Imagine adding a super-sized course to your meal that actually trims calories from the bottom line. You probably think it’s too good to be true.

Wrong again.

Findings presented this week by Pennsylvania State University researchers at the annual meeting of the North American Association for the Study of Obesity found that starting lunch with a healthy salad reduced the total calories people consumed in the meal. The seven-week study of 42 people found that participants who ate three cups of low-calorie salad as a first course wound up eating fewer calories at the meal than those who skipped the salad.

“The findings are surprising because usually adding variety to a meal by adding an extra course tends to make people eat more,” said Barbara Rolls, professor of nutrition at Penn State and lead author of the study.

Here’s how to apply these results to daily life:

• Keep it low-fat. The study looked at six salads varying in size, calories and fat. The lowest-fat salads — those with 14 percent of calories from fat — worked best at reducing overall food consumption.
• Size matters. In the study, larger salads were better than smaller ones at shaving calories from the meal. Eating three cups of low-fat salads resulted in a 12 percent overall reduction in lunch calories compared with 7 percent fewer calories for those who ate 1 1/2 cups of salad. Best (and most surprising) news: Participants felt equally full on three cups of salad, whether it contained 100 or 400 calories.
• Watch the tipping point. The study found that a salad of about 100 calories had the most effect at reducing overall calories for the meal. As calories crept to 200, with moderate fat, there was either no change in total meal calorie consumption or a slight increase in calories. High-fat salads of 200 calories or more actually resulted in higher total calories at lunch, up to 145 more. That’s another reason, Rolls says, to load up on the low-cal veggies — and not the cheese and (high-fat) dressing.
• Pile on the greens. They’re filled with flavor, water, fiber and plenty of phytonutrients, minerals and vitamins and have about five calories per cup. Plus, three cups of greens provide three of the five to nine servings per day of fruit and vegetables recommended by the National Cancer Institute. In the study, salads were made of Romaine and iceberg lettuce, carrots, tomatoes, celery and cucumbers (as well as small amounts of cheese and dressing). But any combination of greens and other water-filled vegetables will likely do. “The bigger the vegetable volume, the bigger the impact of this first course,” Rolls says.
• Savor the flavor. Participants in the study got 20 minutes to eat their first-course salads — more than many people take to eat their entire lunch at their desks. Research suggests that eating slowly gives your stomach time to send satiety signals to the brain.
• Ask for the dressing on the side. That puts portion control in your court, not the restaurant’s. Study participants got one to three tablespoons of dressing on their salads — far less than most restaurants slather on — yet they still reported feeling full afterward. “The fullness wasn’t affected by the calories, only by the portion,” Rolls says.
• Go ahead, try the low-fat dressing and cheese. While taste has driven a lot of consumers away from low-calorie or low-fat dressings, the Penn State study found that participants had trouble detecting the reduced-fat dressings. “The low-fat products have just gotten much better in taste,” Rolls says.
• Avoid the croutons. That’s because they tend to be high in calories. And they’re missing the water found in the greens and other vegetables, so they’re less likely to fill you up. “What I like about what McDonald’s has done with their salads is that they’ve put croutons and dressing in separate packets and given consumers choices about ordering grilled or fried chicken for their salads,” Rolls says.