Never Say Diet? : Are All Calories Created Equal?

by Food and Drug Administration (FDA)

(Page 2 of 3)

Set for Life?

This study supports the much-debated "set point" theory, which holds that inner mechanisms set a person's weight at a predetermined level and if anything is done to change the weight, the body will adjust to restore fat content to the set point.

"I regard body temperature, which stays around 98.6 degrees F, to be a set point. Weight doesn't have a set point in that sense," says Xavier Pi-Sunyer, M.D., director of the Obesity Research Center at St. Luke's-Roosevelt Hospital Center in New York.

If there is a set point for weight, it generally seems to move in one direction — that is, the body will not make adjustments to counteract a large weight gain but will fight efforts to lose the weight. "When a person gains weight and stays at that weight a while, the body will defend that weight. It becomes the new 'set point'," explains Pi-Sunyer.

Aside from the action of LPL, the body uses other adaptive mechanisms when food intake is reduced. To cite just two of them: Dieting depresses the metabolic rate so that calories are burned more slowly, and as fat cells shrink, they become more responsive to the action of insulin and do not release their contents as readily.

"The body is very good at defending itself from the danger of underweight, but is not really equipped to handle overweight. Throughout the ages, people have not had a problem with having too much to eat. That's a modern problem," says Pi-Sunyer.

Though a definitive study has yet to be done in humans showing that weight gain becomes more likely after each successive diet (the so-called "yo-yo" syndrome), the Cedars-Sinai study strengthens this controversial hypothesis. However, in order to show conclusively that weight loss gets harder each time a person loses and regains weight, the subjects in the Cedars-Sinai study would have to be followed through several cycles of weight gain and loss to determine whether LPL levels kept rising after each diet.

Repeatedly losing and gaining weight may have other health consequences, according to a report in the June 27, 1991, New England Journal of Medicine. American and Swedish researchers analyzed weight fluctuations and later health problems over a period of 32 years in more than 3,000 women and men who participated in the Framingham (Mass.) Health Study. The researchers said that people who repeatedly lose and regain weight appear to have an overall higher death rate and to be at greater risk of heart disease and some cancers than those whose weight remains stable (even if overweight) or steadily increases.

Are All Calories Created Equal?

"The body will do what it was programmed to do even if that's not what you want it to do," notes Callaway. For this reason, restricting food intake to 1,000 or 1,200 calories in order to lose weight is "doomed to failure," he says. "For many people, going on one more diet isn't going to solve a weight problem in the long run."

Even well-established weight loss programs are not individualized enough to account for genetics, past dieting attempts, and a person's activity level, he says.

While Pi-Sunyer agrees that putting everyone on the same prepackaged weight-loss regimen can be counterproductive, he believes that restricting caloric intake is an important weight-control tool. "You can easily cut caloric intake just by restricting the amount of fat and sugar you eat. This might be the only adjustment a moderately overweight person would need to make in order to lose weight."

Research indicates that obesity may be linked to the proportion of fat in the diet rather than to the amount of calories consumed, according to a survey of the diets and exercise habits of 107 men and 109 women reported in the September 1990 issue of American Journal of Clinical Nutrition. Researchers at Indiana University in Bloomington found that overweight subjects got 35 percent of their calories from fat and 46 percent from carbohydrates, compared to 29 percent of calories from fat and 53 percent from carbohydrates for their slender counterparts. A recent University of Vermont study suggests that limiting fat intake to about 20 percent of total calories enabled chronically obese patients who failed to lose weight on a variety of reducing programs to lose an average of 20 to 30 pounds over the course of a year.

Scientists used to think that all calories were created equal. That is, whether it came from fat, carbohydrates or protein, a calorie produced a certain amount of heat when the body burned it to fuel metabolic processes. Thus, according to "The Dieter's Law of Thermodynamics," mashed potatoes and milkshakes were no more culpable in promoting weight gain than pasta and peas — as long as caloric intake was limited to 1,000 or some other magic number.

Alas, further research has shown this to be an illusion. Calories from carbohydrates, fat and protein are used differently by the body. Virtually all fat calories are immediately stored in fat cells. Carbohydrates and protein are converted into glucose for fuel, with only those calories in excess of the body's energy needs being stored.

Compounding the problem, a gram of fat has 9 calories while an equal amount of carbohydrates or protein has 4. "For the same number of calories, a person can have a much bigger serving of a food that is primarily carbohydrate as one that is high in fat," observes Walter Glinsmann, M.D., associate director for clinical nutrition at the Food and Drug Administration's Center for Food Safety and Applied Nutrition. For instance, a 6.5-ounce baked potato has the same number of calories as 1.5 ounces of potato chips (about 225).

The type of fat in the diet is important as well. Currently, the National Cholesterol Education Program recommends that the diet be limited to 30 percent of calories from fat, with no more than 10 percent of those coming from saturated fats. "Unsaturated fats are precursors of such biologically active molecules as prostaglandins, which are involved in a variety of body processes, including blood pressure regulation and immune system function. Various types of fat have different roles in health maintenance and disease risk," says Glinsmann.

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