Well & Good
If you avoid cooler temperatures, you might not be doing your metabolism any favours.
We're all creatures of comfort and cranking up the heat on those winter nights is just what we do. But now we're learning cooler temperatures have an upside - on our metabolism and our weight.
A new study has found that sleeping in a cooler room can boost your metabolism. It's all because cooler temperatures can stimulate the growth of 'brown fat' - a 'good' fat that's been found to burn energy in order to generate heat.
This is big news for scientists who up until now did not know if it was possible to manipulate brown fat to grow and shrink in a human being. What they've discovered is that cool environments can stimulate growth of brown fat, while warm environments lead to its loss.
The ICEMAN study, conducted at the National Institutes of Health in Washington, placed five healthy men in temperature-controlled rooms every night for four months and then tested the impact on their brown fat tissue mass.
For the first month, rooms were maintained at 24°C, a 'thermo-neutral' temperature at which the body doesn't have to work to produce or lose heat. In the second month, the temperature was moved down to 19°C, then in the third month back to 24°C, and in the fourth month up to a toasty 27°C.
Researchers found that brown fat increased during the cool month, by around 30-40%, and fell during the warmest month.
For people with diabetes or obesity, these findings bring promise, says first author of the study, endocrinologist Dr Paul Lee from Sydney's Garvan Institute of Medical Research.
Adults don't have a lot of brown fat, but those who do could be enjoying a better metabolism, better blood sugar control and a slimmer figure.
Contemporary lifestyles and widespread central heating, however, could be impairing brown fat function instead of improving it, suggests Lee.
Studies in the UK and US in the last few decades show room temperatures in people's homes have climbed from about 19°C to 22°C.
"So in addition to unhealthy diet and physical inactivity, it is tempting to speculate that the subtle shift in temperature exposure could be a contributing factor to the rise in obesity," says Lee.
More on brown fat
This latest study follows earlier research suggesting that shivering could stimulate the conversion of energy-storing 'white fat' into energy-burning brown fat (also known as brown adipose tissue).
Brown fat has received a lot of attention since a 2009 study published in the New England Journal of Medicine found that the amount of brown fat in the body inversely correlated with body-mass index, especially in older people, suggesting a link between brown fat and adult human metabolism.
As explained by Sydney's Garvan Institute of Medical Research, we are all born with supplies of brown fat around our necks - nature's way of helping us keep warm as infants. Until only a few years ago, these stores were thought to vanish in early infancy, but we now know that brown fat is present in most, if not all, adults. Adults with more brown fat are slimmer than those without, and have lower levels of glucose.
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