There's a common notion that people tend to eat the same number of calories from day to day. But that's not necessarily so, says Barbara Rolls, PhD. Many people eat the same weight of food from day to day. Therein lies the strategy behind her new weight loss book, "Volumetrics." If people consume the same volume of food they always do but with fewer calories than usual, they'll lose weight, without feeling hungry.

Dr. Rolls has the credentials to weigh in. Unlike so many fad diet "experts" whose primary objective is to sell books, she is a nutrition and obesity researcher with years of scientific study to her credit.

The research, which was conducted at Penn State University, served women similar meals and snacks over several different days but varied how many calories the meals contained per pound.

On some days the women ate a pasta salad that had more vegetables than pasta. On other days, the salad contained more pasta than vegetables, which upped the amount of calories per bite. The women were allowed to eat all the food they wanted.

The women ended up satisfying their hunger by eating the same daily food weight-about 3 pounds. As a result, on some days they were satisfied with 30% fewer calories. The researchers explain that as the stomach fills and the food is broken down into tiny particles satiety occurs whether a pound of food contains five hundred calories or fifteen hundred.

The book rates more than 600 foods for their calories per gram of weight. Not surprisingly, vegetables and fruits rated very well on the calorie per pound scale. The book points out that it's sometimes easier to lower the energy density of a dish like lasagna by adding, say, spinach or eggplant rather than taking out fat by removing cheese.

But the best point, perhaps, is that "not every food choice you make should be determined by energy density" because some foods, "like chocolate, are too delicious to give up." Now that's our kind of weight loss book.