A transplant of the body's "brown fat" can help to burn more calories, lower blood sugar and control weight -- at least in mice. That's the conclusion of a new study. Most people have a lot more white fat, which is often unhealthy. Brown fat is found in small amounts around the neck, collarbone, shoulders, spine and heart. Its purpose seems to be to burn calories to keep the body warm. Researchers wanted to know if a transplant elsewhere in the body would help with weight control. They took tiny amounts of brown fat from between the shoulders of mice and injected it near the white fat of the belly. They tried this first with mice of normal weight and then with overweight mice. After 8 weeks, mice that got the injections were better at converting glucose (sugar) into energy. As a result, they had lower blood sugar than mice that got a sham treatment. After 12 weeks, they weighed less than the group that got the sham treatment. Their bodies also burned more calories. The Journal of Clinical Investigation published the study. The Los Angeles Times wrote about it December 11.

By Reena L. Pande, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

All fat is not created equal. It turns out there is good fat and bad fat. The typical fat we think about is called white fat. It's the kind that isn't good for you and stores calories in the body. In recent years, though, we have begun to understand that there is another kind of fat, called brown fat, and it turns out to be good for you.

Brown fat has several important functions and may have many more effects that we do not yet understand. Brown fat:

• Generates body heat
• Burns calories
• Helps control body weight
• Improves metabolism
• Improves the body's response to insulin (a hormone that controls sugar levels)

Brown fat was first found in hibernating animals and in infants, but now we know that even adults have brown fat. Adults have tiny amounts of it hiding between the shoulder blades in the upper back, near the collarbones, on the sides of the neck, and around the heart. There may be some brown fat between muscles as well.

Brown fat also helps control body weight and metabolism. People with lower body weight tend to have more brown fat. So scientists have wondered if increasing brown fat might be one way to help people lose weight, improve blood sugar and lower the risk of obesity and diabetes.

In a new study, researchers tried to do just that. They took a small piece of brown fat from one mouse and transplanted it into another mouse. They found that this "brown fat transplant" had very positive effects. The mice that got the transplants had improved blood sugar levels and better response to insulin. These mice also had lower body weight and less overall fat. These improvements were seen even in mice that were fed a high-fat diet.

What Changes Can I Make Now?

The first question you might ask is how you can increase your own brown fat stores. Don't expect to get a human "brown fat transplant" any time soon. Even if that were to become a reality one day, experts say that the effects may be modest.

We still know that the best route to weight loss is through diet and exercise. Here's what I recommend to my patients:

• Pay attention to what you eat. Too often we lose track of the calories going in our mouths. The leftover chicken nuggets from your kids' plates, the extra handful of chips or even the large drink you get instead of a small one -- all of these can add up to extra weight. By paying closer attention, you might just find there are places you can improve and drop a few calories from your diet.
• Personalize it. What works for one person may not work for another. We are understanding more and more that there's no one right diet. Figure out what works best for you and your lifestyle. And be flexible. If one nutrition strategy doesn't work for you, try another one.
• Get moving. Starting an exercise regimen is hard, but also so good for you. In fact, exercise may be one possible way to increase brown fat. Research in mice suggests that exercise may increase brown fat stores.
• Sustain and maintain. Make sure to look for diet and exercise strategies that you can stick with in the long term.

What Can I Expect Looking to the Future?

We are far away from doing brown fat transplants, and we have a lot more to learn about brown fat. But the data from this study are very exciting. The information researchers get from these types of studies may one day lead to new medicines to treat diabetes, prevent obesity and help with weight loss. For now, stick to those tools we know best (diet and exercise), and keep your eyes open for more studies about brown fat in the future.