Want to lose a pound or more a week without really trying? It sounds too good to be true, but new research suggests it may be possible by making small changes in your diet.

The key: replacing some of the high-calorie foods you eat with fruits, vegetables, and other water-dense foods that keep you just as full. Young women taking part in a Pennsylvania State University study ate a whopping 800 fewer calories a day and never missed them when this eating approach was combined with a 25 percent reduction in overall portion size.

The study was presented by nutrition researcher Barbara Rolls, PhD, at the annual meeting of the North American Association for the Study of Obesity in Las Vegas. Rolls’ book The Volumetrics Eating Plan explains the approach and she will publish a cookbook and lifestyle guide based on it early next spring.

“I am not a great advocate of simply telling people to eat less, because they are going to get hungry if they do that,” she tells WebMD. “What we are trying to do is give people satisfying amounts of food that are less [calorie] dense.”

High-Volume Eating

The rationale behind “volumetrics” eating, Rolls explains, is that people tend to eat the same volume of food each day, regardless of the calories. So adding vegetables to that pizza, lasagna, or casserole will increase the food’s volume, and result in fewer overall calories consumed when portion-sizes stay the same.

But you can’t go too low with fat and protein. As anyone who has tried to lose weight on a rabbit diet can tell you, a 12-ounce head of lettuce and a 12-ounce T-bone steak are not created equal when it comes to satisfying hunger. Rolls recommends that between 20 percent and 30 percent of daily calories come from fat.

The Penn State study included 24 women between the ages of 19 and 35 whose food intake was strictly controlled for two consecutive days each week over the course of four weeks. Some of the women ate a diet consisting of approximately 2,400 calories a day, while the other women took in approximately 1,600 calories, eating similar foods that were modified to add vegetables and fruits and reduce fat and sugar. Portion sizes were also reduced by 25 percent.

Reducing the calorie density of foods was associated with a 23 percent decrease in calories eaten per day, while decreasing portion sizes lowered overall calories by 12 percent. And the calorie reduction was found to be the same on day two as day one, suggesting that the women were not compensating for eating less by eating more later on.

Although weight loss was not considered in the study, the reduction of 800 calories per day likely would result in a weight loss of about a pound and a half over the course of a week.

“These women were satisfied with the amount of food they were eating, and their diets were healthier too,” Rolls says.

Sound, But No Magic Bullet

Dietitian Elisabetta Politi, RD, says the principles behind the Penn State eating plan are sound, but she adds that the approach does not appear to be a magic bullet for weight loss.

“Unfortunately, the foods that we are exposed to tend to be very calorie-dense,” she says. “So while this approach works well in a controlled situation, it is not as easy to follow in the real world where the temptations are so great.”

Rolls agrees, adding that the food industry is a big target of her latest research.

“Small changes in energy density and/or portion size can add up to big changes in the long run for consumers,” she says. “People are going to eat the portions that are put in front of them. But we showed that you can make foods healthier and reduce calories and the changes won’t be noticed.”

By Salynn Boyles, reviewed by Michael W. Smith, MD

SOURCES: Presentation to the North American Association for the Study of Obesity, Nov. 14 in Las Vegas. Barbara J. Rolls, PhD, Gutherie Chair in nutrition, Pennsylvania State University, Pittsburgh. Elisabetta Politi, RD, nutrition manager, Diet and Fitness Center, Duke University, Durham, N.C.