Study: Brown Fat Burns More Calories – Who Knew?

In the seemingly endless obsession with the study of weight control — a fixation exclusive to developed countries where there’s a prevalence of obesity — two new studies suggest brown fat burns extra calories “like a furnace”.

Dr. André Carpentier, an endocrinologist at the University of Sherbrooke in Quebec and lead author of a new paper in The Journal of Clinical Investigation reports that brown fat can burn ordinary fat and that glucose is not a major source of fuel for these cells.

When the cells run out of their own small repositories of fat, they suck fat out of the rest of the body. “We have proof that this tissue burns calories,” Dr. Carpentier said. “But what happens over the long term is unknown.”

In the male oriented study, the subjects were kept chilled, “but not to the point of shivering, which itself burns calories. Their metabolic rates increased by 80 percent, all from the actions of a few ounces of cells. The brown fat also kept its subjects warm. The more brown fat a man had, the colder he could get before he started to shiver.”

Brown fat, Dr. Carpentier wrote in an accompanying editorial, “is on fire.” On average, Dr. Carpentier said, the brown fat burned about 250 calories over three hours.

New York Times writer Gina Kolata notes there is also another type of brown fat that investigators discovered it in mice years ago.

Bruce Spiegelman, professor of cell biology and medicine at the Dana-Farber Cancer Institute, and his colleagues report that in mice exercise can make it appear, by turning ordinary white fat brown.

Kolata explains that when mice exercise, “their muscle cells release a newly discovered hormone that the researchers named irisin. Irisin, in turn, converts white fat cells into brown ones. Those brown fat cells burn extra calories.”

From Professor Spiegelman’s study:

“Irisin acts on white adipose cells in culture and in vivo to stimulate UCP1 expression and a broad program of brown-fat-like development. Irisin is induced with exercise in mice and humans, and mildly increased irisin levels in the blood cause an increase in energy expenditure in mice with no changes in movement or food intake.

“This results in improvements in obesity and glucose homeostasis. Irisin could be therapeutic for human metabolic disease and other disorders that are improved with exercise.”

Spiegelman suspects humans, like mice, make brown fat from white fat when they exercise, because humans also have irisin in their blood. And human irisin is identical to mouse irisin.

“What I would guess is that this is likely to be the explanation for some of the effects of exercise,” Dr. Spiegelman says. The calories burned during exercise exceed the number actually used to do the work of exercising. That may be an effect of some white fat cells turning brown.

What can we conclude from these two studies? Well, if you swim, jog, or lift weights and reside on the North Pole, you’re in luck when it comes to keeping your weight down.