Cooked versus Raw

 Mice fed cooked sweet potatoes had different microbiome compositions from those fed raw sweet potatoes.

Rachel Carmody

Cooking breaks down the tough, structural molecules of food, making it easier to digest and allowing us to extract more calories from it. A recent study has found that cooked food also alters our gastrointestinal microbiome, the sprawling community of bacteria that live in our guts and influence our overall health and well-being.

Evolutionary biologist Rachel Carmody, at Harvard University, Peter Turnbaugh, an associate professor of microbiology and immunology at the University of California San Francisco, and a research team of colleagues at the two schools, examined the microbiomes of mice fed raw or cooked meat, as well as raw or cooked sweet potatoes. Prior research with meat and tubers had already shown that cooking changed the profile of the foods’ nutrients and other relevant, bioactive compounds. Contrary to the researchers’ expectations, a diet of raw versus cooked meat did not result in meaningful microbiome alterations in the mice. Mice fed raw versus cooked sweet potatoes, however, showed differences in their microbiome composition after just one day. Further experimentation with cooked and raw vegetables, including white potato, corn, peas, carrots, and beets, showed similar effects. The microbes’ gene activity patterns also changed in response to cooking: mice fed cooked sweet potatoes showed reduced expression of genes that help metabolize starch and sugar, presumably because cooking did some of the work breaking down those compounds.

The researchers then sought to gauge how cooking alters human microbiomes. They fed human study participants raw or cooked meals for three days, with stool samples submitted each day. The bacteria contained in stool, a reflection of a person’s microbiome, showed significant alterations based on what the participants ate. However, the alterations were different from those evidenced in mice, and their overall effect on health is not yet understood.

The findings indicate that the celebrated human art of cooking perhaps had a bigger impact on our evolution and our modern states of health than previously thought. “Cooking has shaped the human body over time,” said lead author Carmody. “Like most scientific research, our study has raised more questions that it has answered.” (Nature Microbiology)