Fat is not just fat. There is white fat, which accumulates energy and makes people gain weight, and brown fat, which burns energy and helps people lose weight. Researchers have long sought a method to convert white fat into brown fat. Now they may have found it.

  Fat deposits around the waist and hips are particularly detrimental to the heart’s health, but researchers may have found a way to activate “wonder cells,” or brown fat cells, which are not only found in children and young people but also in adults, contrary to what was once believed.

  A direct connection between brown fat cells and weight loss among over- weight humans has not yet been proven, but scientists have reduced the body weight of mice in experiments with the cells. Consequently, a whole new medical research strategy aims to increase human energy consumption instead of focusing exclusively on diet and exercise.

  TWO TYPES OF CELLS

  White fat cells store fat that’s absorbed through food, creating a reserve of energy available for use during physical exertion. In the Western world, however, humans are much more sedentary than they have been historically, spending much Cold exposure of the day gazing at computer screens. White fat cells wait in vain to release that stored energy into the body and remain as unburned fat in the meantime, in rolls around the waist and hips and as deposits in the buttocks and thighs.

  Brown fat cells behave very differently. In adults, they sit in small clusters over the collarbones and along the spine — and occasionally between white fat cells, scientists have discovered. The cells were first found in human infants and hibernating animals, which use them to produce heat when cold. Metabolic expert Stephan Herzig of the German Cancer Research Center in Heidelberg says the brown fat cells do not store fat in the traditional sense; rather, they consume the fat of the white cells by “firing the energy through the chimney.” The heavy concentration of mitochondria, the cell powerhouses that contain high levels of iron, give the cells their brown tint.

  The body’s amount of brown fat, however, decreases in human beings as they age, less so in men who remain slim and more so in men who become overweight. Researchers don’t yet know the ratio of brown fat to white fat in adults, but its mere presence is not enough to produce a slimming effect. Researchers estimate that less than 2 ounces of brown fat, if activated, could account for one-fifth of the energy an adult burns daily. Thus, scientists are working to convert white fat into brown fat to make use of the small powerhouses.

  Wouter van Marken Lichtenbelt of the Maastricht University Medical Center in the Netherlands has postulated that cold air could help move the process along. In an experiment involving normal-weight, overweight and obese men, there was no activity in the brown fat at 72 degrees. But two hours in a room with a temperature of 60 degrees seemed to kick the brown fat cells into a higher gear, although the tendency was significantly weaker in the overweight and obese men. Van Marken Lichtenbelt is hopeful about the future of the study. “We are able to activate brown fat in overweight people,” he says, “so perhaps it can help to solve the global obesity problem.”

  In another ongoing study, a team of scientists led by professor Leslie Kozak of the Pennington Biomedical Research Center in the United States is subjecting normal-weight men to daily, 15-minute cold shocks for one week. Results have shown that some of the men produce more heat even at normal room temperatures, perhaps due to brown fat, though that is still an unproven hypothesis.

  Van Marken Lichtenbelt has no plans yet to prescribe daily swims in freezing swimming pools for weight loss, but thinks intelligent temperature regulation of offices and homes could be beneficial. “Cool is cold enough to get the brown fat cells activated,” he says.

  Other researchers, such as Herzig, are investigating long-term medical treatment with the aim of provoking a forced reaction to cold in the body even at comfortable temperatures. He and his colleagues have manipulated mice genetically to produce more of the hormone prostaglandin, which makes something similar to brown fat appear in the middle of the white fat — so-called beige fat. It’s similar in composition to brown fat but is generated in a different way, and it causes the mice to lose weight.

  Ultimately, research is focusing on what happens at the molecular level when white fat becomes brown fat or when scientists succeed in activating existing brown fat; the aim is to develop new drugs that have the same effect. Another possibility would be to create brown fat cells using stem cells and inject those fat cells under the skin. The method has been successfully tested in mice but not yet in humans.