Cooking food may have had important implications in the evolution of the gut microbiome.
Because cooking involves exposing food to heat, it tends to change the various foods' physical and chemical properties.
But do these alterations change the delicate microbial environment of the gut?
That is the question that researchers from the University of California, San Francisco, Harvard University, in Cambridge, MA, and other institutions recently set out to answer.
"Our lab and others have studied how different kinds of diet, such as vegetarian versus meat-based diets, impact the microbiome," says the senior author of the new study, Peter Turnbaugh, Ph.D., an associate professor at the University of California, San Francisco.
"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," he adds.
Cooked foods alter bacterial diversity
In the new study — the findings of which appear in — the researchers started by looking at how different types of cooked and raw food might affect the gut microbiota of mice.
To do so, they fed mice a diet of either raw or cooked beef or raw or cooked sweet potato. The team used these foods, in particular, because had shown that cooking alters their nutritional components and because both commonly feature in human diets.
First, the researchers found, surprisingly, that raw meat and cooked meat did not affect the mice's gut microbiota in obviously different ways. However, there were clear differences between how raw and cooked sweet potatoes affected the gut environment in rodents.
Mice on a raw potato diet had poorer bacterial diversity in the gut, as well as slightly fewer bacteria, compared with baseline measurements. They also had a higher proportion of Bacteroidetes bacteria, which play a key role in the degradation of glycans, a form of sugar.
To confirm these findings, the researchers performed another series of experiments, in which they fed mice not just raw and cooked sweet potatoes, but also white potatoes, beets, carrots, corn, and peas — foods with various degrees of starchiness and digestibility.
As before, the researchers found that cooked versus raw potatoes — of both varieties — affected microbial diversity in the gut differently. The same was not true of the other foods.