"Energy Density" -- Not Fat -- Is Key To Feeling Full While Managing Weight

Dr. Barbara Rolls, who holds the Guthrie Chair in Nutrition, directed the study. She says, "You need to eat a satisfying amount of food to control hunger. Fat can make food taste good but it doesn't necessarily make you feel satiated."

The study is detailed in the May issue of the American Journal of Clinical Nutrition in a paper, "Energy density but not fat content of foods affected energy intake in lean and obese women." The authors are Rolls, Elizabeth A. Bell, doctoral candidate in nutrition; Victoria H. Castellanos, former postdoctoral student; Mosuk Chow, assistant professor of biostatistics; Christine L. Pelkman, doctoral candidate in biobehavioral health; and Michelle L. Thorwart, research technologist.

"When we first started this study, we thought that fat played an important role in satiety. We found that, when you keep the calories and volume of food that a person eats fairly constant, you don't see any special effects for fat in terms of reducing hunger."

Rolls, a faculty member in The College of Health and Human Development, added, "This experimental design closely resembles real-life situations in which a person who is concerned about his or her food intake may select some foods that are reduced in fat or calories but may also consume high-fat or high-calorie foods."

The women who participated in the study ate breakfast, lunch and dinner in Penn State's nutrition laboratories four days a week for five weeks. The study included both lean and obese individuals between 18 and 45 years of age. While the obese individuals ate more overall than the lean ones, each of the women tended to eat the same amount of food every day even though they could have as much as they wanted of everything that was served.

During two weeks of the five-week study, the women ate anything they wanted from the foods served so that the researchers could determine their usual caloric and food volume intake. However, during three of the study weeks, at each meal, each woman was served one compulsory entrée that contained about half her usual calorie intake. The calories, fat and energy density of the compulsory entrees were controlled so that the numbers of calories remained the same, but one week the entrée was low-fat, low-energy density; another week it was low-fat, high-energy density; and a third week high-fat, high-energy density.

For example, if the entrée was pita pizza, to make a low-fat, low energy density version, the nutritionists added more tomatoes. In fact, the low-fat, low-energy density versions of the dishes contained on average nearly a third more food, in the form of fruits, vegetables, water or fiber, than the low-fat, high-energy density dishes even though both versions contained the same number of calories.

After finishing the compulsory dish, the women could also eat as much as they wanted of a variety of side dishes to finish the meal. However, when the women ate the larger low-fat, low-energy density versions of the entrees, they ate less of the side dishes and snacks. In fact, they consumed 16 percent fewer calories during that study week. Nevertheless, they reported feeling as full and satisfied as when they consumed high-energy dense foods and more total calories. Whether the compulsory entrees were 16 percent fat or 36 percent fat didn't affect the participants' level of hunger or how much they ate. The only change that affected the women's eating habits was the variation in energy density.

Rolls says that following your usual eating habits but modifying some favorite recipes to reduce the energy density would be a sensible way of applying these research findings in a home kitchen. For example, you could reduce energy density by adding more water to turn a casserole into soup, or add leaner meat, celery, extra tomatoes and mushrooms to chili to increase bulk but not calorie content.

"People on diets often substitute pretzels for high-fat, high-calorie snacks. But pretzels have a low-water content and don't fill you up, so you eat more of them. A snack with higher water and fiber content, for example, an apple, would be a better choice," Rolls says.

The research shows you don't need high fat food to feel full. In fact, your body's natural satiety sensors probably won't even notice if you reduce the amount of calories and fat in meals by adding more water and fiber - and eat larger portions.

The research program was supported by grants from the National Institutes of Health and the International Life Sciences Institute Foundation.