Brown fat may help protect the body against obesity and diabetes, scientists have claimed.
Also known as brown adipose tissue, brown fat is considered a heat organ.
People have a few grams of it in areas including the neck, collarbone, kidneys and spinal cord.
Researchers have found that when activated by cool temperatures, brown fat uses sugar and fat from the blood to generate heat in the body.
Published in the Nature journal, the study found brown fat could also help the body filter and remove branched-chain amino acids (BCAAs) from the blood.
These amino acids – leucine, isoleucine and valine – are found in foods like eggs, meat, fish, chicken and milk.
They can also be found in supplements used by some athletes and people who want to build muscle mass.
While normal concentrations of these amino acids are essential for good health, in excessive amounts they are linked to diabetes and obesity.
Scientists found people with little or no brown fat have reduced ability to clear BCAAs from their blood, potentially leading to the development of the conditions.
Co-author Labros Sidossis, chairman of the department of kinesiology and health at Rutgers University-New Brunswick, said: “Our study explains the paradox that BCAA supplements can potentially benefit those with active brown fat, such as healthy people, but can be detrimental to others, including the elderly, obese and people with diabetes.”
The researchers say the study also solved a 20-plus year mystery about brown fat – how BCAAs enter the mitochondria that generate energy and heat in cells.
They found that a novel protein controls the rate at which brown fat clears the amino acids from blood and uses them to produce energy and heat.
Next they need to determine whether uptake of BCAAs by brown fat can be controlled by environmental factors – such as exposure to mildly cold temperatures, or consumption of spicy foods – or by drugs.
This could improve blood sugar levels that are linked to diabetes and obesity, Professor Sidossis said.