Obesity and the Microbiome: Narrowing in on the Culprits

An interesting study just came out of the University of Chicago, looking at how specific bacteria in the small intestine affect the absorption of fat from the diet.[i]  The work should, in the long term, have huge implications for the treatment of obesity and also, illnesses where malabsorption (like Crohn’s) is problematic.

We know that the bacteria in the small intestine (where nutrient absorption takes place) changes within a day or two of eating a high-fat meal.  The microbes help facilitate the production and secretion of the enzymes necessary to rapidly break down the fat and  to digest the fatty food.  Says the study’s senior author, “”These bacteria are part of an orchestrated series of events that make lipid absorption more efficient…Few people have focused on the microbiome of the small intestine, but this is where most vitamins and other micronutrients are digested and absorbed.”[ii]

It was believed that specific microbes of the small intestine regulate the breakdown and absorption of fats.  The researchers, therefore, set out to learn which bacteria in particular are responsible.  They started with germ-free mice and found that even when fed high fat foods, they did not gain weight as the fats were excreted with their stool.  However, mice who have a very high level of non-pathogenic gut bacteria, did gain weight.  Very rapidly, the microbes in their small intestines changed, with increasing amounts of Clostridiaceae and Peptostreptococcaceae, the former of which in particular appears to be  responsible for fat absorption.  Levels of Bifidobacteriacaea and Bacteriodacaea, microbial families associated with leanness, rapidly decreased.

Another of the scientists involved in the work sums it up:  “”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…These microbes directly influence our metabolism and our propensity to gain weight on certain diets.”

It’s not just that a high-fat Western diet leads to obesity (and all the ills associated with excess weight) simply because we eat way too many calories.  The food we eat also directly impacts the bacteria in our biomes and how that food is digested and absorbed – and the health implications of that are vast.  Of course though, diet is not the only factor involved – read my post from a few weeks ago on how helminths protect against this very same obesity-from-a-high-fat-diet. With that in mind, you do have to wonder if the depletion of both our macro and microbiomes make us more prone to adverse microbial alterations from diet.

_________________________________________

[i] Kristina Martinez-Guryn, Nathaniel Hubert, Katya Frazier, Saskia Urlass, Mark W. Musch, Patricia Ojeda, Joseph F. Pierre, Jun Miyoshi, Timothy J. Sontag, Candace M. Cham, Catherine A. Reardon, Vanessa Leone, Eugene B. Chang. Small Intestine Microbiota Regulate Host Digestive and Absorptive Adaptive Responses to Dietary Lipids. Cell Host & Microbe, 2018; 23 (4): 458 DOI: 10.1016/j.chom.2018.03.011

[ii] https://www.sciencedaily.com/releases/2018/04/180411131639.htm