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SHAPE UP |
Calorie (or energy) density and nutrient density are interesting concepts frequently discussed by health experts in the last few years. The focus of these discussions has been on how to get better, simpler information to people attempting to make good food choices. But what do these terms mean, and why are they important?
What is calorie density? Calorie (or energy) density refers to the number of calories per gram in a given food. The concept of looking at foods in terms of energy density was popularized by Barbara Rolls, a nutrition researcher at Pennsylvania State University. For example, just 1 gram of a Reese's Peanut Butter Cup has 5 calories, while 1 gram of celery has only one-fourth of a calorie. That means a 1.5-ounce peanut butter cup contains the same number of calories as 60 ounces of celery.
How and why it works: Generally, the energy density of a food is a function of its water content, said Adam Drewnowski, a researcher at the University of Washington. Foods with a high water content (which generally have a high fiber content) tend to have a low energy density and can fill you up without making you fat. The key is to feel full on fewer calories so that you don't consume more than your daily calorie budget.
Why it matters: Studies show we're satisfied as long as the portions we eat are the "right" volume — meaning the same size as what we would normally eat. Therefore, eating a diet rich in low-density foods allows you to eat a lot, but it won't cost you too many calories. Plus, those eating a low-energy-dense diet generally have higher intakes of several significant micronutrients.
Why it's not perfect: Said P. K. Newby, a professor at Boston University School of Medicine, "The concept of energy density doesn't really help consumers to distinguish between 'good' and 'bad' fats or, for that matter, 'good' and 'bad' carbohydrates. For example, nutrition scientists now know that you can't lump all fats into one group because they have different effects on health. Polyunsaturated fats, found in foods like nuts and fish, are quite healthful, as are monounsaturated fats, which are particularly high in olive oil. Saturated and trans-fats, on the other hand, increase 'bad' cholesterol and hence the risk of heart disease. All these fats have the same energy density but have very different effects on the body."
How to apply this to your life: There are four categories into which foods can fall. These are determined by calculating the number of calories per gram.
What is nutrient density? Nutrient-dense foods contain a large number of nutrients (e.g., vitamins, minerals, antioxidants, etc.) and relatively few calories.
How it works: Some nutrition experts say that a food should provide at least 1.5 times more nutrients than calories.
Drewnowski developed the Naturally Nutrient Rich scoring system to help consumers identify nutrient-rich foods. It identifies the nutrient-to-calorie ratio of foods and is based on 16 nutrients: protein, calcium, iron, vitamin A, vitamin C, thiamine, riboflavin, vitamin B12, folate, vitamin D, vitamin E, monounsaturated fat, potassium, zinc, fiber and vitamin B5. To get an NNR score for a serving of food, you add up its percentage of daily values (the nutrients contained in a single serving as compared with the recommended daily intake of that nutrient) and then divide it by the number of nutrients used. It ranges from 2 to 1,000. Drewnowski said anything over 100 is good; anything over 250 is excellent; and there are some scores in the stratosphere — specifically fruits and vegetables. Whereas jelly beans have a score of 3 and lard has a score of 35.
Why it works: By assigning values based on multiple nutrients, healthful foods are defined by beneficial nutrients rather than simply the absence of fat, sugar or salt.
Why it matters: Food is about more than just calories. There are many components, and nutrient-density ratings can help consumers make better food choices.
Why it's not perfect: It doesn't account for the bioavailability of the nutrients, the freshness or organic nature of the food or the importance of antioxidants. It also doesn't subtract points for added sugar, saturated fat or dietary cholesterol. Also, certain foods such as french fries score higher than they should on the nutrient-density scale. Potato chips score better than raisins or apple sauce.
How to apply this to your life: It's not easy to determine the nutrient density of the foods you eat — there is not one location of this information yet. However, if you look for fruits and vegetables, whole grains, low-fat and nonfat dairy products, lean beef and pork, skinless chicken and turkey and legumes, you'll be off to a great start.
Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.
