Gut Bacteria Vary with Diet

Extreme diets can alter the microbial makeup of the human GI tract, and change the behavior of those bacteria.

By | December 13, 2013

FLICKR, RPAVICHTen volunteers who agreed to eat a diet entirely provided by microbiologist Harvard Peter Turnbaugh and his colleagues are living proof of the gut microbiome’s lability. After five days, those that ate only animal products had a similar suite of bacteria in their guts, which varied dramatically from the microbiome of those feasting on a high-fiber, plant-only diet. Specifically, while the types of bacteria present remained largely unchanged, the abundances of different types responded to the dietary restrictions, according to a study published this week (December 11) in Nature.

“It’s a landmark study,” Rob Knight, a microbial ecologist at the University of Colorado, Boulder, who was not involved with the work, told ScienceNOW. “It changes our view of how rapidly the microbiome can change.”

In 2009, Turnbaugh’s team had shown a similar effect in mice: a change in diet could affect the murine gut microbiome in a single day, in fact. To see if the results would hold up in people, Turnbaugh, along with Lawrence David from Duke University and their colleagues, fed five volunteers a high-protein diet, with meals of bacon and eggs for breakfast, spareribs and brisket for lunch, and salami and cheese for dinner. This group could also snack on pork rinds and string cheese. The high-fiber group, on the other hand, got fruits, vegetables, grains, and beans. Before, during, and after the diet change, the team collected stool samples from each participant to assess the bacterial composition of their guts, as well as the gene expression activity of those microbes.

Before the week was up, the researchers found noticeable differences in the gut bacteria of the two treatment groups. The meat-eaters harbored more bacteria that are able to tolerate high levels of bile acids, which are secreted by the body to help digest meat. The bacteria isolated from this group also appeared to increase expression of genes involved in breaking down proteins. Plant-eaters, on the other hand, had fewer bile-resisting bacteria and higher expression levels of gene associated with carbohydrate digestion.

“There are interesting evolutionary implications to such a rapid response,” David told National Geographic’s Not Exactly Rocket Science. “The ability for the gut microbiome to quickly react to changes in diet may have conferred an extra layer of nutritional buffering, and provided ancient humans with increased dietary flexibility.”

“The paper has made the next leap in the field,” Mayo Clinic gastroenterologist Purna Kashyap told NPR. Of course, he added, the results will need to be well verified and elaborated upon before any sort of health-care recommendation can be made. “With discovery comes responsibility. Once you make this big finding, it needs to be tested appropriately.”

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Avatar of: Paul Stein

Paul Stein

Posts: 126

December 16, 2013

This study has high relevance to the obesity studies involving the microbiome.  Most likely, with bariatric surgery, the bacteria follow the food, and are changed by how the food is handled by the new body.  That's all.  Sure, weight loss occurs, but not because the new microbiome did it.  They were simply a slave to the new food.

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