Volumetrics is the brain child of Dr. Barbara Rolls, a professor of clinical nutrition at the Pennsylvania State University and the University of Pennsylvania's school of medicine. Dr. Rolls is the author or co-author of over 250 papers published in the medical journals and six books. She is recognized as one of the world's best known scientific experts on the subject of obesity.
Dr. Rolls teaches people who want to lose weight how to take off the pounds without dieting. The fundamental principle of her now-famous volumetric diet is satiety. People (who don't have food addictions or other addiction issues) stop eating when they feel satisfied. The greater the satiety after a meal, the longer it will be before the person eats again. Increasing satiety helps people lose weight without dieting, and the principle way in which people achieve satiety with a meal is by feeling full. It is not possible to lose weight without reducing calories, but it is possible to reduce calories without feeling hungry.
The best way to avoid hunger is to "fill up" on low-calorie foods, and the lowest of all low-calorie ingredients is water. The more moisture there is in a food, the more it satisfies hunger. Drinking water doesn't result in food satisfaction, because it quenches thirst, not hunger. Water in food adds bulk to the food, filling up more of the stomach, causing the food to take longer to be digested, keeping the stomach fuller, longer. The more "moist" foods you eat, the less you want to eat.