--- title: This Gut Microbe May Help Weight Loss description: A new study in mice helps explain how gut bugs, including Akkermansia, influence the development of brown fat canonical: https://time.com/4148177/microbiome-microbes-brown-fat/ author: Mandy Oaklander article:opinion: false article:content_tier: free article:published_time: 2015-12-14T22:12:27.000Z article:modified_time: 2026-02-22T13:21:33.371Z article:section: Health og:title: How Bacteria and Brown Fat Can Spur Weight Loss og:description: A new study in mice helps explain how gut bugs, including Akkermansia, influence the development of brown fat og:url: https://time.com/4148177/microbiome-microbes-brown-fat/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltc56bd09f6b6c17ad/6987788e5f570f6560b148ec/health-weight-scale-2.jpg?branch=production&width=3840&quality=75&auto=webp&crop=16:9 og:image:width: 1200 og:image:height: 675 og:image:alt: TIME.com stock photos Weight Loss Health Exercise Scale og:type: article twitter:card: summary_large_image twitter:title: How Bacteria and Brown Fat Can Spur Weight Loss twitter:description: A new study in mice helps explain how gut bugs, including Akkermansia, influence the development of brown fat twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltc56bd09f6b6c17ad/6987788e5f570f6560b148ec/health-weight-scale-2.jpg?branch=production&width=3840&quality=75&auto=webp&crop=16:9 ---  # How Bacteria and Brown Fat Can Spur Weight Loss  by [Mandy Oaklander](https://time.com/author/mandy-oaklander/)  ## Mandy Oaklander Oaklander is a senior editor at TIME. Dec 14, 2015 10:12 PM UTC  Elizabeth Renstrom for TIME  by [Mandy Oaklander](https://time.com/author/mandy-oaklander/)  ## Mandy Oaklander Oaklander is a senior editor at TIME. Dec 14, 2015 10:12 PM UTC As a human, you’re undoubtedly familiar with white fat: the pillowy kind under the skin that stores calories and excess energy. But there’s another type called brown fat, which burns extra calories, generates heat and may spur weight loss. It’s not yet clear exactly _how_ some fat browns, but finding out could prove important to weight loss interventions. Animals, including us, develop more brown fat when they’re exposed to cold, and now, a new [study](http://www.cell.com/cell/fulltext/S0092-8674%2815%2901484-1) published in the journal _Cell_ finds that gut microbes change when mice are exposed to cold, and that shift is enough to burn fat, develop brown fat and help mice lose weight. For a month, the researchers put a group of mice in a special climate chamber that gradually grew colder and colder—similar to what happens in some mice’s natural winter habitat. They kept a group of mice in room temperature to act as the control group and collected fecal samples from both throughout the month. **MORE**: [A Fat-Burning Gene May Help Weight Loss](http://time.com/4003974/gene-burns-fat/) As the mice got colder, they lost weight—but that stopped after a few days once their bodies adapted. The researchers found that the mice got better at harvesting calories from their food, because their intestines and villi that absorb nutrients in the gut became longer. The cold had created a supercharged gut, one that got more calories from the same amount of food. Even more surprisingly, their composition of gut bacteria shifted. “We found that the microbiota was dramatically changed after cold exposure,” says senior study author Mirko Trajkovski, professor in the department of cell physiology and metabolism at the University of Geneva in Switzerland. He and his team had a hunch that this bacterial shift was influencing weight loss. So they took microbes from both groups of mice and transplanted them into mice that had been bred without any bacteria at all. The mice who got the “cold” microbes started exhibiting changes like the cold mice had; they developed more brown and beige fat, lost weight and had better insulin sensitivity (which helps them adapt to the cold). They even grew longer intestines than the warm-transplanted mice, just like the cold mice had. “What was amazing is that the transplanted mice with the cold microbiota that had never been exposed to cold before were completely protected against hypothermia,” Trajkovski says. “Microbes alone were sufficient to induce this.” **MORE**: [Scientists Find A Way To Trigger Fat-Burning Brown Fat](http://content.time.com/time/health/article/0,8599,1987987,00.html) But how? The researchers wanted to see if they could pinpoint the bacterial strain associated with these benefits, and they could: a strain called _Akkermansia muciniphila_. When mice were exposed to cold, their levels of that bug disappeared. But when the scientists grew _Akkermansia_ in the lab and put it back into the mice, the mice start losing weight again. This isn’t the first time scientists have found that the _Akkermansia_ bug might play a role in weight loss. A June study of 49 overweight and obese adults found that those who had higher levels of the gut bug had [better clinical measures after going on a diet](http://time.com/3936636/diet-gut-bacteria/), including a stronger decrease in visceral fat than those with lower _Akkermansia_ levels. One guess is that lower levels of this bug may make animals absorb more calories from their food—and that this could be playing a role in human obesity. “Perhaps putting it back in in humans could be a novel way of promoting weight loss, by shrinking the gut or decreasing the absorptive surface,” Trajkovski says. “We haven’t done the studies yet.” Obviously, more research is needed before we see _Akkermansia_ weight loss shakes or brown fat in a bottle. 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