How gut microbes make you fat

Scientists have found evidence that gut bacteria may affect circadian rhythms and metabolism leading some people to gain extra weight.

Circadian rhythms are physical, mental and behavioural changes that follow a roughly 24-hour cycle. These rhythms are communicated and carried out via signals sent from the brain and liver.

Researchers found that mice with a normal set of gut microbes showed evidence of a regular daily microbial cycle, with different species flourishing in different parts of the day and producing different compounds as a result.

These compounds appeared to act on the liver and affected how circadian clock genes were expressed in the liver.

A high-fat diet reduced the variation in the microbial cycle. The circadian clock genes were disrupted and the mice gained weight.

Meanwhile, "germ-free" mice raised without a normal gut microbiome showed evidence of a disrupted circadian clock cycle, but did not gain weight even on a high-fat diet.

The team that included researchers from University of Chicago hypothesise that high-fat diets change the compounds that microbes produce, thus disrupting the liver's circadian clock signaling.

"The earlier explanation for microbiome-related weight gain was that some bacteria make calories from food more available to your body, but this is a fundamental alternative explanation," said Jack Gilbert, microbial ecologist at the US Department of Energy's Argonne National Laboratory.

"We would like to more rigorously explore what kinds of diets trigger this response," he added.

All humans have a set of bacteria, viruses and fungi living in our guts called the gut microbiome which helps us digest food.

These also interacts with the body in a number of other ways. There is evidence that these affect allergies, mental health weight and other metabolic conditions.

The study appeared in the journal Cell Host & Microbe.