Explaining brown, white and beige fat

By Georgia Clark-Albert, Special to the BDN
Posted July 16, 2012, at 4:32 p.m.

I’m familiar with brown fat, the primary purpose of which is to regulate body temperature, and white fat cells, which are responsible for storing excess calories. Now something new has appeared in the literature. Researchers have identified that there is another energy-burning but genetically different fat cell found in adult humans that may have the potential to help in the fight against obesity and chronic diseases such as diabetes, and they have called it beige fat.

It was previously thought that only babies had brown fat to keep them warm. More recent research has found that adults also have some brown fat, but the brown fat in adults is different than the brown fat in babies. Brown fat in babies comes from muscle, but the brown fat in adults is actually what is being called the new “beige” fat and occurs from the “browning” of white fat. Beige fat cells are pea-size deposits found just beneath the skin. They are located near the collarbone and along the spine in human adults.

During exercise our muscles release the hormone irisin. Scientists at Dana Farber Cancer Institute isolated the muscle hormone and named it irisin, after the Greek messenger goddess, Iris. This hormone is believed to be responsible for the many of the health benefits of exercise.

Irisin levels rise when we exercise. Irisin converts ordinary white fat cells into beige fat cells and these cells burn up extra calories. Researchers have long known that the calories burned during exercise exceeded the number used during the actual physical activity. It is believed that beige fat could be responsible for burning these extra calories.

What is interesting is that the muscles also release irisin when the body is cold. This could mean that the beige fat mechanism might have developed as a response to shivering, which, like exercise, is classified as a neuromuscular activity. The conversion of cells to beige is not necessarily permanent. Senior author Bruce Spiegelman believes that the increase or decrease depends on physiological conditions such as age, sex and obesity level.

This might explain why more brown fat and perhaps more beige fat is present in people who are physically fit and active versus those much less fit. Both brown and beige fat contain a plethora of mitochondria, the power plants of cells that convert food into energy and generate heat. Both types contain iron as well, which gives them their distinct brown and beige tones.

The hope is that one day beige fat cells will lead to new treatments for obesity and diabetes. Further research will be crucial to determine whether anything useful can come from this discovery. Some of the questions researchers would like to know more about include:

• How much beige fat is there?

• Why do some people have a greater or lesser proportion of it than others?

• How can it be used to help people lose weight?

• Is there a way that the production of beige or brown fat can be stimulated over white fat to increase fat breakdown?

• Is there a place in all of this for drug therapy?

Always looking for a new twist, the diet gurus already have started recommending cold and shivering as an alternative to exercise. Spiegelman says forget about it. It would be a pretty uncomfortable therapy.

Georgia Clark-Albert is a registered dietitian and adjunct nutrition instructor at Eastern Maine Community College who lives in Athens. Read more of her columns and post questions at bangordailynews.com or email her at GeorgiaMaineMSRDCDE@gmail.com.

http://bangordailynews.com/2012/07/16/health/explaining-brown-white-and-beige-fat/ printed on July 31, 2014