The Mycobiome, Diet and Weight

The big biome buzz over the last few days has been about research out of the University of Alabama at Birmingham which showed, in a mouse model, that the fungi of the gut – the mycobiome – plays a major role in how processed foods are digested and how body mass is distributed.[i]

To conduct this research, the scientists got genetically identical mice from 4 different labs, ensuring that their gut bacteria and yeasts were not exactly the same. Starting then with these diverse gut compositions, they measured the effects over time of dietary differences.  The mice’ diets were either standard chow or highly processed food made to resemble a typical American diet.  After 6 weeks, the researchers measured their body fat, as well as the genes and hormones involved in metabolism. They also analyzed the yeasts found in the foods themselves so they’d know what were from external sources versus what species were commensal.

What did they find?  Variations in the composition and abundance of the mycobiome determined host metabolism. Essentially “junk” food (highly processed foods) changed the composition of the fungi in the jejunum (part of the small intestine) in mice, which, in turn, led to metabolic changes: “Eating processed food made most mice fatter, but how much weight and how their metabolism changed varied between mice with different microbiomes.”[ii] Variations in the composition of the mycobiome, especially increased amounts of Termocyces and lower levels of Saccharomyces were the most strongly associated with metabolic disturbances and with weight gain (about 15% more).  Says the lead researcher, “”We showed that the gut mycobiome of healthy mice was shaped by the environment, including diet, and that it significantly correlated with metabolic outcomes…”[iii]

Next steps in this research is to look at humans and mice to learn more about how the mycobiome influences metabolism and weight gain in a high-fat diet and also, after weight loss surgery.  The scientists also hope to transplant human microbiomes into mice to see the effects.  Considering how little research has been done on the effects of the mycobiome on human health – and the effects of diet on the mycobiome – this is pretty exciting research:  “We demonstrate that exposure to processed diet leads to persistent differences in fungal communities that significantly associate with differential deposition of body mass in male mice compared to mice fed standardized diet.”

Still, yet again (for the billionth time), it struck me how insanely complex this all is.  Does diet directly dictate the composition of the mycobiome?  We know diet alters the bacterial microbiome – so does this, in turn, affect the mycobiome?  Or are both true? Time will tell.  I’ll be following these developments closely.

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[i] Tahliyah S. Mims, Qusai Al Abdallah, Justin D. Stewart, Sydney P. Watts, Catrina T. White, Thomas V. Rousselle, Ankush Gosain, Amandeep Bajwa, Joan C. Han, Kent A. Willis, Joseph F. Pierre. The gut mycobiome of healthy mice is shaped by the environment and correlates with metabolic outcomes in response to diet. Communications Biology, 2021; 4 (1) DOI: 10.1038/s42003-021-01820-z

[ii] https://theconversation.com/fungal-microbiome-whether-mice-get-fatter-or-thinner-depends-on-the-fungi-that-live-in-their-gut-155942

[iii] https://www.sciencedaily.com/releases/2021/03/210305123802.htm