Brown fat may clear obesity-linked amino acids from blood

Scientists consider brown fat a heat organ. The person in this scan was cold. (Credit: Hg6996 via Wikimedia Commons)

New research clarifies how brown fat, also known as brown adipose tissue, may help protect against obesity and diabetes.

The study in the journal Nature adds to our knowledge about brown fat’s role in human health and could lead to new medications for treating obesity and type 2 diabetes.

Scientists consider brown fat a heat organ. People have a few grams of it in areas including the neck, collarbone, kidneys, and spinal cord. When cool temperatures activate it, the fat uses sugar and fat from the blood to generate heat in the body.

Two heat-map style images of bodies with color indicating activity in brown fat
Left: Brown fat is not activated. Right: The orange color on both shoulders and the neck show cold conditions activating brown fat. (Credit: Labros Sidossis/Rutgers)

The study shows that brown fat could also help the body filter and remove branched-chain amino acids (BCAAs) from the blood. BCAAs (leucine, isoleucine, and valine) are in foods like eggs, meat, fish, chicken, and milk, but also in supplements used by people who want to build muscle mass.

In normal concentrations in the blood, these amino acids are essential for good health. In excessive amounts, they’re linked to diabetes and obesity. The researchers found that people with little or no brown fat have reduced ability to clear BCAAs from their blood, and that may lead to the development of obesity and diabetes.

The study also solved a 20-plus year mystery: how BCAAs enter the mitochondria that generate energy and heat in cells. The scientists discovered that a novel protein (called SLC25A44) controls the rate at which brown fat clears the amino acids from the blood and uses them to produce energy and heat.

“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,” says coauthor Labros S. Sidossis, a professor who chairs the kinesiology and health department at Rutgers University-New Brunswick and a professor in the medicine department at the Robert Wood Johnson Medical School.

Next, researchers need to determine whether brown fat’s uptake of BCAAs can be controlled by things like exposure to mildly cold temperatures (65 degrees Fahrenheit) or consumption of spicy foods—or by drugs. This could improve blood sugar levels that are linked to diabetes and obesity, Sidossis says.

Source: Rutgers University