An international team of microbiologists has discovered that some gut microbes increase the absorption of dietary fats, allowing the host organism to extract more calories from the same amount of food.

“This study is the first to demonstrate that microbes can promote the absorption of dietary fats in the intestine and their subsequent metabolism in the body,” said Dr John Rawls of the University of North Carolina, a senior author of the study published in the journal Cell Host & Microbe.

“The results underscore the complex relationship between microbes, diet and host physiology,” he added.

Previous studies showed gut microbes clearly impact the host’s energy balance, but their role in dietary fat metabolism was less clear, until now.

The new study was carried out in zebrafish, which are optically transparent when young. By feeding the fish fatty acids tagged with fluorescent dyes, the team was able to directly observe the absorption and transport of fats in live animals.

The scientists determined that one type of bacteria, called Firmicutes, is instrumental in increasing fat absorption. They also found that the abundance of Firmicutes in the gut was influenced by diet. Fish fed normally had more Firmicutes than fish that were denied food for several days. Other studies have linked a higher relative abundance of Firmicutes in the gut with obesity in humans.

The findings indicate that bacteria in the gut can increase the host’s ability to absorb fat and thereby harvest more calories from the diet. Another implication is that a high-fat diet promotes the growth of these fat-loving Firmicutes, resulting in more fat absorption.

“The unique properties of zebrafish larvae are helping us develop a better understanding of how the intestine functions with the goal of contributing to ongoing efforts to reduce the impact of diseases associated with altered lipid metabolism, such as diabetes, obesity, and cardiovascular disease,” said co-author Dr Steven Farber of the Carnegie Institution for Science’s Department of Embryology in Baltimore.

Although the study involved only zebrafish, not humans, it offers insights that could help inform new approaches to treating obesity and other disorders.

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Bibliographic information: Ivana Semova et al. 2012. Microbiota Regulate Intestinal Absorption and Metabolism of Fatty Acids in the Zebraﬁsh. Cell Host & Microbe, volume 12, issue 3, 277-288; doi: 10.1016/j.chom.2012.08.003