Adipose Tissue: An Endocrine Organ
Anne L. Peters, MD: Hi. I'm Dr Anne Peters, at the European Association for the Study of Diabetes (EASD) meetings in Vienna. I am here with Matthias Blüher, who is professor at the University of Leipzig in Germany and an expert in adipose tissue.
I can't think of a single patient—thin or fat—who is not interested in adipose tissue, at least their own adipose tissue. Why don't you tell me about your research and what it means?
Matthias Blüher, MD: I am happy to talk about adipose tissue. I talk to my patients all the time about adipose tissue, as you do, and I am fascinated by it. We have learned during the past 10-15 years so much about adipose tissue as an active endocrine organ. We thought adipose tissue was simply an insulator to protect us from cold and damp, and a triglyceride storage organ, but it became clear exactly 20 years ago that adipose tissue produces hormones such as leptin and signals the energy status to the brain and other organs.
How Much Brown Adipose Tissue Do We Have?
Dr Peters: What specific component of adipose tissue have you been discussing at these meetings? Is it brown adipose tissue? What is it all about?
Dr Blüher: One of the emerging research fields in understanding adipose tissue biology is to investigate brown adipose tissue. We know that brown adipose tissue may protect rodents (such as mice and rats) from the cold in winter. They have a lot of brown adipose tissue in the interscapular region—the neck region—because brown adipose tissue produces heat. It keeps the animals warm.
We thought that brown adipose tissue was something that we wouldn't find in adult humans. We know that newborns have a lot of brown adipose tissue because they cannot produce heat by muscle shivering. So newborn humans also have brown adipose tissue, but it is lost rapidly during the first 1-2 years of life. Recently, it was discovered that even adult humans may have brown adipose tissue. It is only 20-30 g of tissue weight per body, so we are not talking about a big organ here.
Dr Peters: How much other fat does the standard-size human have?
Dr Blüher: I weigh 90 kg and I have 30-35 kg of fat.
Dr Peters: So, brown fat is a tiny percentage of your total fat, if you have any.
Dr Blüher: Absolutely, and it is difficult to quantify with any of the measurement scales that we have, so we need sophisticated methods such as PET-CT to discover brown adipose tissue.
Dr Peters: In the rodents, you say that it keeps them warm, so it burns calories, correct? Are these brown fat–containing rodents lean?
Dr Blüher: This is almost exactly the content of the session that I had the pleasure to chair here at the EASD meeting. The rodents showed that the more brown fat you have, the leaner you are and the more likely that you are a healthy (nondiabetic) individual.
Dr Peters: Does brown fat improve insulin sensitivity?
Dr Blüher: It does seem to improve insulin sensitivity. That is new evidence,[1] because the individuals who have more brown fat burn more fatty acids and more glucose, and this leads to an increased resting metabolic rate, keeping them leaner.
The Seasonality of Brown Fat
Dr Peters: That is what all my patients want—an increased metabolic rate so they can burn up their calories, or at least the calories that they eat. Do you think this is going to have implications for human beings?
Dr Blüher: The entire basic research effort aims to find a clinical application, to translate what we find not only in the rodent models, but in the human models, to a clinical application. Thyroid hormones and cold stimulation increase brown fat, so there is a seasonality factor. One talk in the session was about the seasonal expression of brown adipose tissue.[2] In winter we seem to have more brown fat than in summer.
Dr Peters: Is that true in everybody or is it different in different ethnicities or populations?
Dr Blüher: There is perhaps a bias from the researchers who come from Finland, which is most likely a colder country than the places where we are living, but it is also true in The Netherlands and the United States (both north and south). It is an intrinsic rhythmicity, because we also see it in people who live in warmer areas of the world with a more stable temperature.
Dr Peters: Is it more environmental or inherited? I live in Los Angeles, and it is not particularly cold there. Would you argue that you wouldn't see much brown fat in people who live there? There are a lot of lean people in Los Angeles.
Dr Blüher: I wouldn't expect brown fat or seasonality of brown fat to necessarily only occur in very cold areas. On the other hand, the data that I have seen at the symposiums suggest that there are some intrinsic rhythms, perhaps because we are related to hibernating species, and this is something that we kept through evolution—this circannual or seasonal variation in brown fat. This may have protected us 10,000 or 20,000 years ago against our environment, but we don't need it anymore, and therefore it is lost in 80% to 90% of the patients we see.
Brown Fat: Hype or Helpful?
Dr Peters: If there was magic, would you give people more brown fat? What do you think—is it a good thing? Should I go back to Wisconsin, where I'm from? What is your sense of the role of brown fat in treating human illness or diabetes?
Dr Blüher: So far, I think it is hype. People jump on the brown adipose tissue story because there is a big hope that simply by switching on brown adipose tissue, people will be able to lose weight and improve their metabolism. At least the correlative data suggest that the more brown fat you have, the more metabolically healthy you are and the leaner you are, so there are at least suggestions that this could help.
On the other hand, we don't have a lot of intervention studies that induce brown adipose tissue. At the symposium I chaired, there were talks dealing with that.[3,4] They used cold blankets to cool patients down to 17º C—not too bad—but the temperature where we feel comfortable is most likely between 28º and 32º C, so 17º C is already cold and may induce brown fat.
Dr Peters: Did it work?
Dr Blüher: Well, we also have data demonstrating that when I put people in my research group into the cold room (4° C) for 10 minutes a day—not naked; they are well dressed—they lose weight. They lost 2-3 kg in 4 weeks with this intervention, so inducing brown fat development in adult humans might be easy to achieve through cold exposure.
Dr Peters: These people aren't shivering under those cold blankets—they are just chilling? Does it make their body temperature colder? Is that how you are inducing brown fat?
Dr Blüher: That is right. We cannot exclude the possibility that they are having some increased muscle activity, and there are big differences between the individuals. It could be that some of them have a better ability to respond with muscle shivering, but some of them at least only chill. The PET scan data suggest that you may be able to increase your brown fat mass that way.
Dr Peters: This is very good news for women of a certain age who like to cool down their rooms at night. It gives us another reason to keep ourselves cooler. It is fascinating.
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Cite this: How Promising Is Brown Fat for Weight Loss? - Medscape - Oct 02, 2014.
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