Eat well! Lose weight! What sounds like a common diet gimmick is the science behind Penn State nutrition professor Barbara Rolls' new book, The Volumetrics Eating Plan.

The new book, which is part cookbook, part lifestyle guide, is a sequel to Rolls' 2000 book, The Volumetrics Weight Control Plan. Eating Plan was released March 1.

"Right now, who isn't concerned with their diet?" Rolls said.

"Volumetrics is based on a term from physics that means 'measurement by volume,' " she said, "and you can't really talk about 'weightametrics.' "

Volumetrics relies on measuring food by weight and analyzing the number of calories per bite in order to determine a food's energy density, said Jenny Ledikwe, a postdoctoral fellow in the Laboratory for the Study of Human Ingestive Behavior.

"People generally eat a consistent weight of food, but not the same number of calories," Ledikwe said. Volumetrics is the practice of making that same amount of food contain fewer calories.

"Volumetrics is about satisfying portions," Rolls said.

Fats, oils and sweets have a very high energy density, whereas foods that contain mostly water, like most vegetables and fruits, have a low energy density, Ledikwe said.

Consequently, these water-based, low energy density foods are preferred for the diet. Foods with the lowest calories per bite are ideal.

The nutritionists behind The Volumetrics Eating Plan wrote 125 volumetric recipes. "Most of the recipes are easy, and many were intended to be fast," Ledikwe said.

She said many of the recipes they developed were based on popular dishes. For example, to make pizza volumetric, the nutritionists created a recipe for Chicken Fajita Pizza.

"By loading a pizza with veggies and chicken, you can reduce its energy density," Ledikwe said. "You can feel fuller on a smaller amount of this pizza."

Jennifer Meengs, lab manager and registered dietitian, said she contributed her fruit-smothered whole-wheat buttermilk pancakes, based on a recipe she makes every Sunday morning for her family. She said her 3-year-old son approves of the volumetrics version.

Other recipes include creamy broccoli soup, shrimp creole and Santa Fe steak salad with lime cilantro dressing. There is even a recipe for quinoa, a South American grain recipe, developed by Rolls' partner, Charlie Brueggebors.

"We tried to come up with some really healthy dishes," Ledikwe said. "We really tried to have a variety."

Rolls does acknowledge criticism of volumetrics. In a time when diets revolve around eliminating one particular macronutrient, like carbohydrates or fat, Volumetrics is "a shift in thinking, a different approach, considering all the macronutrients," Rolls said.

Volumetrics will also require long-term clinical trials for weight loss, she said.

"However, it's such a nutritious approach to weight loss -- even if people do not lose weight they'd still be eating a better diet," Rolls said.

Rolls has been promoting the book through a number of different outlets, appearing on NBC's Today show and the CBS Evening News. Articles about volumetrics have appeared in a wide range of magazines, such as Eating Well, Fitness, Glamour and U.S. News and World Report.

The New York Post also featured a story, unbeknownst to Rolls, entitled "Stuff It: Pig out and get skinny."

"I'm not sure I'd have approved that one," Rolls said.

But most magazines, Rolls said, are looking for reliable nutritional advice.

"It is sound, practical advice that can be utilized for weight loss. It's not that much more difficult than counting calories," Meengs said.

As of Sunday, The Volumetrics Eating Plan was ranked No. 223 on Amazon.com's best-selling books.