Chill Against Overweight, or What We Owe to Mice mojzagrebinfo/

Chill Against Overweight, or What We Owe to Mice


New evidence has been found that reducing ambient temperature may contribute to body weight reduction. Staying in chilly environment alters intestinal bacterial flora in a way which might help fighting overweight. This is the conclusion of experiments on mice carried out by PAS Institute of Animal Reproduction and Food Research together with a Swedish research partner. 


Apart from proper diet and exercise, anyone interested in regulating their body weight should also consider lowering temperature of their daily environment. It is recommended by scientists from PAS Institute of Animal Reproduction and Food Research, who revealed an earlier unknown correlation between ambient temperature and body weight stabilization. The results of Polish-Swedish research supervised by Prof. Leslie Kozak and Prof. Fredrik Baeckhed have recently been published in a high-impact journal, Cell Metabolism ( 

It has been known for years that low temperatures aid body weight loss and fat reduction by activating brown adipose tissue and increasing energy expenditure. Thanks to the newest discovery, another factor was revealed to support weight loss in lower temperature – changing gut microflora composition. 

Mice were chosen for tests because their intestinal bacterial flora resembles human microflora to a great extent. It turned out that if a mouse stays in cool conditions for some time, significant changes occur in its intestinal microflora. The new set of bacteria would then prevent its organism from gaining weight easily even if its diet is far from perfect. 

Doing research on gastrointestinal bacterial flora (also called gut microbiota) is very challenging. Dr. Marika Ziętak (PAS Institute of Animal Reproduction and Food Research) co-authored the research paper. In an interview for the Polish Press Agency, she said that intestinal microbiota is a very complex system, and the microbiome – the set of bacterial genes – is composed of a number of genes over 100 times higher than the number of genes found in its host. No wonder gut microbiota is responsible for some crucial processes in mammals’ organisms, such as securing the energetic balance, preventing colonization of the digestive tract by pathogenic bacteria, and breaking down undigested polysaccharides and fiber. 

Human digestive tract is inhabited by an inconceivable number of microorganisms. Dr. Ziętak  says that every person carries approximately between 100 billion and a trillion of such inhabitants. This means gut microbes contribute 1–1,5 kg to a person’s mass. It had been discovered before that intestinal bacteria may contribute to developing obesity since they help the organism to utilize carbohydrates which are difficult to digest (e.g., fiber) and thus provide additional 50–200 kcal every day. However, until recently little was known about the impact of temperature changes on gut microbiota. 

At 29° C – the ideal ambient temperature for mice – the activity of brown adipose tissue in a mouse’s organism remains very low. For man corresponding conditions exist at room temperature. During the experiment, mice were kept in ambient temperature of 29° C, but also lower temperatures activating brown adipose tissue: 17° C and 12° C. Importantly, it was noted that after 24 hours in lower temperature, a mouse’s gut microbiota composition changes. What remained unclear was how this change affects the mouse. 

In order to investigate the impact of lowered temperature, further tests were conducted on mice with sterile digestive tracts, that is, animals whose bacterial microbiota has not developed. Sterile mice were implanted gut bacteria from mice kept in lower temperatures for 4 weeks. Some sterile mice were also implanted bacteria from animals kept in ideal ambient temperature for comparison. After introducing gut microbiota, all mice were fed according to a high-fat diet. In normal conditions, this would result a rapid gain of weight in all mice. 

However, it turned out that animals with gut microbiota from mice kept in low temperatures remained slim for a long period of time (they were observed during six weeks). They also proved to have better glucose tolerance and insulin resistance, as well as lower body fat percentage despite the diet applied. At the same time, the control group of mice gained weight as it would be expected. 

The researchers investigated the origin of differences between those groups of mice. “We have proved that lowering ambient temperature and increased activity of brown adipose tissue triggered by chill provoked changes in the microbiome, which in turn led to increased production of certain bile acids conjugated with taurine. Those acids activate specific signal tracks and enhance burning fat. All that contributed to the protection of mice kept in cold against diet-related obesity” – comments Dr. Marika Ziętak. 

Dr. Ziętak thinks that those conclusions could be extended onto people. “We would like to encourage people struggling with overweight to reduce ambient temperature in their surroundings”, says the scientist. She also emphasizes that chill should be accompanied by proper diet and exercise. 

The researcher indicates that optimal ambient temperature for man is 23° C. Research carried out in 2009 ( revealed that lowering ambient temperature to 17° C for only two hours a day activates brown adipose tissue and increases energy expenditure. The recent results of Polish-Swedish research show that there is more than one way low temperature may help reduce overweight.



© PAP – Nauka w Polsce, Ludwika Tomala/ mrt/




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