'Tis the season to pack on the pounds, scientists say

Of all the nutrients the human body absorbs every day, fat has the worst reputation. It is the enemy of dieters, it strikes fear into runway models, and it inspires scammers to sell magic pills promising to destroy it. But burn too much fat at once and you're ridding your body of an organ equal in importance to that of your heart or liver -- and those, says IU biologist Gregory Demas, are organs you definitely cannot live without.\nDemas' studies of the adipose organ, more commonly known as "fat," led him to believe that fat is not only necessary but essential for survival. Stripping the body of the insulation and nutrients it receives from fat is like jogging a mile stark naked on a subzero winter day -- the amount of energy you commit to simply staying warm can knock out other important immune responses. But according to Demas' research, a little bit of fat can help your immune system stay strong. Those extra pounds gained during the holidays might have a real benefit, as he sees it: They could keep you from getting sick this winter.\nBy studying animal models, Demas has found that sudden weight loss leads to the depression of immune function He also has found that the reverse is true -- animals increasing their fat reserves enhance their immune systems. The idea is simple: The more energy, or fat, you have stored, the more you can allocate to different metabolic functions. \n"If your energy reserves are great, then you have the energy to allocate to all sorts of responses," Demas said. \nIn animals, stored energy affects everything from mating behavior to how long animals can fight disease. And though Demas has not studied human fat reserves in his lab, could the same ideas apply? \n"Why not?" Demas said.\nHis theory on the possible connection between fat reserves and the immune system is based on lab work with insects and rodents, particularly the Siberian hamster. The hamsters are ideal for Demas' research because their immune systems change radically from summer into winter. In the summer, the hamsters' immune systems are enhanced when the animals become naturally obese. In the winter, their immune systems are suppressed when the animals naturally become more lean. Demas observed that hamsters that lost weight in the winter decreased their general immunity. To prove this idea, he borrowed a popular human method for rapid weight loss -- and performed rodent liposuction on the hamsters' fatty pads.\nAs he expected, the animals that had fat removed showed signs of repressed immunity. It took 15-20 weeks for the other fatty pads in their bodies to compensate for the loss and bring the hamsters' immunity back up to par. But this result does not necessarily mean a sudden drop in weight makes you automatically susceptible to all sorts of diseases. That question, Demas said, is still wide open.\n"It's as if you can go below some magic threshold and lose immune function," he said. "But where do we draw the line?"\nIt is folk wisdom that cold outdoor temperatures directly cause colds or diseases, as a study called "Exposure to cold environment and rhinovirus common cold: Failure to demonstrate effect" published in the New England Journal of Medicine first showed in the 1960s. But any sort of large environmental or bodily change does affect the immune system. IU Health Center Director Hugh Jessup believes winter is one of the most stressful seasons for the immune system.\nJessup sees students and sports fans out in the cold often improperly dressed or fooling their bodies' skin temperature into feeling falsely warm with alcohol, which causes blood to rush to the skin and eventually causes the body's core temperature to drop. Once the core temperature decreases, the body devotes more energy to keeping itself warm. Even carrying a few extra pounds around the middle might not keep the immune system strong.\n"Taking fat off anytime can be stressful to the immune system," Jessup said. "But what I see most is that if you're improperly dressed (outside), you can definitely compromise your immune system."\nComparatively, everything is stressful to the immune system somehow. But one thing Demas considers is that, in both humans and animals, weight and immune responses change throughout the seasons and according to the age of the individual. Because so many factors affect the immune system, Demas doubts he'll ever run out of questions to test on his hamsters. For himself, Demas said he hardly notices if he is a few pounds heavier in the winter. He figures it may be the healthiest thing for his body.\n"Right now, we'll hop on the scale and expect a steady weight, but humans have natural fluctuations, too," Demas said. "A few extra pounds in the winter or a few less in the summer is no problem, but the virtual absence of fat? That would probably kill you."\n-- Contact Managing Editor Kelly Phillips at kephilli@indiana.edu.