Eat more weigh less
The answer may lie in the new science of 'volumetrics'
Spice of life. In a series of experiments, Rolls looked at how variety influences the amount of food people eat. Students fed four courses at a meal ate 60 percent more than when they were served just one of the foods. When student nurses were offered sandwiches for lunch with either one filling or four different fillings, they ate 33 percent more food when offered the variety. Even the shape of food affects how much people eat: Volunteers ate 15 percent more pasta when served three different shapes than when served only one. "This is why it's important to have on hand a variety of low-energy-dense foods [oranges, pears, apples, carrots, celery, salad greens, soup, stew]. Otherwise, we eat high-density foods that are all too readily available [chips, crackers, cookies, pizza, fast-food burgers, and fries] because we want variety."
Rolls divorced and came back to the United States in 1984 with her two daughters, Juliet and Melissa, to an associate professorship in psychiatry at Johns Hopkins School of Medicine. "Members of the department were interested in the role gut hormones play in satiety," she says. She became a full professor in 1991 and made the move to Pennsylvania State in 1992 when the university offered her the directorship of the school's new Laboratory for the Study of Human Ingestive Behavior.
"I spent the 1990s comparing proportions of carbohydrate and fat because that's where the action was," she says, meaning the research money. "But we really weren't finding much difference in the effect of fat or carbohydrates on the total calories people ate. So, I noticed that people were eating the same weight or volume of food. I remember going to meetings where everybody was talking about the right proportion of fat or protein in the diet, and I'd say, 'Look at the weight of the food people are eating! It's the same, whether it's high in fat or carbohydrates.' See, we all thought people were eating for calories, the same number of calories per day. But they weren't. They were eating for the same weight or volume of food." The idea of Volumetrics was born.
Much nutritional research still focuses on macronutrients, or the ratio of fat, protein, and carbohydrate in the diet. Clinical studies on the effectiveness of low-carbohydrate versus low-fat diets for weight loss are still underway, but so far most show similar outcomes and modest long-term results. In fact, much of the public remains confused about these seemingly contradictory diet strategies, in part, as Rolls puts it, "because there has really been a lot of controversy in the field over fat. Understanding energy density resolves a lot of these issues." Both high-fat foods and foods high in refined carbohydrates are energy dense and make weight control difficult.
One of the first studies on this subject was done not by Rolls but by researchers at the University of Alabama in 1983, who found that people on a low-energy-dense diet reached satiety with about half the calories of those on a high-density diet. Rolls uses the study in her presentations and laments that the researchers didn't continue it. But that article and Rolls's subsequent studies began to influence those working in the weight-loss trenches. "I was in private practice at that time," says James J. Kenney, nutritionist at the Pritikin Longevity Center. "I had this one woman who wasn't losing weight on a low-fat diet. I started looking at what she was eating, and everything was dry: dried fruit, dried cereal, dry crackers, energy-dense foods." When she switched to soups, salads, fresh fruit, and vegetables, her weight dropped.