When Penn State researchers made small changes in young women's meals -- reducing calorie density by 30 percent and serving size by just 25 percent -- the women ate 800 calories less per day and felt just as full and satisfied.
Dr. Barbara Rolls, who holds the Guthrie Chair of Nutrition in Penn State's College of Health and Human Development, directed the study. She says, "We lowered the energy density, or calories per gram, of the participants' meals by incorporating more vegetables and fruit in recipes and also using food products reduced in fat and sugar. The subjects found the smaller, lower energy density meals just as palatable, filling and satisfying as the big, high calorie menu items -- and they didn't compensate for lowered intake on the first day by eating more on the second day of the study."
If you were eating a nominally sane (say, 2500 calories per day) diet and dropped 800 calories per day, you'd already be into calorie restriction territory. As practitioners have been saying for a while, it's quite possible to do this without feeling hungry if you are sensible about what you eat.