“Calorie density is the number of calories in a given portion or a given bite of food,” explains Barbara Rolls, director of the Laboratory for the Study of Human Ingestive Behavior at Penn State.

How does calorie density affect weight?

Rolls’s studies have found that people consume fewer calories when they’re offered foods with fewer calories per bite.

A 1999 study was one of the first.

“Before lunch, we gave people either a chicken-rice casserole, the same casserole with 1½ cups of water to drink, or a soup we made out of the casserole plus the water,” says Rolls. All three “preloads” had the same ingredients and the same 270 calories.

“The soup much more effectively reduced subsequent intake,” says Rolls.

The participants ate 290 calories at an all-you-can-eat lunch buffet on days they got the soup, but they downed roughly 400 calories on days they got the casserole, with or without the glass of water.

What about water intake?

Not all studies agree on drinking water. “In one study in older individuals, drinking two cups of water before meals helped with weight loss,” notes Rolls.

Still, she says, “it’s better to eat your water, not just drink it. When you drink water, it empties out of your stomach more quickly.”

It’s not just soup. The best way to add water to your diet: eat more fruits and vegetables.

In a 2007 study, Rolls randomly assigned women with obesity to either eat less fat or eat less fat and eat more fruits and vegetables for a year.

“The group that ate extra fruits and vegetables lowered their calorie density more, and they were eating a better-quality diet,” says Rolls.

After a year, the fruit-and-veggie eaters had lost more weight (17 pounds) than the other group (14 pounds), and they reported being less hungry.

Bottom line

“Bulking out your diet with fruits and vegetables is a win-win,” says Rolls.

Photos: Jennifer Urban/CSPI.