Preventive Medicine Column
Dr. David L. Katz
Brown fat is hot. It is the focus of two recent research papers, one in mice and one in men, and the marquee item in a recent New York Times Article. Brown fat is hot, because it may help keep us warm, burn calories, and help keep us thin.
But how hot is it? Proverbs tell us where there’s smoke like this, there’s fire. But sometimes where there’s smoke, there’s just smoke- and a whole lot of hot air!
That was my impression when brown fat first started heating up in 2009. In the April 9th issue of the New England Journal of Medicine that year, three articles and an editorial highlighted the potential and apparently overlooked importance of brown fat in human weight regulation.
The New York Times jumped on the brown fat band-wagon then, suggesting that these “new” findings might offer a ‘cool way to lose weight‘- namely, by using some yet-to-be-discovered wonder drug to reset the human thermostat. Or, in the interim- turning down the thermostat in our homes.
The heat has been turned up rather than down on the topic, however, with the advent of the two new brown fat studies. One, in mice, published in the prestigious journal Nature, purports to establish the existence of a new hormone, irisin, which is integral- in exercising mice, at least- to the process of converting garden-variety white fat into its hottie counterpart, brown fat. Irisin exists in humans as well as in rodents.
If irisin does in people just what it does in mice, and if we can develop irisin to give people, it might cause them to burn more calories without needing to exercise. Of course, amphetamines do that already- and they’re not really a terrific idea. But I don’t want to get ahead of myself.
The second new study, demonstrated in 6 healthy men that cold can induce brown fat to burn white fat. Body temperature is maintained with cold exposure by the combustion of the body’s stored fuel (i.e., white fat) by the body’s newly discovered stove (i.e., brown fat). If the body gets even colder, shivering ensues- and the muscle activity of shivering helps restore a normal temperature. Only when all of these defenses are overcome does hypothermia occur.
The new study was also noteworthy for the magnitude of the observed effect. By making the participants cold up to but not past the point of shivering, metabolic rate was reportedly increased by some 80%- resulting in the expenditure of an extra 250 calories or so over 3 hours. That’s not an unimpressive figure- but a brisk walk for one hour would do the same.
That’s why brown fat- or at least brown fat combined with cold- is hot.
One opportunity to which this research points is weight management by toughing out the cold. But being cold all the time is in, a word, uncomfortable. If people were willing to be uncomfortable to control weight, a whole lot more of us would exercise!
The second opportunity- related in particular to the mouse study- is to increase the generation of calorie-burning brown fat by exercising. But this is really just another way of saying if you exercise more, you are apt to weigh less- and almost certain to be healthier. Those arguments haven’t carried the day with most members of our population thus far, and it’s not obvious that the added bonus of “and you’ll have a bit more brown fat, too” will clinch the deal.
Which brings us to the last great opportunity: a new wonder drug. Irisin, or something like it, in a capsule or syringe.
We have numerous, intricate, overlapping layers of metabolic defense against starvation- the threat that has stalked the heels of Homo sapiens from time immemorial. An effort to use a drug- any drug- to rework the fundamentals of human metabolism so that we don’t turn a surplus of calories into an energy reserve in burgeoning adipose tissue seems to me an enterprise fraught with peril. I don’t believe we will ever devise such a drug- and if ever we do, I shudder to think what its unintended consequences may be.
Like everyone else, I hope the new studies of brown fat provide insights we may eventually exploit to improve the human condition. But while a bit less inclined to give the whole topic the cold shoulder than I was in 2009, I am cool on the concept of weight control through pharmacology. I contend, as I always have, that we will win or lose the war of weight control with our feet and our forks- not pharmacotherapy. So stay tuned to the smoke signals about brown fat. But I urge you to keep other irons in the fire.
Dr. David L. Katz; www.davidkatzmd.com