Human gut bacteria seem to be picky eaters

People who eat a diet high in fats and animal protein tend to have a different group of bacteria flourishing in their gut compared with those who eat a mostly plant-based diet, researchers have found.

Researchers suspect that the microbes within us affect our vulnerability to infectious disease and interact with the immune system. The new study was part of the scientific effort to try to understand how bacteria interact with their human hosts. 

Either of two specific types of microbes seem to take over the human gut and dominate, the study in this week's online issue of the journal Science suggests.

Bacteroides prefer the guts of people eating a carnivorous diet high in saturated fat while another type of bacteria, Prevotella thrive on a carbohydrate-based diet. 

In the study, researchers collected stool samples from 98 subjects who also filled in questionnaires about their diet.

Dr. James Lewis of the University of Pennsylvania and his co-authors then used gene sequencing technology to examine the genetic code of bacteria from the participants' colons. That's how they found the two groups of bacteria, known as enterotypes.

In the second part of the experiment, 10 healthy, non-obese Americans stayed in a hospital for 10 days as part of a controlled eating study. Half ate high-fat, low-fiber diet, and the other ate a low-fat, high-fibre diet.

Slight, rapid change in bacteria

The investigators found that although the gut microbial communities changed slightly within 24 hours of the diet switch, peoples' enterotypes stayed largely the same over the 10-day study.

"Changes were significant and rapid, but the magnitude of the changes were modest, and not sufficient to switch individuals between  the enterotype clusters associated with protein/fat and carbohydrates," the study's authors said.

The findings complement those of a recent study that compared the diet of European children who eat a typical Western diet high in animal protein and fat to children in Burkina Faso, who eat a high carbohydrate diet low in animal protein, the researchers said.

In that study, the Bacteroides enterotype dominated in the European samples whereas the African samples were dominated by Prevotella — the same pattern as in the latest study.

Other differences between Europe and Burkino Faso could explain the findings but diet offers "an attractive potential explanation," Lewis and his co-authors said.

Their next step is to determine whether those with the Bacteroides enterotype have a higher incidence of diseases associated with a Western diet, and whether long-term diet changes can lead to a lasting switch to the Prevotella enterotype.