The gut microbes we carry are impacted by many factors, including our diet. Now researchers have found that cooked and raw foods have different effects on the microbiome, which is known to have a significant influence on our health. This work can help us understand how a healthy gut microbiome is built and maintained, and potentially how to repair one that’s dysfunctional.
"Our lab and others have studied how different kinds of diet—such as vegetarian versus meat-based diets—impact the microbiome," said senior study author Peter Turnbaugh, Ph.D., an associate professor of microbiology and immunology and a member of the executive leadership of the UCSF Benioff Center for Microbiome Medicine. "We were surprised to discover that no one had studied the fundamental question of how cooking itself alters the composition of the microbial ecosystems in our guts."
This study, reported in Nature Microbiology, split mice into groups that were fed one of four diets - raw or cooked sweet potatoes, or raw or cooked meat. These foods were chosen since previous research has indicated that cooking changes the nutritional content of meat and sweet potatoes.
The researchers found that the influence of meat was basically the same regardless of whether it was cooked or not. In the case of the sweet potatoes, however, the raw version had several different effects than the cooked potatoes; the composition of the microbiomes in the animals, the patterns of microbial gene activity, and the metabolic products that were generated were all affected in different ways. The scientists followed up on these findings with a wide variety of different vegetables, including beets, corn, white potato, peas, and carrots, which confirmed their results.
The investigators suggested that two important factors make the difference. First, the cooked food enables the small intestine of the host to absorb more calories, which leaves less food for microbes living further along in the gut. Second, raw foods are also a source of antimicrobial compounds that can do damage to certain microbes in the gut.
"We were surprised to see that the differences were not only due to changing carbohydrate metabolism but also may be driven by the chemicals found in plants," Turnbaugh noted. "To me, this really highlights the importance of considering the other components of our diet and how they impact gut bacteria."
The scientists followed up on the chemical changes that were triggered by the different diets to learn more about the food-derived compounds that were influencing the microbiome.
The researchers also sought to confirm these findings in humans. Study participants were given a raw diet for three days and a cooked diet for three days. Stool samples showed that human microbiomes are also changed significantly in different ways by the diets.
"It was exciting to see that the impact of cooking we see in rodents is also relevant to humans, although interestingly, the specifics of how the microbiome was affected differed between the two species," Turnbaugh added. "We're very interested in doing larger and longer intervention and observational studies in humans to understand the impact of longer-term dietary changes."