Gut Bacteria, Exercise and Insulin Resistance

I found this really interesting:  did you know that some people “…do not respond or negatively respond to exercise in terms of insulin sensitivity and blood sugar balance for reasons that remain unknown”?  I did not, although I suppose I would have guessed as much.

Researchers from the University of Hong Kong looked at the gut microbiomes of 39 prediabetic (so already showed signs of insulin resistance) overweight or obese men, half in an exercise group, half kept sedentary for the 12 week study.[i]  At the end of the study, the men were classified as either responders or non-responders depending on blood sugar levels and insulin sensitivity.  Those who responded to exercise had higher amounts of the kinds of bacteria that produce short-chain fatty acids (SCFAs), which are critically important in regulating energy and glucose levels, as well as inflammation levels: “…responders were characterized by a 3.5-fold increase of Lanchospiraceae bacterium (a butyrate-producer)…”  They also had an “…increased growth rate of several species in Bacteroides genus, most of which are propionate producers…”

The non-responders in the exercise group, on the other hand, showed “…increased production of metabolically detrimental compounds,” i.e. an increase in the production of the amino acid, glutamate, which is found to be increased in those with insulin resistance and higher levels of inflammation.  Their gut bacteria profiles similar to the sedentary group.

All the participants in the exercise group did achieve some weight loss, an improvement in lipid profiles (i.e. triglycerides and cholesterol), cardiovascular fitness and so forth.  However, the non-responders did not show response in fasting glucose and insulin levels.  The increased SCFA production seen in the responder group is really interesting, I think:  the anit-diabetic drug, Metformin, which I have written about before, is thought to work by increasing the production of SCFAs.  Remember though:  while some studies have shown that supplementing proprionate reduced fasting glucose levels, others have shown the opposite.  Remember my post from last September on that Harvard proprionate study?

That’s the thing about SCFAs:  too much is just as bad as too little.  Read this post on the subject.

It gets even more interesting.  The scientists used fecal microbiota transplant to transfer the gut bacteria from the responders and non-responders into mice.  Not surprisingly, only the microbiomes of the responders alleviated insulin resistance in obese mice.  Other studies have shown, by the way, that FMT from healthy individuals into those with metabolic syndrome has worked as well.

Why people undergo different microbial changes doing the same thing, i.e. exercising, is currently unknown.  These researchers theorize that there may be subtle differences in the gut bacteria of people that cause varying response to increased oxidative stress from exercise, for example.  Remember that people do respond differently, in terms of insulin response, to the same foods; it’s all based on individual microbiome composition.  (You can read about that here.)

The hope is, of course, that some day soon, microbiome analysis will reach the stage wherein programs to achieve and maintain health (i.e. the right diet, the right exercise, the right probiotic to tweak the biome, etc.) will be the  norm.

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[i] Liu et al., Gut Microbiome Fermentation Determines the Efficacy of Exercise for Diabetes Prevention. Cell Metabolism, 2019. doi:  10.1016/j.cmet.2019.11.001