Wednesday Bubble: not for naught, brown fat

Posted by Liz on Jan 25, 2012 in exercise, weight | 10 comments

Okay, so it doesn’t quite rhyme. But brown fat is rearing it’s head again and this time, it’s the New York Times. I love the New York Times, don’t get me wrong. But the headline of a piece on brown fat, coupled with the information that follows, is a perfect example of raising hopes before dashing them.

Let’s start with the headline:

Feel a Chill? Brown Fat’s Busy Slimming You Down

And the second paragraph:

“It is brown fat, actually brown in color, and its great appeal is that it burns calories like a furnace. A new study finds that one form of it, which is turned on when people get cold, sucks fat out from the rest of the body to fuel itself. Another new study finds that a second form of brown fat can be created from ordinary white fat by exercise.”

Let’s step back and take a look at brown fat. And then I can share the details of the research that the writer is referring to, and where her reporting is a wee bit misleading.

As I wrote about a year or so ago:

In mammals, fat (known among the medical set as “adipose tissue”) comes in two varieties: white and brown.

* White adipose tissue (or “WAT”)  is used for energy storage and to provide warmth. It also protects the organs by acting as a cushion. Most of the fat in our bodies is white.
* Brown adipose tissue (or “BAT”), is mostly found in newborns and tends to diminish as a person ages.  Brown fat is used by the body to regulate temperature and quickly burns sugar to keep infants warm, meaning that exposure to cold activates brown fat cells. This last point may be important when it comes to weight loss.

For decades, brown fat was believed to significantly decline as we grew older, mainly because as we become more able to regulate our body temperatures, we no longer solely rely on biology.  However, PET scanning has shown that healthy adults actually have stores of brown fat  scattered throughout the front and back of the neck and chest areas.

So, is brown fat an equal opportunist? NO!

In fact:

* Women with lean body mass have at least twice the ratio of brown fat compared to men.
* Exposure to temperatures of around 61º F appears to kick off brown fat cell activity, at least in leaner people.
* The higher your body mass index (BMI), the lower the amount of brown fat in your body.

Turning down the thermostat can help lose weight, right?  Well yes. And no.

In controlled situations, volunteers left “chilling” for at least two hours were shown to have a surge in brown fat activity. However, keep in mind that the body is fine-tuned to maintain equilibrium, so, what goes out often goes right back in. In other words, expend more energy, eat more food. And the “chill factor” hasn’t been extensively tested in people under normal, everyday conditions. Still, based on what researchers are able to learn from animal studies, they believe that having as little as 1 to 2 ounces of brown fat in your body could potentially burn about 20% of the average daily caloric intake, that is, if brown fat cells were properly activated.

In the current study (published in the Journal of Clinical Investigation and referred to by New York Times writer Gina Kolata), researchers exposed six men between the ages of 23 to 42 of normal weight, to simulated cold conditions (using a thermal conditioned suit that enabled them to perfuse chilled, 32 degree F water, through it). The men were exposed to the room temperatures for 120 minutes and then cold temperatures for 180 minutes, cold enough to lower skin temperature but not cold enough to induce shivering, which burns calories. During these conditions, the researchers measured the metabolism of the fat using a PET scan. The results? They were able to show for the first time that while metabolism increased by as much as 80% (which is equivalent to around 250 calories burned during exposure to cold for three hours), there were clear differences in results between the men; this suggests that there are individual distinctions in brown fat volume. They also mention in the published study that they cannot exclude how or if other tissues might contribute, tissues that are not captured during the PET scan of this nature, such as the heart and other deep internal organs.

In the second study, which appears in Nature journal, researchers identified a protein in mice that enhances particular gene expression in muscle. In turn, this releases a hormone – iricin – that appears to convert white fat cells into brown cells. If the same were proven true in humans, it might mean that calories burned during exercise was due, at least in part,  to this phenomenon. And if there was a way to enhance it, it might lead to more effective fat burning during exercise.

Notice that there area lot of ‘ifs’ in that sentence.

So, let’s go back to the original statement:

“…brown fat burns calories like a furnace. A new study finds that one form of it, which is turned on when people get cold, sucks fat out from the rest of the body to fuel itself. Another new study finds that a second form of brown fat can be created from ordinary white fat by exercise.”

Yeah, not so fast. When it comes to brown fat, you may want to consider all the facts before you turn down that thermostat and turn up the internal furnace., such as, there’s not enough data…yet.

Not for naught, or nothing.