”Eat all you want and lose weight.”
It sounds like an ad on late-night television, and such an obvious overstatement might make readers shake their heads in disbelief,
disappointment and disgust.
But there is truth behind the statement, along with a few caveats.
Nutritionists at Cornell University have come up with some convincing evidence that you can lose weight without calorie restrictions, without bird- sized portions.
Their findings, reported in the May issue of the American Journal of Clinical Nutrition, resulted from an 11-week study that a Cornell spokesman said is ”the longest controlled human-feeding study ever undertaken.”
The chief investigator, David Levitsky, professor of nutrition and psychology at Cornell, had one goal when he shaped the study: to prove that people can change their body weight, that the set point theory, which links weight to genetics, is full of holes.
It would be nice if he could show that genetics is not entirely responsible for one`s weight.
Purpose of the study
”One of the major reasons for doing the study,” Levitsky said in a telephone interview, ”is to attack the currently held notion of a set point. That`s pretty depressing because it means you can`t change.”
The set point theory maintains that your weight is held fairly constant by physiological and biological conditions and that as you start to lose weight the body catches on and you increase the amount of food eaten or your metabolism rate drops.
But Levitsky contended that if you reduced the fat in your diet, not the carbohydrates, you would not increase the amount of food you ate and your metabolism rate would not drop.
He also said that genetics was not entirely to blame for weight. ”There are environmental determinants of your weight,” he said. ”Maybe you can change your weight by 10 to 15 percent by changing your diet. Maybe you can change it even more.”
He believes his study has proved both points: that you can tell your genes to get lost and you can toss out the set point theory.
Thirteen active and slightly overweight women between the ages of 22 and 56 were randomly assigned a low-fat diet (20 to 25 percent of calories from fat) or a control diet (35 to 40 percent of calories from fat), the normal American eating pattern, for 11 weeks. This was followed by a break of seven weeks and then the conditions were reversed for another 11 weeks.
The subjects on the control diet ate 2,000 to 2,200 calories a day; the low-fat subjects ate about 250 fewer calories, even though they could eat as much as they wanted.
Only fat differed
The foods were the same; only the fat content was different. The low-fat group and the control group ate a turkey sandwich and blueberry yogurt for lunch on Monday, but the control group had a turkey sandwich with mayonnaise and regular yogurt while the low-fat group had a turkey sandwich without mayonnaise and nonfat yogurt. By the end of the 11 weeks, the low-fat dieters had lost twice as much weight as the control group.
Now for the caveats.
1. The average weight loss in the low-fat diet group was about a half-pound a week, not what late-night ads might promise.
2. The difference in energy, or caloric, intake between the low-fat and control groups was 250 calories at the beginning of the study; by the end, the difference was 200 to 220 calories.
In other words, the daily intake of calories on the low-fat diet did increase over time for unexplained reasons, but it was still well below the intake of the control group.
3. Because the study lasted only 11 weeks, no conclusions can be drawn about long-term weight loss. If someone stayed on the low-fat diet for six months, would the caloric intake gradually return to the level of the traditional American eating pattern in which fat accounts for 35 to 40 percent of calories?
The study, Levitsky said, did not answer all questions the researchers had hoped would be settled. In an ordinary weight-loss diet-one in which calories are reduced with no thought to whether they come from fat, carbohydrates or protein-there is a classic weight loss curve. The greatest loss of weight takes place at the beginning of the diet, gradually trailing off. That did not happen in the low-fat diet.
Levitsky explained that in such a traditional diet, ”One of the major reasons for the slowing of weight loss is the slowing of the metabolic rate. We did not see that, but we are not sure why. There is evidence that the metabolic rate may be related to carbohydrates, not fat, and carbohydrates were not decreased in the low-fat diet. Some scientists suggest that the metabolic rate is determined, in part, by carbohydrate intake.”
To answer unresolved issues, Levitsky will conduct a six-month study as soon as he gets financing.
