A hundred calories of grapes fills about two cups. A hundred calories of raisins fits in a quarter cup. Same fruit, same calories, very different plate.
The difference is water, and it sits at the centre of an idea nutrition scientists call energy density: the calories packed into a given weight of food. Fat is the densest component, with nine calories in every gram. Water has zero. Swap some fat for water-rich ingredients such as vegetables, fruit or broth, and the energy density of a dish falls sharply. Fibre helps as well, since it adds weight and bulk without adding calories.
Why it matters at the table
People tend to eat a fairly steady weight of food each day. That is the catch with dense foods. Barbara J. Rolls, a nutritional sciences professor at Pennsylvania State University and author of the Volumetrics books, says light foods owe it to their water: eat them and the volume on the plate grows while calories stay level or drop. Fried onion rings and homemade chocolate chip cookies taste wonderful, but they do not trigger fullness until you have overeaten. Lean protein, soups, stews, cooked grains, nonfat milk, fruit and vegetables carry fewer calories per portion and satisfy more. Combine big portions with high density, as many fast-food meals do, and daily intake balloons.
The Centers for Disease Control and Prevention offers a handy ladder, as NutritionFacts.org describes it. Bacon sits at the top, packing plenty of calories into little space. A bagel lands in the middle. Fruits and vegetables are at the bottom. Two foods break the pattern: soda is so heavy that it looks milder than it is, while nuts carry so much fat that they look worse than they are.
What the studies found
In one trial, volunteers snacked on three apples, or three pears, daily on top of their usual diet and still lost a couple of pounds. A third group ate three cookies with enough oats to match the fibre, and did not lose weight. Researchers think fruit’s low energy density is what makes the difference.
A Hawaiian experiment went further. Participants were put on a traditional Hawaiian menu and allowed unlimited plant foods. Over 21 days they shed 17 pounds on average, and their cholesterol, triglycerides, blood sugar and blood pressure all got better. Calorie intake dropped 40%, yet they ate four pounds of food a day.
The research links modest cuts in energy density to modest weight loss, and bigger cuts to bigger loss. Anyone with a medical condition should consult a doctor before changing their diet. For shoppers, Rolls offers a quick test: set the calories per serving on the Nutrition Facts label against the serving weight in grams. A calorie figure below the gram weight marks a food as light.
Sources
- Eat More, Weigh Less (HealthyWomen)
- Eating More to Weigh Less with Energy Density (NutritionFacts.org)
