Western diets promote bacterial growth in the small intestine, increase fat digestion and absorption

A researcher at Midwestern University led a new study showing that Western diets, high in fat and simple sugar, promote the growth of bacteria in the small intestine that increase fat digestion and absorption. The goals of the study, published in the journal Cell Host and Microbe on April 11, 2018, were to determine if microbes were required for digestion and absorption of fats, to begin to learn which microbes were involved, and to assess the role of diet-induced microbes on the digestion and uptake of fats.

Kristina Martinez-Guryn, Ph.D., R.D., Assistant Professor of Biomedical Sciences at Midwestern University, led the work on this project in collaboration with senior author, Eugene Chang, M.D., at the University of Chicago. This work involved a series of complicated experiments to demonstrate that mice reared germ-free (GF) are protected from diet-induced obesity and are unable to absorb fat compared to conventionally-raised mice, also known as specific pathogen free (SPF) mice. When the germ-free animals are given small intestine microbiota from high fat conditions, they are able to absorb fat. The findings from this work suggest that these microbes facilitate production and secretion of digestive enzymes into the small bowel. Those digestive enzymes break down dietary fat, enabling the rapid absorption of calorie-dense foods.

Additional experiments were performed to show that bacteria-derived bioactive products stimulate absorptive cells in the small intestine to package and transport fat for absorption. Therefore, bacteria in the small intestine orchestrate a series of events that allow the host to efficiently absorb fat. It is expected that these diet-microbe interactions can lead to over-nutrition and obesity over time.

While most studies have focused on the large intestine, this study highlights the microbiota in the small bowel, the major site of macronutrient digestion and absorption. Understanding host-microbe interactions in this region has significant clinical implications, especially in preventing and treating obesity and diabetes. "I would say the most important takeaway overall is the concept that what we eat--our diet on a daily basis--has a profound impact on the abundance and the type of bacteria we harbor in our gut," said Dr. Martinez-Guryn. "These microbes directly influence our metabolism and our propensity to gain weight on certain diets." Although this work is at preliminary stages, she added, "our results suggest that we can use pre- or probiotics or even develop post-biotics (bacterial-derived compounds or metabolites) to enhance nutrient uptake for people with malabsorption disorders, such as Crohn's disease, or alternatively, we could test novel ways to decrease obesity."

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