The Weekly Newsmagazine of Science
Volume 155, Number 17 (April 24, 1999)
By J. Raloff
The body's natural sensors aren't very good at recognizing how many calories a person has just eaten. The fallibility of this satiety feedback system makes it easy to overindulge in calorie-rich foods, such as those high in fat. It may also allow the body to feel satisfied after eating less than its normal complement of calories, a pair of studies now finds.
The new research, reported this week at the Experimental Biology '99 meeting in Washington, D.C., hints at how cooks might discourage overeating by making each calorie more filling.
In the more provocative of their two new studies, Barbara J. Rolls and Elizabeth A. Bell of Pennsylvania State University in State College found that water can play different roles in satiety, depending on how it is consumed.
On three separate occasions, they fed a 270-calorie appetizer of chicken-rice casserole to 24 lean young women and then measured how much lunch each ate afterward. When the women started with the casserole alone or along with a 10-ounce glass of water, they went on to eat another 300 calories of food, on average. However, when 10 oz. of water was added to the casseroletransforming it into a soupeach woman consumed just another 200 calories.
Though the women ate about 27 percent fewer calories after the soup-based starter, "it didn't leave them feeling hungrier later in the day," Rolls notes. Each ate the same calories at dinner as she had in the other phases of the trial.
What makes this differential effect especially striking, Rolls points out, is that when the women drank the water, they were instructed to down it along with the casserole. "They took a sip, then a bite, then a drink, then a bite. We wanted it to enter the stomach and be dispersed with [the casserole's] nutrients the same way as with the soup."
These data reinforce the idea that food and drink affect hunger and satiety systems "through entirely different mechanisms. And when the water is in soup, it's no longer processed as a drink but as a food," Rolls told Science News.
In a second, 5-week-long study, Rolls and Bell recruited 34 women to eat all their meals in the researchers' laboratory for 4 days each week. In the first week, the women could dine on their choice of a wide range of foods. From then on, part of every mealequivalent to about half the calories that each woman had eaten per meal during the first weekwas compulsory. After finishing the mandatory foods, however, the women could eat all they wanted of other entrees and side dishes.
In this trial, the energy densitycalories per given weight of foodof the compulsory foods varied from week to week. During 2 weeks, the compulsory items were low in fat, but for one of those weeks they were energy-dense. Another week included high-fat, energy-dense compulsory items.
In general, the women responded to portion size rather than energy density of food. They ate the same size portions each day, regardless of whether the compulsory portion had been low in calories or high. As a result, they took in far fewer calories during weeks in which the mandatory food was low in energy density.
"The American population continues to get more overweight with every national survey," observes Susan B. Roberts of Tufts University who works at the Agriculture Department's Human Nutrition Research Center on Aging in Boston. Currently, she notes, more than half of U.S. adults are overweight.
Since so many low-fat foods are actually very high in calories, she says, "it's legitimate to begin switching our focus from dietary fat to caloric density." However, "to make these calculations you practically have to be a professional," she adds. She and Rolls both say food labels should begin listing caloric-density measurements.
From Science News, Vol. 155, No. 17, April 24, 1999, p. 261. Copyright © 1999, Science Service.
Copyright © 1999 Science Service