DIETARY FATTY ACIDS SUSTAIN GROWTH OF HUMAN GUT MICROBIOTA.

While a substantial amount of dietary fats escape absorption in the human small intestine and reach the colon, the ability of resident microbiota to utilize these dietary fats for growth has not been investigated in detail. In this study we used an in vitro multi-vessel simulator system of the human colon to reveal that human gut microbiota is able to utilize typically consumed dietary fatty acids to sustain growth. Gut microbiota adapted quickly to a macronutrient switch from a balanced Western diet type medium to its variant lacking carbohydrates and proteins. We defined specific genera that increased their abundance on the fats-only medium, including Alistipes , Bilophila , and several genera of class Gammaproteobacteria. In contrast, abundances of well-known glycan and protein degraders including Bacteroides , Clostridium , and Roseburia were reduced in such conditions. Predicted prevalences of microbial genes coding for fatty acid degradation enzymes and anaerobic respiratory reductases were significantly increased in the fats-only environment, whereas the abundance of glycan degradation genes was diminished. These changes also resulted in lower microbial production of short chain fatty acids and antioxidants. Our findings provide justification for the previously observed alterations in gut microbiota observed in human and animal studies of high-fat diets. Importance Increased intake of fats in many developed countries raised awareness of potentially harmful and beneficial effects of high fat consumption on human health. Some dietary fats escape digestion in the small intestine and reach the colon where they can be metabolized by gut microbiota. We show that human gut microbes are able to maintain a complex community when supplied with dietary fatty acids as the only nutrient and carbon sources. Such fatty acid based growth leads to lower production of short chain fatty acids and antioxidants by community members, which might potentially have negative health consequences on the host.