Well, one type of fat. Research shows adults have large, active deposits of "brown fat," a type of energy-burner once thought to disappear after infancy. Scientists hope it may lead to ways to fight obesity.
Three new studies published this week in The New England Journal of Medicine confirm that adults have stores of adipose tissue that burns energy, rather than storing it like better-known "white" fat, reports Time. Scientists have known for years that rodents and newborns have large deposits of the fat, which contains a high concentration of dark-colored mitochondria. The tissue burns sugar and releases the energy as heat, which allows mice and babies to shiver to keep warm in cold temperatures.
As humans develop the ability to regulate their body temperature, they lose the brown fat cells, which are mostly present in a sheet on a baby's back. Now scientists have found that adults actually retain large stores of brown fat in deposits around the neck. Scientists studying cancer patients have known for years that there are spots on the neck that burn a large amount of glucose, but they didn't know what they were looking at. Usually, that indicates a growing tumor, but biopsies would show the spots were not cancerous.
"It is, in a sense, the discovery of a new organ," said Sven Enerback, lead author of one of studies, reports The Washington Post. People with the most active brown fat are cancer patients and people with hyperthyroidism. Women, thinner people, and younger people, also had more brown fat than men or people who are older and fatter. The studies showed that brown fat is activated by cold. Subjects left in an ice bath or a 61 degree room for two hours showed more brown fat activity than those in warm conditions because their bodies were trying to generate heat. The New York Times reports that the fat can also be triggered by catecholamines, hormones that regulate part of the fight or flight response.
Currently the drugs that stimulate those hormones have too many side effects, but doctors hope that in the future a drug that will safely trigger brown fat will be developed. However at this point, scientists are not sure that brown fat will necessarily lead to burning white fat, since the body tries to maintain equilibrium and may alter other metabolic systems to try to make up for the loss.
[Image via Flickr.]
Study: A Fat That Helps You Lose Weight? [Time]
Studies Find A Way Adult Bodies May Fight Obesity [The Washington Post]
Brown Fat Identified As Heat-Yeilding Cells In Humans [The New York Times]