Eat more weigh less
The answer may lie in the new science of 'volumetrics'
What has become clear from her Volumetrics studies is that the key to weight management lies in "food choices that help you feel full with fewer calories." The absence of satiety is one reason most "diets" don't work very well or for very long. "Satiety is the missing ingredient in weight management," Rolls writes, and she's impatient with those who say the nation's obesity epidemic can be reversed by "telling people to eat less. People need to eat more low-energy-dense food, such as fruits and vegetables, so they get a satisfying amount of food and enough calories." This view is echoed in the 2005 Dietary Guidelines for Americans. And studies show that encouraging overweight families, for example, to eat more fruits and vegetables results in greater weight loss than telling them not to eat foods high in fat and sugar. "Emphasizing what people can eat rather than what they should not eat seems more sustainable," says Rolls.
In her lab, she tested these theories recently in the first yearlong clinical trial of Volumetrics, involving 97 obese women. One group was given Volumetrics ideas and encouraged to eat more fruits, vegetables, soups, whole grains, and legumes. The other group received more traditional and negative messages about restricting fat and portion sizes. Neither group counted calories or fat grams, yet both groups showed a similar reduction in fat intake, and both groups lost weight. "The low-energy-density diet group ate a greater weight of food over a year but lost more body weight--about 20 pounds," says Rolls. The group given negative messages, to eat less fat and smaller portions, lost about 15 pounds. While the 33 percent greater amount of weight lost by the Volumetrics group may not have made anybody skinny, the group also ate more fruits and vegetables--five servings a day compared with 3.5--and a diet lower in energy density and richer in important nutrients.
While the trial is encouraging, Rolls is the first to say that it's small. Volumetrics needs to be tested at a number of medical centers, among more participants, and over a longer time. "There is so much research money going into diets that change the proportion of macronutrients [fat, protein, and carbohydrates]," says Rolls. "Yet what we're advocating will lead people to follow the new dietary guidelines and optimize not only weight but nutritional status as well."
In many ways, the theory represents the ultimate "value meal": Eat more for less. The secret ingredients that make foods less energy dense are water and fiber, which explains why most vegetables are among the lowest-energy-dense foods available, while vegetable oils, with all the water and fiber removed, are the highest. The principle becomes obvious when thinking of fruit: One hundred calories of grapes represents a great deal more food in terms of weight and volume, and is more filling, than 100 calories of raisins, or dried grapes. The same is true for nearly any dish. The drier the food, the higher its energy density. Potato chips (dry and cooked in vegetable oil) are five times as energy dense as a baked potato. Pasta, which absorbs water as it cooks, is about half as energy dense as Italian bread, even though the ingredients are similar. Adding water or water-rich foods, like vegetables, and using oils and energy-dense ingredients sparingly lower the density of most dishes, allowing larger portions and increasing satiety.