01.08.2016 change 01.08.2016

In a cold environment intestinal bacteria may help fight obesity

Lowering ambient temperature can help reduce body weight. Scientists have new evidence of that. When you stay in the cold, intestinal bacterial flora changes and can help in the fight against overweight - believe Polish researchers who have tested this phenomenon in mice.

Want to drop your weight? In addition to a proper diet and exercise you could also think about lowering the temperature in the rooms you stay in. This method is recommended by researchers from the Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences in Olsztyn. Their research shows a new link between ambient temperature and the body weight. The results of the Polish-Swedish study led by Prof. Leslie Kozak and Fredrik Baeckhed has been published in the prestigious journal "Cell Metabolism".

The fact that lower temperatures have a positive impact on reducing body weight and fat mass has been known for years - when it is cooler, brown adipose tissue activates in the human body and the body expends more energy. Now we know that there is one more factor that may be associated with lower temperatures and body weight decrease. It is a change in the composition of intestinal bacteria.

The tests were performed on mice, because intestinal bacteria composition in these animals is very similar to that in humans. It turned out that if a rodent remains in a cool environment for some time, substantial changes in the bacterial flora of the intestines occur. A new set of bacteria can prevent the mouse from getting fat easily - even if its diet is not perfect.

LITTLE FRIENDS

The study of bacterial flora of the gastrointestinal tract (the intestinal microbiota) is a big challenge. Co-author of the publication Dr. Marika Ziętak from the Institute of Animal Reproduction and Food Research PAS said in an interview with PAP that the intestinal microbiota is all very complex ecosystem and the set of bacterial genes is 100 times greater than the number of host\'s genes. In mammals, the intestinal microbiota has important functions, including ensuring energy balance of the body, preventing the colonization of the digestive tract by pathogenic bacteria and helping break down undigested polysaccharides and fibre.

According to the researcher, human gastrointestinal tract is inhabited by an unimaginably large number of microorganisms. It is estimated that each of us has a 100 billion or even trillion (thousand billion) of such tenants. In a single person these organisms weigh a total of 1-1.5 kg. It has already been shown that intestinal bacteria can contribute to the development of obesity - they help the body break down the compounds that are difficult to digest (dietary fibre), which provides additional 50-200 kcal per day. But it has never been shown how intestinal microbiota responds to changes in ambient temperature.

COLD RODENTS

An ideal ambient temperature for mice is 29 deg. C. At this temperature, the activity of the brown adipose tissue is very low. In humans, these conditions are met at room temperature. As an experiment, the mice were kept in 29 deg. C, and in lower temperatures, which activate brown adipose tissue: some in 17 deg. C, some in 12 deg. C. Scientists noticed that after only 24 hours in a cooler environment the composition of the intestinal microbiota in the rodent changed. They only had to see how this change affected the mouse.

For this purpose, they used mice with a sterile gastrointestinal tract. In these rodents intestinal microbiota is not developed. Such sterile mice received intestinal bacteria from "cooled" mice, held in cold conditions for four weeks. For comparison, other mice were transplanted with bacteria from the mice kept in normal temperatures, which did not have to cope with the cold. After moving to the intestinal microbiota to recipients, all mice received high-fat diet - in normal conditions animals so fed would quickly gain weight.

It turned out that mice with a set of bacteria from peers kept in the cold remained thin for a long time (they were tested for six weeks), had improved glucose tolerance, insulin sensitivity and lower percentages of fat in the body. And yet - because of the diet - the animals should not remain slim. At the same time, control mice - with bacteria from mice kept in standard, warm conditions, gained weight as expected.

The researchers examined the reasons for these differences. "We have demonstrated that lowering the temperature of the environment with increased activity of the brown adipose tissue resulted in changes in microbiome, which in turn led to increased production of certain bile acids - conjugated to taurine. They activate specific signalling pathways and enhance fat burning in the body. This resulted in the protection of against the development of diet-related obesity in mice" - said Dr. Marika Ziętak.

OF MICE AND MEN

Dr. Ziętak believes that the conclusions of the research can be translated to people. "We would encourage people struggling with overweight to reduce the temperature of their environment a little" - said the scientist. She emphasised, however, that lowering the temperature should be combined with diet and physical activity.

The researcher commented that optimum ambient temperature for humans is 23 deg. C. The study completed a few years ago showed that lowering the temperature to 17 deg. C for two hours per day leads to activation of brown adipose tissue and increased energy expenditure. Polish-Swedish research shows that this is not the only reason why low temperature may help in the fight against obesity.

PAP - Science and Scholarship in Poland, Ludwika Tomala

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