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."

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