Imagine you could lose weight simply by ‘being cold’ for a couple of weeks, as a quick attack plan. Doesn’t it sound like the perfect solution?

This is what a team of scientists from the University of Geneva in Switzerland have just shown, at least in mice. According to the conclusions of a new study, recently published in Cell, being exposed to low temperatures could contribute to a subject getting leaner, partly due to gut microbes. The Swiss researchers found that exposure to low temperatures alters the make-up of intestinal microbes in rodents, causing the mice to burn fat, improve blood sugar levels and reduce body weight.

Scientists have long known exposure to cold mimics the effects of exercise. To get a better understanding of the mechanisms behind this, physiologist Mirko Trajkovski, leader of the research, designed an experiment with lab animals. First, he surveyed which microbes that live in relative comfort at a temperature of 21ºC were harboured in lab mice’s guts.

Then, from days 11 to 30, they progressively lowered the temperature to 6ºC to see whether it affected their gut microbiota. During the time the experiment lasted, scientists measured the rodents’ temperature, took samples of their stools and monitored parameters such as insulin uptake and fat type.

At the end of this period, they found that mice exposed to cold experienced a sharp shift in their microbiota composition with a key bacterium, Akkermansia muciniphila, associated with obesity and diabetes, virtually disappearing. And when that happened, both the animals and their microbes seemed less adept at wringing energy from the food they digested. Moreover, when the bacterium was artificially administered to the mice, weight loss resumed.

“We provide compelling evidence that gut microbes play a key role in our ability to adapt to the environment by directly regulating our energy balance,” said senior study author Trajkovski in a statement. In order to understand more of the impact of that bacteria shift, the researchers performed a second experiment with another group of mice, which were germ-free. They transplanted the cold-induced gut bacteria into them and consequently observed how these microbes improved glucose metabolism, increased tolerance to cold temperatures and caused weight loss in the mice.

“These findings demonstrate that gut microbes directly regulate the energy balance in response to changes in the environment,” said Trajkovski.

However, this loss of weight does not last forever. After three weeks of being exposed to the cold, the mice’s bodies started to stabilise. The study’s authors believe this may be because the intestine starts absorbing more nutrients from food in order to counteract additional weight loss.

Now, the researchers plan to study the molecular mechanisms by which gut microbes sense the changes in the environment that affect the host’s energy balance. They will also carry out further studies to see whether the results are also applicable to humans, although for the moment, Trajkovski cautiously highlights, this remains a big ‘if’.





Claire Chevalier, Ozren Stojanović, Didier J. Colin, Nicolas Suarez-Zamorano, Valentina Tarallo, Christelle Veyrat-Durebex, Dorothée Rigo, Salvatore Fabbiano, Ana Stevanović, Stefanie Hagemann, Xavier Montet, Yann Seimbille, Nicola Zamboni, Siegfried Hapfelmeier, Mirko Trajkovski. Gut Microbiota Orchestrates Energy Homeostasis during ColdCell, 2015; 163 (6): 1360 DOI: 10.1016/j.cell.2015.11.004