Eat more weigh less
The answer may lie in the new science of 'volumetrics'
The formula. Energy density is easy to calculate from a food label. Just divide the calories in one serving by its weight in grams, and you have the energy density of the food. To use Volumetrics for weight control, Rolls recommends making up a large portion of the diet with foods that have fewer calories in a serving than their weight in grams, resulting in energy densities below 1 (most fruits, vegetables, and low-fat dairy products). Also good are foods with calories equal to or slightly greater than their weight, or an energy density of 1 to 2 (beans, fish, chicken without fat or skin, potatoes, pasta, rice, low-fat salad dressings). Foods that have two or more times as many calories as their weight (ice cream, beef, french fries, cheese, pretzels, full-fat salad dressings, chips, cookies, bacon, oils) need to be controlled.
The Volumetrics principles are also useful for lowering the caloric density of whole meals. Rolls demonstrated the concept in her salad studies. Different groups of diners ate different sizes of salads with different energy densities. High-density salads had full-fat dressing and cheese, for example, while low-density salads were vegetables with fat-free dressing. She found that the diners who ate the large, low-density salads before a pasta entree ate about 100 fewer calories of pasta and 12 percent fewer calories for the meal. By contrast, the high-density salads increased the total calories by 17 percent. In a similar study of 200 overweight individuals on a weight-loss diet, those who ate soup as a snack twice a day lost 50 percent more weight than dieters snacking on dry, low-fat, calorie-dense foods, like pretzels or baked chips.
"We're being urged to manage calories," says Rolls. "So Volumetrics gives people a way to do that without having to count calories. If people understand where the calories are in foods, they can go for lower calories, lower density, and bigger portions of foods." Portion size and energy density independently contribute to the total calories of a meal, says Rolls, which is why restaurant eating is such a waist-expanding experience--energy density is high, and portions are large. "When people really get the energy-density message, they can accommodate in their diet some high-energy-dense foods in moderation," says Rolls. "But it's all trade-offs: You can eat a lot more apples than apple pie, but if you really want that piece of apple pie, it's better to accommodate it."
Food family. Rolls comes from a family fascinated by food. Her great-grandparents were farmers. Her grandfather, a professor at Cornell University, helped establish the New York agricultural extension program. Rolls grew up in Adelphi, Md., outside Washington, D.C., where her father spent most of his career at the U.S. Department of Agriculture. Her mother was a teacher and homemaker who struggled with food choices and weight control. "She was obese," Rolls says, "and she died of obesity-related illnesses--diabetes and cardiovascular disease."
A premed student at the University of Pennsylvania, Rolls graduated in biology and secured a fellowship to Cambridge University in England. She stayed in England, became a research fellow in experimental psychology and nutrition, and married Edmund Rolls, a professor of experimental psychology at Oxford. Her first studies of satiety were in the early 1980s. "My ex-husband was doing some neurophysiology experiments and found that cells in the brain stopped firing when we reached satiety with a certain kind of food but started firing again when we eat another food. This was fascinating because it meant that satiety is not global. It can be specific to the food or type of food you have been eating. People tire of salty or spicy foods and like the change to the sweet taste. So, when we have a variety of foods, we eat more."