Fats Beget Fat. So Next Time You`re Famished, Load Up On Carbohydrates.

May 07, 1986|By Robert Bennett. (copyright) 1986 American Health Magazine- Washington Post Writers Group.

A calorie is no longer just a calorie. At least, not when it comes from fat.

In studies that challenge decades of accepted wisdom about caloric intake and weight control, scientists are finding that calories from fat are uniquely fattening. Eat a fat-rich dessert such as premium ice cream, and you will, as the saying goes, apply it directly to your thighs.

But replace fat in your diet with carbohydrates, and it`ll be easier to maintain your weight. Even if you occasionally eat a little more than you really need, your body will have a hard time turning the excess carbohydrates into body fat. Calories from protein and carbohydrates even speed up metabolism and thus help in maintaining weight.

Of course, many dieters already try to avoid fatty foods, but now they have a much more powerful reason to do so. The old rationale was simple: An ounce of fat contains more calories than an ounce of carbohydrate--it`s a more concentrated source of energy. And if you take in more caloric energy than you burn, the theory goes, you`ll gain weight.

But the new research says more: It says fat provides energy in the form your body most readily stores on your thighs, hips or wherever. The energy in bread or pasta, in contrast, is stored only in small amounts in the muscles and liver, and, under normal conditions, is almost never turned into body fat. CARBO LOADING

No one is saying, of course, that we can eat unlimited carbohydrates and never get fat. For health, we`re also better off with complex carbohydrates, such as vegetables, grains and beans, than foods packed with sugar. And recent diet-cancer research suggests excess calories, from whatever source, may promote tumor growth. But if you watch your calories, exercise and eat a low- fat, high-carbohydrate diet, you`ll stand a good chance of getting lean and staying healthy.

The new theories fit what farmers, and even some diet gurus, have known for years. ``Any pig farmer knows that you can`t get pigs fat feeding them wheat; you need corn, which contains more oil,`` says professor of medicine Eliot Danforth, whose studies of obese patients at the University of Vermont contributed to the new findings.

The same principle applies to people.

Danforth first learned this a decade ago, a few years after he joined an obesity research project headed by Dr. Ethan Allen Sims. To study the effects of obesity, the researchers tried to fatten male prisoners who had volunteered for a study of overfeeding.

It was surprisingly difficult to get them all to gain weight and keep them fat, a finding that other researchers use to support the ``setpoint``

theory of weight control. That theory holds that each individual maintains weight within a fairly narrow range over the long haul, whether you diet or overeat (though different people are ``set`` differently). If you diet, the body will compensate by burning fewer calories and increasing your hunger;

overeat, and the body burns more, helping to maintain a ``set`` weight.


But Sims, Danforth and their team stumbled on another surprise: All overeating is not alike. Prisoners on a high-fat diet gained weight more easily than those on a low-fat, high-carbohydrate diet.

That got other biochemists wondering. Metabolic theory at the time held that our bodies transform excess carbohydrate calories into a significant amount of body fat. But it turned out that ``the fear that carbohydrate turns into fat is unfounded,`` says Jean-Pierre Flatt, professor of biochemistry at the University of Massachusetts Medical Center in Worcester, who`s done dietary studies both in people and in animals.

One reason has to do with metabolic efficiency. Since dietary fat is already fat, it`s easy to add it to fat stores in the body. To turn 100 calories of a pure fat like butter into body fat ``costs``only about 3 percent, or 3 calories. The rest--97 calories--end up in your fat cells.

But to turn carbohydrate to fat is much more complicated. The body has to make a series of intermediate compounds along the way, and many of these steps cost energy. As a result, Flatt calculates, to turn 100 calories of carbohydrate into fat ``costs`` about 23 percent, or 23 calories. In effect, if all of the carbohydrate were to be made into fat, which rarely happens, 100 calories of carbohydrate would be ``worth`` only about 77 calories.

Much of the new work is still speculative, of course, including the very existence of a setpoint--a biologically set weight. But ``if a setpoint exists, you can presumably lower it by increasing the ratio of carbohydrates to fat,`` Flatt says. Exercise, of course, helps, too. --