January 24, 2014
News Review From Harvard Medical School -- Could Chillier Homes Help Us Lose Weight?
Recent studies suggest that cooling off to burn more fat is an idea worth exploring, Dutch researchers say. The new report reviews recent human and animal studies. They focus on the activity of "brown fat," which is found in only small amounts in most adults. Brown fat burns calories to help us stay warm in cold temperatures. Shivering increases heat production in people. More recent studies also suggest that the body burns more calories for heat even when exposed to milder cold temperatures. This is called non-shivering thermogenesis. Earlier research by the Dutch team showed that people tend to feel more comfortable over time when exposed to chilly temperatures (about 59 degrees Fahrenheit). The Dutch researchers are planning longer-term experiments that will also track the weight of people who live in cooler environments over time. They also will track the effect of "cold temperature training" on the activity of brown fat. Animal studies have shown that brown fat becomes more active (burns more calories) in a cooler room. The journal Trends in Endocrinology & Metabolism published the new report online. HealthDay News wrote about it January 22.
By Mary Pickett, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Researchers looking for a breakthrough to help fight the obesity epidemic might soon have a new focus: temperature training. In other words, turning down the thermostat might help people lose weight. This has not been proven. Studies done with people have not been long enough to show weight loss over time. But a review of published studies released this week has at least a few obesity experts feeling warm to the idea.
This may take a bit of explanation.
Usually, having extra fat is what makes a person obese. But what if fat could burn calories?
There is such a thing. A small amount of fat in our bodies is named brown fat. This fat is brown because it contains iron-rich energy centers called mitochondria. Mitochondria are like miniature furnaces. Brown fat burns calories in order to help maintain our body heat.
Brown fat is especially abundant (and important) in newborn babies and hibernating animals. But you have some brown fat, too, and you could build more of it. A variety of studies in the last five years have explored the activity of brown fat.
Until recently, we thought brown fat gradually went away after infancy. But researchers recently found that some remains. It's in the upper chest and neck of almost all adults. Brown fat can be seen with an imaging test called a PET (positron emission tomography) scan.
The small amount of brown fat in the body appears to make a big difference in our metabolism. In one study of 24 people, scans of those who were overweight showed much less activity in the brown fat than was seen in people of normal weight. When people in this study were exposed to cooler room temperatures (16 degrees Centigrade or 61 degrees Fahrenheit), the brown fat was more active than at a room temperature of 22°C (about 70°F).
One animal study compared mice kept in cool and warm cages. The mice in the cold could eat more food than the warm mice before they gained weight. The brown fat in the cold mice was seen to be more active, and it burned a large number of calories in the process of generating heat.
Just last year, a study asked 17 people to spend 6 hours of each day in a cold room. The room was 59 degrees, and the study continued for 10 days. By the end of the study, these people had more brown fat. A similar study in Japan resulted in a reduction in total body fat.
Most of us have comfortable, climate-controlled homes and cars. The American lifestyle doesn't build brown fat. This might be one more way that it can contribute to obesity.
What Changes Can I Make Now?
Is your curiosity piqued? Mine is, but I do like to see research that shows real-life results before I get too loyal to a new idea. So far, the studies in people have been small and short-term. They have looked only at indirect measurements, such as the amount or activity of brown fat. They have not recorded weight loss. We need to have long-term studies that randomly assign people to cooler or warmer temperatures to see if there is a bona-fide weight loss advantage to reducing your house or office temperature.
For most of us, the best plan now will be to take no action. We can just watch and wait for more research on this topic.
If you do want to try "temperature training" now, be sure that you do it in a responsible way. Choose a temperature that is cooler than you are used to, but not cold enough to make you shiver or feel uncomfortable. This temperature should be no more than 2 or 3 degrees Fahrenheit lower than what you are used to. You would need to stay with that temperature for weeks or months in order to allow your body to adjust.
Experts say it is hazardous to reduce your home temperature any lower than 63°F, even with "training."
For people who have taken part in these experiments, the response to cooler temperatures has varied. In response to mild cold exposure, most young and middle-aged people in studies showed increases in brown fat activity of a few percentage points to about 30%. For older patients and for some other adults, there was little response.
Please do not try out "temperature training" if you are an older adult or if you have an older adult or a child or teenager in your home.
What Can I Expect Looking to the Future?
For now, all we are sure about is that turning down the thermostat might save you on your energy bills. Researchers are intrigued with the possibility that this also might help people lose weight. Future research on brown fat might provide new treatments that could prevent or treat obesity.