Two Food Concepts Explained: Energy and Nutrient Density

by Charles Platkin, PhD

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, Ph.D., a nutrition researcher from Pennsylvania State University and author of The Volumetrics Eating Plan (Morrow Cookbooks, 2005). So, 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. This means that one Peanut Butter Cup (1.5 ounces, 230 calories) contains the same number of calories as — get ready — 60 ounces of celery.

How and why it works:
Generally, the energy density of a food is a function of its water content, says Adam Drewnowski, director of the Center for Public Health Nutrition at the University of Washington. Foods with a high water content, such as fruits and vegetables (which also tend to have a high fiber content), usually 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.

Dr. Rolls and her research team at Penn State have conducted numerous studies showing that people who eat a low-energy-dense diet consume more food by weight but fewer overall calories than people who follow a high-energy-dense diet. Plus, those eating the low-energy-dense diet included more foods that were low in fat and had higher intakes of several significant micronutrients, including vitamins A, C and B6, folate, iron, calcium and potassium.

Why it matters:
You’ve probably heard plenty about the importance of portion control in dieting — and for good reason. As a country, we have a dangerous tendency to overeat not only at home but especially when dining out. However, the bottom line is that no matter how careful you are about controlling your portions, you’re going to eat more if you still feel hungry. When you’re looking for foods that you can eat in large amounts without getting fat, the real key is finding those that are low in calorie density but will leave you satiated — that is, feeling full and satisfied instead of wanting more. Research has shown that it is indeed possible to consume fewer calories and still feel full. For example, studies conducted by Rolls have found that when people tended to eat food by weight, meaning the amount of food is most important, those who ate the low-density diet consumed 30 percent fewer calories daily than those on the high-density diet, although there were no differences in their ratings of hunger and fullness. The challenge, then, is to reduce the calorie density of the foods you choose while still maintaining the taste.

Why it’s not perfect:
According to P. K. Newby, Sc.D., M.P.H., M.S., a professor at Boston University School of Medicine and Boston Medical Center, “The tricky part is that 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 as people used to do 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.”

And although low-energy-dense diets are generally associated with high-quality foods, the problem is that just because a food is high in water content doesn’t necessarily mean it’s the most nutritious. “You can’t always neatly fit everything in nutrition into one simple concept: Nutrition is a science, and it is complex, as are all sciences,” says Newby. However, foods that are high in fiber and high in water tend to be low-energy-dense, whereas foods that are high in fat tend to be high-energy-dense, she adds.

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. Below are the categories — and some advice on how much to eat of the foods that fall into each one.

0.0 – 0.6 calories per gram — Great choices! Foods in this category really do defy the logic of portion control: They just don’t pack enough calories to make it an issue.

0.6 – 1.5 calories per gram — Good choices. Again, there’s no reason to worry yourself too much about portions when you’re consuming so few calories per bite.

1.5 &nash; 4.0 calories per gram — Keep your eye on how much you eat of these foods. While they’re fine in moderation, you shouldn’t overdo them.

4.0 – 9.0 calories per gram — This is a great time to look for a substitute or a Calorie Bargain — a food you can substitute that you find satisfying and that falls into one of the first two categories. That being said, we all have some special treats we don’t want to give up — but this is the time when portion control matters the most.

What is nutrient density?
Nutrient density is different from calorie or energy density. Nutrient-dense foods are those that contain a large number of nutrients (e.g., vitamins, minerals, antioxidants, etc.) and relatively few calories. In the scientific community, however, this would be considered a fairly crude definition. There is still much debate surrounding the exact formula for determining nutrient density. “When thinking about overall health and disease prevention, the concept of nutrient density in the diet is very important,” says Newby.

How it and why works:
Some nutrition experts say that a food should provide at least 1.5 times more nutrients than calories. Another way to say this is that it must provide 50 percent more in nutrients than it costs in calories.

For instance, a quarter-cup of sunflower seeds has about 200 calories, while a can of Sprite has only 140 calories. However the sunflower seeds provide 20 percent of the daily value for folate and vitamin B5 and more than 25 percent for phosphorous, tryptophan, copper, magnesium and manganese. Meanwhile, the 200 calories are only about 11 percent of daily calorie needs, so you’re getting twice as many nutrients as calories.

Drewnowski has developed a scoring system called the Naturally Nutrient Rich (NNR) score to help consumers identify nutrient-rich foods. The NNR identifies the nutrient-to-calorie ratio of foods. The initial version of the NNR Index was based on 14 nutrients: protein, calcium, iron, vitamin A, vitamin C, thiamine, riboflavin, vitamin B12, folate, vitamin D, vitamin E, monounsaturated fat, potassium and zinc. A more updated description of the NNR score added fiber and vitamin B5 (pantothenic acid), for a total of 16 nutrients. To get an NNR score for a serving of food, you add up its percentage of Daily Values (the amount of each nutrient 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 (16 in this case) — that’s its NNR score. The score ranges from 2 to 1,000. On the lower end there is soda, crackers and fried chicken, and the higher end has foods such as broccoli, liver and spinach. According to Drewnowski, anything over 100 has a good score; anything over 250 has an excellent score, and there are some scores in the stratosphere because of all the nutrients packed in with very few calories — specifically fruits and vegetables. For comparison purposes, 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 actually defined by good nutrients rather than absence of bad, whereas they had typically been defined by the absence of problematic nutrients (fat, sugar, salt) and not by the presence of beneficial nutrients they contain.

Why it matters:
Food is about more than just calories. There are many components, and nutrient-density ratings can help consumers make better overall food choices. The good news is that foods with a good fat content, such as avocados and nuts, also have high NNR scores. So do legumes, including peas and lentils, even though they have a relatively high energy density. For instance, “Chocolate does not have much calcium, so its NNR score will be low. On the other hand, cheeses score quite well, nuts score well, low-fat yogurts score very well, and avocados score well, too. So it is all about nutrients in proportion to calories,” says Drewnowski.

Why it’s not perfect:
While looking at the nutrient-to-calorie ratio is more informative then simply looking at calories alone, it’s not perfect. It doesn’t account for the bioavailability of these nutrients, the freshness or organic nature of the food, or the importance of antioxidants such as phytonutrients and carotenoids. It also doesn’t subtract points for added sugar, saturated fat or dietary cholesterol. Should there be separate scores for natural versus fortified foods or a higher score given for hard-to-get nutrients? These are just some of the concerns. 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. And whole-grain foods, which are low in water content, score low on the nutrient-density scale (and high in energy density), according to Drewnowski, even though they are considered healthy.

How to apply this to your life:
Well, it’s not easy to determine the NNR of the foods you eat. You would need to do the calculations, and as of now there are no online sources to look them up. However, if you look for colorful fruits and vegetables, whole grains, low-fat and non-fat dairy products, lean beef and pork, skinless chicken and turkey and legumes, you should be eating pretty well.

Bottom line: “Choose foods that are both low in energy density and high in nutrient density. That way, you are maximizing your nutrients and limiting your calories. Foods with a lot of added sugar and fat tend to be energy dense but not nutrient dense — especially when made with refined flour and hydrogenated (trans) fats. Those types of foods contribute a lot of calories but not a lot of healthful nutrients,” says Newby.

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