Posted on 02 Jun 2013 20:11
This explanation of nutrient density and empty calories takes the form of a video presentation. The article contains the exact transcript of the video.
Definition of Nutrient Density and Micronutrients
The nutrient density of foods is a factor related to the micronutrients in foods. Micronutrients are the small biological molecules in foods like vitamins, minerals or phytochemicals. Contrast this with macronutrients, which are the large nutritional units in foods such as proteins, carbohydrates, and fats. Calcium, Vitamin C, and beta carotene are micronutrients.
Nutrient density is defined as the amount of nutrients in a food as compared to its caloric content,
or more accurately, the amount of micronutrients per unit of energy. A food with a high nutrient density or a 'nutrient dense' food is one that has a high amount of micronutrients relative to its calorie count. An easy way to see this is to compare foods to their nonfat versions.
Measuring Nutrient Density
For instance, nonfat or skim milk has more calcium and vitamin A per calorie than whole milk.
Therefore nonfat milk is more nutrient dense. When dietitians or nutritionists tell us to choose nutrient dense foods, they are saying to choose foods with the most micronutrient bang for your calorie buck.
Empty Calories and Nutrient Density
Many sugary foods are called empty calories or junk food. This is because they have very low nutrient density. Sticking with calcium for our micronutrient of choice, let's ask whether cheddar cheese is more nutrient dense than nonfat milk.
To be precise we would compare the amount of calcium per 100 kilocalories or even 1000 kilocalories of each item. 100 Calories worth of cheddar cheese contains about 180 milligrams of calcium. Assuming it is not calcium fortified, 100 calories of nonfat milk contains about 366 milligrams of calcium. By this measure we see that nonfat milk is more nutrient dense than cheddar cheese for calcium.
Of course, we do not compare foods based on 100 calorie equivalents, we compare them based on a realistic serving. If we consider a serving of cheddar cheese to be 1.5 ounces, then that's around 170 calories and will yield around 300 milligrams of calcium. A serving of nonfat milk is usually considered 8 ounces, or one cup. That is around 83 calories, also giving 300 milligrams of calcium.
So, a serving of cheddar cheese contains more than twice the energy of the nonfat milk for the same amount of calcium.
Let's compare less similar foods for a different nutrient, thiamin. How about we compare a lean pork chop (say a center cut which has been broiled or grilled) with asparagus.
The pork is about 150 calories (remember, we've chosen a lean cut). That's about .5 milligrams of thiamin. One cup of steamed asparagus, on the other hand, is about 40 calories for around .3 milligrams of thiamin. You can see that the asparagus gives you more thiamin for your calorie buck.
In general, plant foods will always be more nutrient dense than animal foods, with certain notable exceptions such as iron and some other instances. Obviously, there is a problem with evaluating the nutrient density of foods by looking at one micronutrient. But when many common foods are compared, it is easy to see that the best way to achieve a nutrient dense diet is to eat more servings of a variety of plant based foods, including fruits, than meat or dairy products.
Of course, there is more to nutrition than micronutrients. For instance, you need essential fatty acids, like those from fish, nuts, and seeds. What understanding nutrient density allows you to do is meet your micronutrient needs before reaching your maximum caloric intake, allowing you what is called discretionary calories.
It is possible to loosely score general classes of foods in terms of overall nutrient density. Based on this, the most nutrient dense foods, in general, are raw leafy green vegetables. However, certain leafy green vegetables can be problematic, because of other chemicals like oxalic acid that can be harmful in excess. Romaine, kale, spinach, parsley, Swiss chard, and other greens are good choices.
A close second are non-leaf green vegetables such as those in the cabbage family, including broccoli and bok choy, and other veges like asparagus. Falling under this category in a culinary sense are foods which are actually fruits but used as vegetables.
Still, nutrient density is not the only way to rank foods and, as mentioned, there are harmful chemicals in food as well. It is not actually advisable to go on a leafy green 'fast' as is sometimes advocated. Even if you think fasting is a good thing, there could be other harmful effects due to certain phytochemicals which are fine in moderation but harmful when over-consumed.
There is yet to be any agreement on one ideal way to rate foods for nutrition. Nutrient density is but one factor and there is no need to become fanatical about it. It is about promoting adequate nutrition and general knowledge which helps you make healthy choices. You must combine the concept of nutrient density with variety.