Losing weight may be as simple as eating more - eating more fruits and vegetables and less food that is “calorie-dense,” such as cheese, researchers said on Wednesday.

Dieters who were told to eat foods that fill you up with water and fiber, such as vegetables and fruits, lost weight without counting calories and without gimmicks, a team at Pennsylvania State University found.

A second study looking at what people normally eat found that those who eat more fruits and vegetables tend to weigh less.

Both studies were presented this week at a meeting of the North American Association for the Study of Obesity in Las Vegas.

“In one of the studies, we looked at the eating patterns of 7,500 men and women who constituted a representative sample of American adults,” said Dr. Barbara Rolls, a nutritionist who directed both studies.

“In the other study, 101 obese women were counseled to increase their intake of water-rich foods and to select reduced-fat foods rather than full-fat ones. In both cases, eating more low-energy-dense, water-rich foods, such as fruits and vegetables, was associated with lower body weights,” Rolls said in a statement.

Rolls said these are the first large studies to demonstrate scientifically what common sense dictates - fill up on less-fattening foods and lose weight.

Groups such as the American Heart Association have long advocated eating more fruits and vegetables and eating less calorie-laden food such as meat, cheese and sweets. The approach also underlies diets such as Weight Watchers.

Several recent studies have shown that while diets, such as high-protein regimens, can help weight loss, the effects are short-term.

The Penn State team studied 7,500 typical Americans interviewed in the U.S. Department of Agriculture Continuing Survey of Food Intakes by Individuals.

Those who ate more “low energy dense” foods ate more food, by weight, than people who ate calorie-dense foods. But they ate fewer calories.

For the second study Julie Ello-Martin divided 101 obese women into two groups. One group was asked to eat more water-rich foods and to choose fat-reduced foods, while the other was put on a stricter diet focused on cutting portion size and fat.

After the first six months, the women told to fill up on vegetables had lost an average of 21 pounds while the women on the stricter diet had lost only 15 pounds, Ello-Martin found.

“This is the first long-term study to look at how a low energy density diet can affect body weight. It’s important because it shows that a healthy diet pattern can result in significant weight loss without counting calories or fat grams,” Ello-Martin said.