What Is Brown Fat? 8 Key Facts to Boost Your Metabolism

Updated: Jan. 28, 2021

This special type of fat—found in small amounts—can burn calories at a very high rate. Here’s how to activate your brown fat cells to help speed up weight loss.

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Brown fat burns more calories

Unlike white fat—which makes up the vast majority of the fat in our bodies and is used to store any excess calories we consume—brown fat actually burns calories to produce heat (under the right conditions). In fact, when fully activated, brown fat generates three hundred times more heat than any other tissue in the body. Just two ounces of brown fat appear capable of burning several hundred calories per day—the equivalent of a 30-minute bout of exercise. Most adults have small pockets of brown fat.

Brown fat is typically located in the sides of the neck—sometimes running down into the shoulder and upper arms—and in the region just above the collarbone. Other common locations include the upper back between the shoulder blades and along the sides of the upper spine. The amount of brown fat generally adds up to a couple of ounces at most. Because they are so small and lie deep under the skin, they don’t appear as bulges, like love handles. (Try our other proven metabolism-boosting tricks.)

Cold temperatures activate brown fat

In one study, Swedish researchers scanned five subjects after they’d spent two hours at temperatures ranging from 63°F to 66°F. During the scan itself, the subjects cooled their body temperature even further by repeatedly placing one foot in ice water for five minutes at a time, followed by five minutes out of the water. The investigators found not only that all the subjects had detectable brown fat deposits, but that the added exposure to the cold ice water boosted their brown-fat activity 15-fold. (Check out what a single workout can do for your metabolism.)

Brown fat improves your blood sugar metabolism

Brown fat may have unique diabetes-fighting properties: People with lower glucose levels tend to have more brown fat than those with higher levels, which indicates that it may play a direct role in glucose control. One group of investigators, for example, recently found that a certain protein in brown fat appears to enhance the metabolism of white fat. When they studied a strain of experimental mice who were lacking this protein, the mice expended less energy, gained weight, and developed diabetes.

In another study at Joslin Diabetes Center (where I am research director), a research team transplanted a small amount of brown fat from one group of mice into the abdomens of another group. The results were astonishing: After eight weeks, the mice given the transplants were not only leaner than a placebo group but also processed blood glucose better and had reduced insulin resistance. (Learn the 10 sneakiest foods that can wreak havoc on your blood sugar.)

Brown fat can increase your metabolic set point

This setpoint is the level of body weight at which the brain automatically begins to slow metabolic activity, making it more difficult to lose additional weight. By revving metabolic activity, brown fat could help combat the metabolic slowdown that occurs when people start dieting. If someone is able to burn an extra 200 or 300 calories a day through their brown fat, that’s enough to shed a pound of body fat in just a couple of weeks. As Americans get older, we typically add 10 pounds of weight per decade. The calorie-burning boost from brown fat could be enough to reverse this weight gain and help older individuals maintain the body fat they had as young adults.

To activate brown fat, expose your skin to cool temperatures

Cold temperatures send a signal to your brain, which then acts to stimulate brown fat activity in two ways: by acting on your vascular system directly to increase blood flow to your brown fat stores and by sending nerve impulses to brown fat cells that stimulate an additional boost in cellular activity. How cold do you have to be? Researchers have found that sitting in a 59°F room for two hours wearing summer clothing will stimulate brown fat to burn an extra 100 to 250 calories, depending on the individual. A Japanese research team found that half of the subjects under age 38 showed signs of brown fat activation in a 66°F setting. (Results were less impressive for people older than 38.) Lowering your home’s thermostat to the mid-60s or below may be enough to stimulate at least some brown fat activity.

Exercise in cool temps

Boost the number of calories you burn during exercise by stimulating your brown fat stores during your workout. Exercise in temperatures that are 62°F to 64°F or lower. Even better: Make sure your skin is exposed, because the evaporation of sweat as you exercise adds to the cooling effect. What you don’t want to do: Increase how much you perspire by turning up the heat when you exercise. This hotter environment will actually shut down brown fat activity.

Consider a low-fat, high-carb diet

Although there’s no firm evidence that any specific foods or nutrients can activate brown fat, it’s interesting to note that radiologists—who want to decrease brown fat activity when doing scans of cancer patients, because the heat generated by activated brown fat makes it harder to see tumor-related activity—routinely recommend that patients eat a high-fat, low-carb diet before scans, on the grounds that this reduces brown fat activation. This suggests that a low-fat, high-carb diet will boost brown fat activity. (Try these other diet tweaks to help you lose weight.)

Eat more apples—with the peel on

Ursolic acid—a substance that occurs in high concentrations in apple peels—increases brown fat and muscle mass, while at the same time reducing obesity and improving glucose tolerance. Other foods that contain ursolic acid include cranberries, blueberries, plums, and prunes, as well as the herbs oregano, thyme, lavender, holy basil, bilberry, devil’s claw, peppermint leaves, periwinkle, and hawthorn. Animal studies have also found that the herb bitter melon appears to increase brown fact activity.

Avoid, reverse, and control diabetes

In his book The Diabetes Reset (Workman Publishing, 2015), George King, MD, research director and chief science officer at Harvard’s Joslin Diabetes Center, translates the latest cutting-edge research about nutrition, metabolism, and more into a diet and lifestyle plan to prevent and treat diabetes.

Reader's Digest
Originally Published in Reader's Digest