Published March 04, 2011
NEW YORK – Adding pureed vegetables to entrees reduces the number of calories the meals pack without sacrificing texture or taste, according to Pennsylvania State University researchers who tried it on unsuspecting study subjects.
Using "stealth vegetables" to pad dishes provided a double-helping of dietary benefit, the University Park group reports, because some of the participants more than doubled their intake of fiber- and vitamin-packed veggies - without even knowing it.
The study included 20 men and 21 women who agreed to eat at a laboratory once a week for 3 weeks. The meals were always the same: carrot bread for breakfast, macaroni and cheese for lunch and chicken-and-rice casserole for dinner. Volunteers were served as much as they wanted to eat, along with side dishes like bread rolls, strawberry yogurt, broccoli and green beans, depending on the meal. They also were given snacks to take home for the evening, such as carrot sticks and fig cookies.
Portion sizes were strictly controlled by weight and the researchers kept a close account of the amount of food participants ate.
Unknown to the diners, back in the kitchen, cooks were adding vegetables that had been steamed then pureed-cauliflower, squash or carrots, depending on the entree-to some of the main dishes. The result was a helping of food that, although it looked, tasted and otherwise resembled the original, was either 15 percent or 25 percent vegetable puree by weight. Some participants got the traditional version of the entrees with no hidden veggies.
Vegetables have fewer calories, ounce for ounce, than the ingredients they replaced, so volunteers eating the doctored entrees were "still getting the same weight of food, but the calorie content is less," said Alexandria Blatt, a doctoral student in nutritional sciences who helped conduct the research.
The imposter ingredients did not seem to faze the study subjects, who all ate about the same amount of a given entree regardless of how much puree, if any, it contained. As a result, the researchers say, the subjects' calorie intake dropped substantially when they were consuming the altered foods -- by as much as 360 calories a day when the entrees consisted of 25 percent puree. Meanwhile, the subjects' vegetable intake rose by up to two servings a day, a substantial improvement over the typical American diet.
By cutting back 360 calories every day, a person could lose one pound of body fat in about 10 days.
Although nearly half the participants said at the end of the study that they could tell something was different about the doctored meals, only two said they could taste the extra vegetables.
"Everybody thought it looked great, tasted great," Blatt told Reuters Health in a telephone interview.
In a real kitchen where eaters don't need to be tricked with adulterated meals, cooks would have more flexibility about which vegetables they could incorporate into foods, and how much of them, Blatt said. "In the laboratory, you have to really formulate your recipes to prevent people from being able to identify the one entree that has hidden vegetables."
Richard Mattes, professor of foods and nutrition at Purdue University in West Lafayette, Indiana, said promoting consumption of fruits and vegetables is "highly desirable," but added that they are far from a panacea for weight loss.
Mattes, who was not involved in the Penn State research, found in another study that even people who lose weight on a diet high in fruits and vegetables said they wouldn't stick to the meal plan. "Many people said they were not going to spend the extra money on fresh fruits and vegetables, or shop more often, or spend more time preparing them," he said.
For the moment, Mattes added, Americans don't seem eager to embrace healthy diets. The very premise of the latest study, covert feeding to encourage better eating, underscores the resistance. "It's interesting that we have to go to such extents to get people to consume" more vegetables, he said.
The latest government diet guidelines recommend limiting portion sizes and filling half one's plate with fruits and vegetables rather than meat or carbohydrates.