The main reason some people get fat isn't because of genetics or how much they eat, said a Cornell University obesity researcher. It's because, compared with thinner people, they snack more often during the day and move about a lot less.

The best way to slash the country's skyrocketing medical costs associated with obesity is not through dieting but by persuading people to exercise more, said David Levitsky, professor of nutritional sciences at Cornell. The government should take a more aggressive role in ensuring employers offer workers more opportunities to stretch their legs and exercise and provide more non-competitive sports for children as well as after-school programs in inner-city neighborhoods where children often can't play outside safely, he said.

"And forget dieting; it just doesn't work," according to Levitsky.

When people are not allowed snacks, they still eat about as much at mealtime as when they do snack. And people who skip a meal or don't snack do not compensate at the next meal by eating more. That means that the less often you eat, the fewer calories you consume, he explains.

America, he says, needs to slow the trend of adults and children becoming fatter, and to achieve this goal, Levitsky offers the following messages:

— "The popular high-protein, low-carbohydrate diets are just gimmicks," he says. They work temporarily because they consist of fewer calories, but the weight comes right back because the diets are nearly impossible to stay on indefinitely. Such diets, on a long-term basis, could be linked to higher risks of cancer, heart disease and kidney failure, he said.

— "The ideal weight charts send the wrong message to consumers; it's not your weight that counts but what goes into your weight." In other words, what's much more important to health are indicators such as blood pressure and cholesterol and healthful lifestyle habits, such as a low-fat diet and plenty of exercise. "Recent studies show shorter mortality is more related to inactivity than to body weight."

— What you weigh matters to your life, though. Studies show obese people experience discrimination in jobs, housing, education, dating and marriage.

— The popular set-point theory — that your body regulates your appetite and body weight — seems to be losing ground as new research fails to support it.

— Americans are getting fatter because they are consuming about 1,000 calories more each year than the previous year. That is less than 10 calories a day. To burn off that extra energy, the average person needs only to walk or clean house about 17 hours more a year, power walk, bike or dance about eight hours more or engage in vigorous exercise (walk uphill, play basketball or jump rope) about three more hours a year.

— The benefits of exercise include not only more calorie expenditure, but also low cholesterol levels, greater muscle mass (which uses more calories for fuel than fat cells do), smaller fat (adipose) cells and changes in brain chemistry that induce feelings of well-being and a greater sense of control over one' life.

— Levitsky's final advice on the best way to control weight it to "Move your body whenever possible while reducing calories from fat. Eat only when you have to, which means at meals and finally, accept your body size. Be happy even if you think you're not thin. The major problem with body size is on the outside — from society and the media — not within you. Take back the control about food and body size."

For more information about Levitsky's views in high-protein diets, visit: www.human.cornell.edu/faculty/facultybio.cfm?netid=dal4&facs=1.