Mild psychological stress activates brown fat, study finds

Kurt Wood
Wed, 10 Feb 2016
Mild psychological stress activates brown fat, study finds
Mild psychological stress could activate brown fat, according to new research.

The study, conducted at The School of Medicine, University of Nottingham, could lead to new and effective treatments for type 2 diabetes.

Brown fat is one of two types of fat found in humans. The other, more common form is white fat, which is the kind of fat used to store excess calories. High levels of white fat are considered a health risk. The opposite is true of brown fat, high levels of which are considered healthier.

The purpose of brown fat is to burn calories in order to generate heat. Previously, it was thought that brown fat was only found in babies and hibernating mammals, but it was recently discovered that brown fat can also be found in adults. People with higher levels of brown fat tend to have less white fat and lower body mass index (BMI) than people with low levels of brown fat.

To do its calorie-burning job, brown fat first has to be activated. Previous studies have suggested that colder temperatures activate brown fat. It is thought that, if researchers find a way to activate and increase levels of it, brown fat could be an effective treatment for obesity. Reducing levels of obesity could, in turn, prevent many cases of type 2 diabetes.

This study found that mild psychological stress led to increased brown fat activity in five female subjects. Each participant had to do two things: first, they had to take a short maths test; then they watched a relaxation video. Using infrared thermography to measure skin temperature in the neck (the main area of brown fat), the researchers found that levels of brown fat activity were considerably higher when cortisol levels were raised - in other words, when the participants were stressed in the lead-up to the maths test.

"Our research indicates that the variation in brown fat activity between individuals may be explained by differences in their response to psychological stress," said Professor Michael E Symonds, of the School of Medicine, University of Nottingham, and co-author of the study. "This is important as brown fat has a unique capacity to rapidly generate heat and metabolise glucose."

"Most adults only have between 50-100g of brown fat but because its capacity to generate heat is 300 times greater (per unit mass) than any other tissue, brown fat has the potential to rapidly metabolise glucose and lipids. There is an inverse relationship between the amount of brown fat and BMI, and whether this is a direct consequence of having more active fat remains to be fully established.

"A better understanding of the main factors controlling brown fat activity, which include diet and activity, therefore has the potential to introduce sustainable interventions designed to prevent obesity and diabetes. In future, new techniques to induce mild stress to promote brown fat activity could be incorporated alongside dietary and/or environmental interventions. This is likely to contrast with the negative effects of chronic and more severe stress that can contribute to poor metabolic health."

The study is interesting, but it is also very small, involving as it did only five participants. Further, larger studies will be needed to validate the study's conclusions. Nevertheless, the research adds an intriguing dimension to the promising subject of brown fat.

The findings are published in Experimental Physiology.
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