Investigators found that people who were served three cups of a salad, totaling 100 calories, ate 12 percent fewer calories overall than people who did not eat a salad at the start of their meals.

Study author Dr. Barbara J. Rolls explained that previous research has shown that eating low-calorie but filling foods -- such as fruit, broth-based soups and salad -- can reduce the amount of food people eat during the rest of the meal.

"Because you're full at the start of a meal, you eat less later," she told Reuters Health.

Importantly, only low-calorie starters appear to produce this effect, Rolls noted. In this study, for instance, when people ate a 400-calorie salad that contained high-fat dressing and cheese, they consumed 17 percent more during the entire meal than if they did not eat a salad at all.

Rolls noted that people need to include a small amount of fat in their salads to absorb the important nutrients, but they should try to limit the calorie content to between 100 and 150 calories.

As reported in the Journal of the American Dietetic Association, Rolls and her colleagues asked 42 women to eat one of 6 different types of salads before a pasta lunch, or no salad at all. The researchers then measured how many calories they consumed throughout the entire meal.

None of the women participating in the research were trying to gain or lose weight.

The researchers found that women who ate 1-1/2 cups of salad (50 calories) ate 7 percent less during their meal than when they did not have a salad. Eating 3 cups of salad (100 calories) decreased meal intake by 12 percent.

Rolls noted that salad-eaters likely stop eating their main course earlier than they would otherwise because they believe they have eaten a lot of food, despite the fact that their salad contains fewer calories than the main course. In addition, the salad requires a lot of chewing, adding time to the meal, and again reinforcing the idea they have eaten enough, she said.

Also, portion size seemed to matter in this experiment. When people were offered 100 calories' worth of salad in two different portions -- 1-1/2 cups and 3 cups -- they ate less during the main course after the larger portion, suggesting "the bigger, the better," Rolls noted.

"It's a whole sequence of cues, basically all leading you to think you've eaten more," said the researcher, based at Pennsylvania State University in University Park.

"The implication of this study is that when selecting a first course, consumers should be aware that both the energy density and the portion size of the food affect the amount of energy they consume in the meal," Rolls and her team write.