Steven R. Smith, MD


June 23, 2014

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What Color Is Your Fat?

My name is Steven Smith, from Winter Park, Florida, where I serve as the Scientific Director at the Translational Research Institute for Metabolism and Diabetes, and Professor at the Sanford-Burnham Medical Research Institute.

I am at the American Diabetes Association (ADA) Scientific Sessions today, and I want to tell you about some of the emerging science around the idea of brown fat.[1,2,3] What is brown fat, and why should we be interested or concerned about it?

We all know about white fat. That's the fat that nobody wants. Let's get rid of it. White fat stores fat and is an important way, after we eat a meal, of storing our food for the long term.

On the other hand, the emerging science is telling us that there are other types of fat. One that is a hot topic here at the ADA is brown fat. Brown fat is found in a couple of areas of the body. Children have it when they are born; neonates have a lot of brown fat. It is thought to generate heat to keep a newborn warm. We used to think that brown fat involuted through life and that we didn't have brown fat later on.

Some very interesting and important clinical studies[4,5] several years ago showed that brown fat is actually present in some adults. What does brown fat do? Brown fat is brown because it contains mitochondria; those are the energy-producing organelles in each and every cell of our body. But, brown fat has a lot of mitochondria that can generate heat. Uncoupled, the mitochondria burn fat and glucose, and that generates heat to keep us warm in the cold. Until just a few years ago, the only reason we thought we had brown fat was to keep warm.

It turns out that brown fat is a lot more interesting. It can consume a lot of glucose when it's stimulated, either by cold or by hormones. We will talk about those hormones in a few minutes. But brown fat also takes up fat and burns it in a way that allows us to blow off the extra calories if we eat too much. This is important for patients with diabetes, because it is a real "glucose sink." It can suck up a lot of glucose from the blood. Several scientists, some of whose data[1] have been presented here at the ADA, have found that glucose uptake may actually help regulate the blood sugar level.

A Fat-Burning Powerhouse

Brown fat is found between the scapulae in the back as well as in the supraclavicular area, around the heart, and around the kidneys. Those fat deposits are very important for metabolism. As a person develops obesity or diabetes, these brown fat depositions seem to shrink in size and reduce their activity. A lot of basic science interest has arisen about how we might be able to flip the switch and turn these brown fat cells on to burn more brown fat and help them develop more normally.

Without going into too much detail, hormones that are secreted from the heart and other hormones appear to be able to activate brown fat to make it grow and become activated and produce more heat, and to take up that glucose and fat as well. Although hormones are important, the primary stimulus for the activation of brown fat is the sympathetic nerve terminals.

There is also some thought that the beta-blockers used to treat hypertension might actually be turning brown fat off. That may be one of the reasons that beta-blockers increase body weight. That is the story about brown fat.

Even more interesting is the idea that there might be beige or bright fat. What is that? It turns out that there is an intermediate cell type in white fat that doesn't just store fat, but also has the capacity to burn it. That is another hot topic here at that ADA meeting. This concept is newer in terms of the science that goes along with it, but it is still very intriguing. Drugs, hormones, or other environmental activation (such as a little bit of cold every day) might be able to turn on the fat-burning, so that we can take something that nobody likes (being fat) and manipulate those fat cells to burn fat and sugar.

That is some of the emerging science here at the ADA meeting. I hope you have enjoyed this discussion about brown fat -- the good fat, the new kind of fat that we are trying to turn on. Thank you for your time and attention.


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