Scientists from City of Hope, Broad Institute, and Keio University have discovered how specific gut bacteria interact with diet to trigger a metabolic switch that converts energy-storing white fat into calorie-burning beige fat in mice.
The study, published in Nature, reveals that a low-protein diet activates a distinct group of gut microbes. These microbes then send chemical signals throughout the body, prompting fat tissue to burn energy instead of storing it. As a result, the research uncovers a previously unknown biological pathway linking diet, the gut microbiome, and metabolic health. The findings could eventually guide the development of new therapies for obesity, diabetes, and other metabolic disorders.
Fat Tissue Is More Adaptable Than Previously Thought
Researchers have long considered fat tissue relatively stable. However, this study highlights its remarkable adaptability.
“Fat tissue is not fixed—it’s surprisingly adaptable,” said Kenya Honda, co-senior author of the study and adjunct professor at City of Hope. “We found that certain gut bacteria can sense what the host is eating and translate that information into signals that tell fat cells to burn energy.”
Most adult body fat consists of white fat, which primarily stores excess calories. In contrast, beige and brown fat burn energy to produce heat and regulate metabolism. Although babies are born with significant amounts of brown fat, these stores decline as they age. Consequently, scientists have long sought safe ways to convert white fat into beige fat—a process known as “beiging”—to improve metabolic health.
Low-Protein Diet Reveals Key Role of Gut Microbes
To explore this process, researchers fed mice a low-protein diet. Interestingly, the animals developed large amounts of beige fat only when the right gut bacteria were present.
However, when scientists fed the same diet to germ-free mice that lacked a microbiome, the fat-burning effect disappeared. This observation clearly demonstrated that diet alone was not sufficient.
“This told us the diet alone wasn’t enough,” Honda explained. “The gut microbiome was essential.”
Further analysis revealed four specific bacterial strains responsible for triggering fat browning. When researchers introduced these microbes into mice alongside the low-protein diet, the animals converted white fat into beige fat. In addition, the mice gained less weight, showed improved glucose control, and had lower cholesterol levels.
Two Microbial Signals Drive the Fat-Burning Process
As reported by medicalxpress, the scientists also discovered that gut microbes initiate fat burning through a two-step signaling process rather than a single trigger.
First, the microbes alter bile acids in the body, pushing fat cells toward a calorie-burning state. Next, they stimulate the liver to release a hormone called FGF21, which boosts metabolism.
Importantly, both signals must work together. When researchers interrupted either pathway, the fat-burning effect disappeared.
“This work underscores how the gut microbiome actively interprets what we eat and translates that information into signals the body responds to,” said Ramnik Xavier of the Broad Institute and Harvard Medical School.
According to Xavier, these insights create opportunities to study interactions between microbes, metabolites, and metabolic disease more closely, which may ultimately lead to new therapeutic strategies.
Potential Implications for Future Treatments
Although the findings are promising, researchers caution against applying them directly to humans. The low-protein diet used in the experiment is far lower than recommended for people. Moreover, earlier attempts to improve metabolism through probiotics alone have produced limited success.
Instead, the researchers believe the most promising approach lies in targeting the biological pathways activated by gut microbes rather than relying on extreme diets or bacterial supplements.
“Our goal is not to tell people to eat extreme diets,” said study’s first author Takeshi Tanoue of City of Hope and Keio University. “The real opportunity is to understand these pathways well enough to design therapies that safely mimic their benefits.”
Expanding Understanding of Metabolism and Disease
Obesity and metabolic disorders significantly increase the risk of conditions such as cancer, diabetes, and cardiovascular disease. By demonstrating how gut microbes and diet reshape fat tissue, this study adds an important piece to the puzzle of how metabolism, inflammation, and disease risk are interconnected.
Ultimately, the research highlights the gut microbiome as an active regulator of metabolic health.
“It doesn’t just respond to diet,” Honda said. “It interprets it.”
