Eat more weigh less
The answer may lie in the new science of 'volumetrics'
Three young women scurry back and forth from the stainless steel counters to the big walk-in refrigerator, loading plates, written instructions, and questionnaires on trays in this commercial-style kitchen. But this is not like any other restaurant kitchen. The staff members not only prepare the food; they carefully weigh, measure, and record the food before it's served. They also weigh and measure what diners leave on their plates.
The adjoining dining room is also not typical. There are 16 individual cubicles separated by short walls and long, blue curtains, rather like the instant-photo booths once found in variety stores. Buffet tables are set up where dishes are kept hot. Small, unobtrusive video cameras record food selections at the buffet and the eating habits of diners inside the booths, all of it broadcast to monitors in the kitchen and in some of the offices surrounding the dining room.
Welcome to Pennsylvania State University's Laboratory for the Study of Human Ingestive Behavior, one of the world's most sophisticated centers for the study of what and how humans eat. The queen of this quirky culinary empire is Barbara Rolls, professor and Guthrie chair in nutrition at the university. For nearly three decades, Rolls, 60, has researched food choices, portion sizes, the caloric or energy density of foods, and myriad other factors that influence the human appetite and what satisfies it.
Most recently, the lab has been studying the impact of energy or calorie density--that is, the number of calories in a given weight of food--on satiety and weight control. Rolls calls this research "Volumetrics," and her new book, The Volumetrics Eating Plan, arrives in bookstores this week. Part weight-control program, part cookbook, it is an effort to put into practical form a lifetime of study on why people eat what they do and how to satisfy the human biological drive for abundant food while achieving a healthy weight.
It was Rolls who realized that satiety, or the sensation of fullness, is "food specific." That is, when people are full of one food, they can still eat another--an explanation, says Rolls, "for why you always have room for dessert." She was among the first to notice that humans eat about the same weight or volume of food every day but not the same calories, a notion now accepted by nutrition scientists.
Supersize. Yet she also discovered an apparent contradiction: When food portions are "supersized," people eat more. Adults offered four different portions of macaroni and cheese at her lab ate 30 percent more calories when given the largest portion, compared with the smallest. Fewer than half noticed any difference in the serving sizes. Likewise, in Rolls's sandwich experiments, men and women were served 6-, 8-, 10-, and 12-inch submarine sandwiches. When given the 12-inch sub, women ate 31 percent more calories and men 56 percent more--compared with those given the 6-inch sub. Asked to rate their fullness after lunch, diners reported little difference whether they had eaten the larger or smaller sub. In a two-day study, portion sizes were increased for some dishes by as much as 100 percent, and people continued to eat more over both days. "As to why people respond this way, I don't know, but that is part of what we're working on," Rolls says. "Clearly, visual and cognitive cues are important."
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.
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."
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.
Once at Pritikin, Kenney suggested the center change its emphasis from the low-fat regimen that the program had been founded upon to one emphasizing a lower-caloric-density approach. Kenney was fearful that the wave of low-fat but high-energy-dense cookies, crackers, and snack foods hitting the market would lead to more obesity and confuse the public about the usefulness of reducing fat calories. "And that's just what happened," he says. "In the 1990s, we saw Americans gaining weight like never before . . . . The public has been oblivious to the very important role calorie density plays in how full people feel when they eat a set amount of calories."
Of course, a small group of elite dieters who attend some of the premier weight-control centers have been schooled in energy density. At the Duke Diet and Fitness Center, as at Pritikin, nutrition manager Elisabetta Politi has been using an energy-density approach for a few years. "I think Barbara Rolls has a great theory, and there is a lot of interest in it," says Politi. "We take advantage of what she's found in what we do here. We start with a big salad, soup, smaller servings of protein and higher-density foods; and our clients feel satisfied on 1,200 or 1,300 calories a day." Likewise, Brian Zehetner, the lead nutritionist at Canyon Ranch SpaClub at the Venetian in Las Vegas, says, "We promote foods that are high in fiber and water. They add bulk, but it's not calorie-containing bulk. So theoretically, you can decrease your calorie intake and eat more food while eating low-energy-dense foods compared to eating high-energy-dense foods." Rolls wants Volumetrics to be accepted by a wider audience, however. She's now on the board of the Jenny Craig weight-loss program, and she notes that Weight Watchers seems to be incorporating aspects of Volumetrics as well, though she quibbles with both of these programs.
Paradigm. If the majority of the public, outside of a few weight-control programs, has been oblivious to the role energy density could play in cleaning up the American diet, so have many nutritional scientists. "This is a paradigm shift," agrees Gary Foster, clinical director of the Weight and Eating Disorders Program at the University of Pennsylvania School of Medicine. Volumetrics is "an overarching concept, less based on macronutrients, though clearly, high-fat foods have higher energy density. It's a more unifying approach to diet, and there are data to support it." The downside, Foster says, is that energy density is not listed on food labels. Rolls hopes that will change: "If we had an energy-density number on food labels, it would give people an immediate way to compare foods and the calories in a portion."
"My sense is people are becoming disenchanted with a low-carbohydrate diet, which is a high-energy-dense diet," says Columbia University's Xavier Pi-Sunyer, a member of the dietary guidelines advisory committee and director of the Obesity Research Center at St. Luke's-Roosevelt Hospital Center. "So this would be a return to a lower-energy-density diet. And that is in line with the new guidelines."
The grocery bill for a week of Volumetrics meals may be higher, says Adam Drewnowski, director of the Nutritional Sciences Program at the University of Washington. "On a per-calorie basis, fruits, vegetables, fish, lean protein, and low-fat dairy products are more expensive sources of pure calories. But we spend so little on food and so much on our cellphones; it really should be the other way around." Drewnowski is an advocate of a diet based on its nutrient density. "But Barbara and I end up in the same place--eating more fruits, vegetables, whole grains, water, and fiber-rich foods, which are nutrient dense."
Foster, Drewnowski, and Pi-Sunyer, like Rolls herself, would like to see Volumetrics and the energy-density concept fully evaluated in long-term clinical trials. "Let's roll this out now to three or four different centers," says Foster, "and see how it works for 300 to 400 people."
A longtime practitioner of Volumetrics, Rolls herself is slim. She swims every day in a lap pool at her house on a mountaintop near the university, walks on campus, takes the stairs instead of the elevator, and encourages people to use step counters to monitor their activity. A past president of the North American Association for the Study of Obesity, Rolls is no ascetic, however. She loves good food, and as she puts it, "I save my juice calories for wine." She and her partner of seven years, Charles Brueggbors, an architect turned foodie, developed the recipes in the book. Brueggbors came to a Volumetrics diet before he met Rolls, after consulting a dietitian some 15 years ago when he developed hypertension and a spare tire. "I still want chips; I still want sausage," Brueggbors says. "But I've learned to like the fresh veggies and low-fat foods, too. And so now I have chips, but I get a bowl, put in a small amount, and when it's gone, I just don't go back."
It's lunchtime, and the first volunteer diner enters the laboratory and is seated in a curtained booth. He's told he may take his plate to the buffet, get as much as he wants, and go back as often as he wants for any of the four dishes: a chicken and noodle casserole; a creamy, green bean and fried onion dish; a broccoli salad; and whipped sweet potatoes. Most diet programs recommend using a small plate to reduce calories in a meal. "We're not finding it's true," says Rolls. "People just go back for more."
Rolls watches on a video monitor as the man makes his way to the buffet table for the third time, piling the noodle casserole and the green bean and onion rings concoction onto his small plate. "Look at that," Rolls laments. "He's not even touching the broccoli salad."
Clearly, we have a long way to go.
This story appears in the March 7, 2005 print edition of U.S. News & World Report.