Ask the RD
Question: I keep hearing about the “human microbiome” and its importance for health. Could you explain how diet affects bacteria in the intestines?
Answer: You have probably heard that you have more microbes (bacteria, fungi, etc.) in and on your body than you have actual human cells. It is shocking to most people, but when you consider the sheer number of microbes, collectively called the microbiota, you realize they must have an impact on your health.
The standard American diet and other Western industrialized diets, high in animal protein and refined carbohydrates, are associated with significantly different and less diverse populations of gut microbes than diets higher in unrefined foods and plants (Graf et al. 2015; Yatsunenko et al. 2012). Western diets are also associated with higher rates of inflammatory diseases, metabolic syndrome, inflammatory bowel disease and some cancers. A different and less diverse microbiota explains some of the difference in disease rates.
To increase and maintain diversity in our microbiota, we need to feed them. What do they eat? Researchers call it “microbiota-accessible carbohydrate” or MAC (Sonnenburg & Sonnenburg 2014). Mostly, that means fiber from plants. We nourish our microbiota with fiber or prebiotics from a variety of vegetables, fruit, legumes, whole grains, nuts and seeds, which also provide phytochemicals and essential vitamins and minerals. It has been known for decades that low-fiber diets are associated with diabetes, heart disease and colorectal cancer. Another way to diversify your gut is to eat fermented foods containing live microorganisms. These foods include kimchi, sauerkraut, kefir, yogurt, cheese, kombucha and miso (Marco et al. 2017).
Keep in mind that we still have a lot to learn about the microbiota, and we may never know if there is an optimal distribution of gut microbes for everyone, much less the foods that create it. Genetics, birth, childhood diet, medications and environment also help to determine what lives in your gut.