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Diet switch sparks gut bug revolution in just 24 hours

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IT TAKES just 24 hours to change the balance of microbes in your gut.

Switching to a diet based exclusively on animals or plants triggers rapid changes to the microbes that rule your gut. This knowledge could help fine-tune diets to improve health, as well as reduce the risk of illnesses like inflammatory bowel disease.

The human body contains a community of other organisms known as a microbiome. These microbial cells outnumber our own by 10 to 1, with most of them colonizing the gut. Changing diet can rapidly alter these microbes in mice.

To investigate whether the same was true for humans, Peter Turnbaugh at Harvard University and his colleagues asked 10 volunteers, including one vegetarian, to switch from their normal diet to either a diet based on meat, eggs and cheese, or one rich in grains, fruit and vegetables for five days. Each day the team sequenced the microbial RNA in the volunteers’ feces to identify which gut microbes were present.

“Particularly in the case of the animal-based diet, we saw quite dramatic changes in the abundance of different microbes – even over the course of a single day,” says Turnbaugh. For example, numbers of the bacterium Bilophila wadsworthia increased when people ate the animal-based diet. This organism feeds on bile acids, which aid the digestion of saturated fats in milk. An increase in B. wadsworthia has been linked to inflammatory bowel disease in mice.

Switching to a plant-based diet prompted a hike in the numbers of bacteria that produce a fatty acid called butyrate, which seems to reduce inflammation.

During the plant-based diet, microbes got more of their energy from fermenting carbohydrates, whereas during the animal-based diet the gut inhabitants got more of their energy from breaking down proteins. This ability to switch probably helps the human hosts break down food after a dietary transition (Nature, DOI: 10.1038/nature12820).

Although the results suggest that the animal-based diet may shape gut microbes for the worse, it’s too soon to say which particular diets are optimal for health, says Turnbaugh.

However, it seems likely that changes in our gut microbiota and their metabolic products are important in explaining the influence of diet on many aspects of health, says Harry Flint at the University of Aberdeen, UK. For example, butyrate is thought to reduce colorectal cancer risk by boosting the health of cells lining the intestines and prompting cancerous cells to self-destruct.

Despite the upheaval, the changes to the gut microbiomes were short-lived – they reverted to their original structure about two days after people went back to their normal diets.

This begs the question: is it possible to permanently alter our microbiome or is it fixed? The above study suggests that it is in fact ‘fixed’ but responds to diet very rapidly. What this really means is that although our innate microbiome might be fixed, we can alter it long-term by changing (and sticking with) different diets.

“It’s interesting to think about whether this flexibility may have been adaptive over the course of evolution,” says Turnbaugh. “If you’re exposed to a new set of foods, it would be advantageous to have a microbiome that can rapidly change and allow us to increase our energy from that food.”

This post originally appeared on New Scientist 

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