Sweet potatoes are rich in fiber, which research has shown to protect against colon cancer. Dietary fiber is not digested in the small intestine. The fiber makes it to the colon, where it promotes healthy composition of gut microbiota. Antioxidants in purple sweet potatoes stimulate the growth of healthy gut bacteria, including Bifidobacterium and Lactobacillus, two probiotic strains that also play a role in preventing and treating certain infections.
A 2018 study from the University of Illinois shows that walnuts play a key role in keeping the gut in a healthy balance between good and bad bacteria. They are rich in fiber, which the microbiota needs in order to digest food and absorb nutrients. Consuming walnuts increases microbes that produce butyrate, a fatty acid important for colonic health. The nuts also lead to higher levels of Faecalibacterium in the body, which reduces inflammation.