What is Calorie Density?

Q and A with Researcher Barbara Rolls

Barbara J. Rolls, PhD is one of the nation’s leading researchers on why people eat the way they do.

She is Director of the Laboratory for the Study of Human Ingestive Behavior at The Pennsylvania State University. Dr. Rolls’s studies on nutritional strategies for weight management have been published in leading scientific journals and she is author of the ground-breaking book Volumetrics.

AICR: What is calorie density?

Rolls: Calorie density is a property of food. It simply refers to the number of calories in a given amount of food.

AICR: What influences a food’s calorie density?

Rolls: The main influences on calorie density are the water content of food and the fat content. Water is the largest component of food and it has the biggest impact on calorie density. The more water a food has (fruits and vegetables, for example), the more it dilutes the calories and lowers the calorie density.

Fat, on the other hand, raises the calorie density. So getting fat out wherever you can – especially the animal fats, the saturated fats – is a good, healthy thing to do.

AICR: Why is thinking about a food’s calorie density useful?

Rolls: Research has shown that the amount (or weight) of food that people report eating on a daily basis is more consistent than their calorie intake. If people reduce the calorie density of their food choices enough, they can continue to eat the same amount of food, but take in fewer calories. For example, if you take the calorie density down by 30 percent, many people will eat 30 percent fewer calories without feeling hungry and without compensating for those calories at a later meal.

AICR: How do you lower the calorie density of a meal?

Rolls: By adding in more fruits and vegetables (water-rich foods) or taking a little bit of fat out.

AICR: Can you provide an example?

Rolls: Sure. Take an ordinary sandwich. Start with a small portion of lean meat, substitute the mayonnaise with mustard, bulk it up with your favorite veggies and add a whole-grain, high-fiber bread. On top of that, don’t drink the soda (have water instead) and eat some fruit. In the end, you can end up with some significant calorie savings – and you’re still eating the same amount of food.

AICR: How does this advice differ from the traditional “eat less” approach to weight loss?

Rolls: I think when you tell most people to “just eat less,” they don’t want to do that. They end up with a half empty plate and they say to themselves – before even eating it – “That’s not enough, I’m still going to be hungry.” But by choosing less calorie-dense foods (water rich foods and foods with a bit of fat reduction) you end up getting your usual amount of food, you get a healthier selection of food and you’re getting fewer calories.

AICR: In addition to increasing the proportion of fruits and vegetables in a meal and decreasing the fat, are there any other strategies you would recommend?

Rolls: Try having a big portion of a low-calorie salad, soup or fruit at the beginning of the meal. We think eating these low calorie density foods at the start of a meal is a good strategy. They help to fill you up and you have less room for the more calorie-dense foods that tend to come later in the meal.

AICR: Is there a take-home message here?

Rolls: Understanding the relationship between the calorie density of a food and how much of that food you can eat is important. Eating big portions of calorie dense foods is particularly problematic. I think people need to be aware of what is influencing the calorie density of their choices and try wherever they can to increase the water content – add fruits and vegetables – and to keep unnecessary fat down.


Q & A