updated 10/7/2005 8:32:33 AM ET 2005-10-07T12:32:33

People often bemoan, “Why is it so easy to gain weight, but so hard to lose it?” Cornell University professor David Levitsky contends that we often get in the way of our bodies’ natural ability to bring us back to a healthy weight.

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His research shows that after a period of overeating, if we simply go back to a diet that supports a healthy weight, our bodies will increase the rate at which we burn calories and we will gradually lose weight.

In one of his studies, a group of normal-weight men and women were asked to dramatically increase their calorie consumption for two weeks. Not surprisingly, they gained weight. But when they returned to their regular eating habits, their weight gradually decreased without extra exercise or severe cutbacks in the amount of food they ate.

Dr. Levitsky points to a variety of human and animal studies that show how a metabolic rate increase could explain this weight loss. The increase in metabolism is greater once a person returns to normal eating habits than during the period of overeating.

If our metabolism can speed up, why do so many people have trouble losing weight? Dr. Levitsky suggests that people still eat more than they need, or they cut back too much.

Why is it counterproductive to cut calories too much? First, when we make changes that are too big or too challenging, we usually can’t stick with them long enough to be successful. Second, dramatic cuts in calorie consumption can decrease our metabolic rate, slowing down calorie burning.

Dr. Levitsky’s study also supports the wide body of research that identifies “environmental cues” – especially portion size – as more influential over how much we eat than our actual physical hunger. When small amounts of overeating lead to a gradual weight gain over years, Dr. Levitsky suggests that people are stuck in certain eating habits and don’t realize how much their intake exceeds their needs. According to him, the way people respond to environmental cues determines their weight.

A variety of cues can cause us to eat more than we need. In studies involving people of all ages and weights, the more food that was available to people, whether on their plate or in a serving bowl, the more people ate. People are so unaware of this overeating that they don’t feel any difference in fullness after eating very different amounts of food. Many people could probably eat less without feeling hungry.

Be patient
Another reason we can unintentionally overeat is called “caloric density.” The same quantity of food can vary widely in calories. For example, one-half cup of meat has more calories than one-half cup of vegetables. If people paid attention to their sense of fullness, they’d eat smaller amounts of high-calorie foods, but studies show that people don’t.

We may also overeat because of social or emotional cues. The timing of our eating and the hunger-satisfying power of the foods we choose may also influence how much we eat.

If you’ve gained weight, advises Dr. Levitsky, trim about 200 to 250 calories from your daily food choices. To do this, you can slightly reduce all of your food portions throughout the day, or eat less of one or two higher-calorie foods. You can even cut calories without eating less food by shifting the proportions of what you eat. Choose more low-calorie foods like vegetables and cut back on the high-calorie items. The New American Plate, a healthy eating strategy developed by the American Institute for Cancer Research, combines these two ideas of portion size and proportion of foods into one approach.

Once you’ve taken up this strategy, exercise patience. In Dr. Levitsky’s study, people overate for two weeks, but they took more than three weeks to lose the weight they gained. Stick with the modest cutbacks and you should see results eventually.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

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