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Perhaps We are Not What We Eat After All

Wu_garyIt’s no accident that we’re talking a lot about food on here these days. ‘Tis the season, as they say.

Here at Penn Medicine, we’re finding that what we eat has a greater effect on us than we ever thought.

For example, the common thought has always been that a diet high in red meat poses significant risk for cardiovascular disease due to its high content of saturated fat, but research is now showing some evidence that our gut microbiome, the genes and the organisms and bacteria that live in our gastrointestinal tract may also play a role.

Penn’s Gary Wu, MD, associate director of the Center for Molecular Studies in Digestive and Liver Disease at Penn and director and chair of the Scientific Advisory Board for the American Gastroenterological Association Center for Gut Microbiome Research and Education, is seeing growing evidence that our diet impacts both the structure and function of the gut microbiota that, in turn, influences the body in fundamental ways.

He and his colleagues are looking deeper at how the gut microbiome, which breaks down food and supplies us with the extracted energy and nutrients, is effected by diet and how it can be modified to help the body fight certain diseases and maintain health.  

When we eat, our food starts to break down the minute it interacts with the saliva in our mouth. It then travels through the esophagus and empties into the stomach where acids and enzymes are introduced that serve to further break down food into a mushy paste called chyme. It then passes to the small intestine where it mixes with secretions from the pancreas and bile acids from the liver that help with the absorption of fat. Most nutrients (proteins, fats and sugars) are absorbed along the small intestinal tract as a result of this digestive process. Fiber and other plant-based nutrients that our bodies can’t absorb empty into the colon where they may be metabolized by the gut microbiota into small molecules that we absorb.

Researchers are starting to see that such bacterial metabolites may be linked to certain diseases. A metabolite produced by the gut microbiota from dietary fat and delivered to the liver, for example, could play a role in the development of heart disease.

The gut microbiota can also produce metabolites from our diet that may be beneficial.  For example, it is known that a plant-based, fiber-rich diet may lead to the production of more short chain fatty acids by the gut microbiota which, in turn, may be beneficial by having an anti-inflammatory effect and mitigating the effect of inflammatory diseases such as asthma and IBD.

Wu’s most recent study in the journal Gut also gives some evidence that the construction of the gut microbiome has more to do with where we come from and our genetic makeup than what we eat. Wu and colleagues characterized the diet in 16 healthy omnivores and 15 vegans and found, as expected, that the vegans consumed more carbohydrates, but less animal protein and fat than their omnivore counterparts, but surprisingly only showed slight differences in their gut microbiota.

They also revealed no difference between a plant-based (vegan) diet and omnivores in the production of short-chain fatty acids. This and other evidence led the team to hypothesize that perhaps residence in an agrarian society is associated with a gut microbiota that differs from individuals living in a Western society, which in turn, is necessary for the enhanced production of short chain fatty acids from a plant-based diet. They also believe that differences in gut microbiota related to diet may take several generations to evolve or require very early environmental life exposures that could be independent of diet.

“Although there is a lot of evidence in animal models that the gut microbiota plays a role in disease, we don’t yet know how relevant this is or the impact the gut microbiome has on disease development/risk in humans,” says Wu in summation. “There is a lot that needs to be done to unravel more of the mystery of the significance of the gut microbiome in overall human health.”

Caption: Gary Wu, MD, the Ferdinand G. Weisbrod Professor in Gastroenterology and associate director of the Center for Molecular Studies in Digestive and Liver Disease at the Perelman School of Medicine at the University of Pennsylvania. 


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