Brown fat, also known as brown adipose tissue, is a special kind of fat that burns energy to generate heat. It keeps small animals and babies warm, and animals with abundant brown fat are protected from diabetes and obesity. How brown fat is regulated in people, and how it relates to metabolism, have been unclear.
Endocrinologist Dr Paul Lee from Sydney’s Garvan Institute of Medical Research, recently undertook The Impact of Chronic Cold Exposure in Humans (ICEMAN) study at the National Institutes of Health (NIH) in Washington, funded as an NHMRC Early Career Research Fellow.
For the ICEMAN study, 5 healthy men were recruited and exposed to four month-long periods of defined temperature — well within the range found in climate-controlled buildings — at the NIH Clinical Centre. They lived their normal lives during the day, and returned each night to the centre, staying for at least 10 hours in a temperature-regulated room.
For the first month, the NIH rooms were maintained at 24º C, a ‘thermo-neutral’ temperature at which the body does not have to work to produce or lose heat. The temperature was then moved down to 19º C for the second month, back to 24º for the third month, and up to 27º for the fourth month.
Independent of the season during which the study was carried out, brown fat increased during the cool month and fell during the warm month.
Among the metabolic benefits of increased brown fat was heightened insulin sensitivity. This suggests that people with more brown fat require less insulin after a meal to bring their blood sugar levels down.
“The big unknown until this study was whether or not we could actually manipulate brown fat to grow and shrink in a human being,” said Dr Lee. “What we found was that the cold month increased brown fat by around 30-40%.”
“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.”
Source: Garvan Institute of Medical Research. “The ICEMAN study: How keeping cool could spur metabolic benefits.” ScienceDaily. ScienceDaily, 22 June 2014.
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