explain “the discrepancy of the health effects of whole grains obtained in [population-based versus] interventional studies.”

Observational studies strongly suggest that those who consume three servings of whole grains a day tend to have a lower body mass index, less belly fat, less tendency to gain weight. But, recent clinical trials, where you, like, randomize people to eat white bread rolls versus whole wheat rolls, failed to provide evidence of a beneficial effect on body weight.

Of course, whole grains are so superior nutritionally that they should continue to be encouraged. But, maybe the “interventional trials… failed to show [weight] benefits because they focused on a limited selection of whole grains, while in [the population studies], subjects are [more] likely to consume a diverse set of whole grains which might have synergistic activities.”

This story was originally published on the site.

Michael Greger, MD, FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. He has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on “The Dr. Oz Show” and “The Colbert Report,” and was invited as an expert witness in defense of Oprah Winfrey at the infamous “meat defamation” trial. This article was originally published on
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