A study in the US and Japan has uncovered how certain gut bacteria can activate calorie-burning fat in mice, shedding light on obesity, diabetes and related diseases.

Most body fat in adults is white fat, which stores excess calories. In contrast, beige and brown fat burn energy to produce heat and help regulate metabolism. Scientists have long sought safe ways to convert white fat into beige fat as a potential treatment for metabolic diseases.

Researchers from City of Hope and the Broad Institute (US), and Keio University (Japan), found that mice fed a low-protein diet converted white fat into beige fat, gaining less weight and showing improved blood sugar levels and lower cholesterol levels. When the same diet was given to animals that lack gut bacteria (germ-free mice), the increase in beige fat disappeared.

The researchers isolated gut bacteria from four human volunteers with active beige fat and transplanted them into germ-free mice fed the low-protein diet. Animals receiving bacteria from two of the donors began converting white fat into beige fat. By removing one strain at a time, the team identified four bacterial strains that were essential for this process.

Moreover, researchers also found that gut bacteria responding to a low-protein diet alter bile acids, triggering the conversion of white fat into calorie-burning beige fat and stimulating the liver to release FGF21, a hormone that boosts metabolism.

Although a low-protein diet is not recommended for humans, these findings could inform therapies able to stimulate energy-burning fat without requiring major dietary changes.
“What these findings tell us is that the microbiome is incredibly important in fine-tuning things like how our body stores fat,” said Ramnik Xavier, from the Board Institute and senior co-author of the study published in Nature.