New research by scientists at UC San Francisco and Harvard University has revealed our microbiome dynamically responds in different ways to the same foods, depending on whether they are consumed cooked or raw. This novel study is the first to investigate how cooking food changes our gut bacterial diversity.
“Our lab and others have studied how different kinds of diet – such as vegetarian versus meat-based diets – impact the microbiome,” explains Peter Turnbaugh, senior author on the new research. “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.”
The new research began by studying the effect of cooked vs raw foods on the microbiome of mice. Lean beef and sweet potatoes were the initial foods of focus and interestingly, little effect was seen on the animal’s microbiome between cooked and raw meat. Sweet potatoes, on the other hand, provided dramatically different results, with significant changes noted in microbiome responses comparing cooked and raw food.
Cooked sweet potato unsurprisingly offered the animals greater carbohydrate metabolism, primarily due to the way starch becomes more digestible when heated. However, an unexpected observation was the way uncooked sweet potato seemed to be actively damaging certain gut microbes. It was discovered that certain antimicrobial compounds, generally destroyed by the act of cooking, reached the stomach intact when eaten raw.
“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,” says Turnbaugh. “To me, this really highlights the importance of considering the other components of our diet and how they impact gut bacteria.”
The experiments were repeated with white potato, corn, peas, carrots, and beets. The microbiome effects were different from food to food, with the most notable changes between cooked and raw seen in the most starchy vegetables. Beets and carrots, for example, did not seem to cause as many cooked vs raw microbiome differences compared to sweet potato.
The researchers also conducted a small human study to examine if this raw vs cooked effect could be detected in the human microbiome. A small group of subjects ate comparable raw or cooked menus for three days, offering fecal samples along the way. The human experiment was obviously too short to examine any effect on factors such as weight, but noticeable changes were noted in gut bacteria diversity.
“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,” says Turnbaugh.
The research certainly raises a whole host of unanswered questions, such as which foods should be avoided in raw forms and which offer specific nutritional benefits when cooked. From a microbiome perspective it seems our gut bacteria population has evolved to adapt to a diet of cooked food, suggesting solely eating raw food isn’t necessarily a healthier option.
“We’re very interested in doing larger and longer intervention and observational studies in humans to understand the impact of longer-term dietary changes,” adds Turnbaugh.
The new study was published in the journal Nature Microbiology.