When assessing whether a particular food is beneficial for you or not, energy density vs nutrient density is an important consideration to make. In general, you should seek out nutrient density for health.
Density is a physical property of matter that describes the relationship between mass and volume (density = mass / volume). However, when talking about energy density, we refer to energy (kilocalories or kilojoules) / volume. Therefore, energy dense foods are those that pack a lot of energy in a small volume.
Energy dense foods are often high in fat (because fat is the macronutrient with the most energy per gram: 9 kilocalories or 37 kilojoules) and/or sugar. In addition, many are highly processed and may have high amounts of sodium. Sounds familiar? Yes, this pretty much describes discretionary choices (a.k.a. junk food). However, energy dense foods are not inherently unhealthy. Other considerations include the portion size that is actually consumed (which can be larger than the serving size indicated in the label) and the food’s nutrient density. For example, extra virgin olive oil, nuts and seeds are energy dense, but they are rich in nutrients and not usually consumed in large quantities.
As explained in my article How to read food labels, it is usually easier to compare similar products per 100 grams (for solids) or 100 millilitres (for liquids). Grams is a measure of mass, so, strictly speaking, energy per 100 grams does not equal energy density. However, it is a good indicator of energy density and is readily available in nutrition information panels.
Nutrient density is the amount of nutrients contained in a food per unit of volume. We normally focus on nutrients that play important roles in the body, such as vitamins, some minerals, fibre, essential amino acids and essential fatty acids.
Because there are many important nutrients and their contents are not always easy to know or find, assessing nutrient density is quite a chore. However, it is safe to assume that most unprocessed vegetables, fruit, nuts, seeds, fish, eggs, meat and poultry are all nutrient dense.
Energy density vs nutrient density
Energy density and nutrient density exist in spectrums within the same food. This means that some can have high energy and nutrient density, high energy density and low nutrient density, low energy density and high nutrient density or low energy and nutrient density. And everything in between. See the image below for a graphical depiction of this.
What you can notice in the graph is that, as a general rule, energy-dense nutrient-poor foods are not ideal and energy-poor nutrient-dense are the best. Energy-dense nutrient-dense are also good, but you might not want to eat lots of them if weight management is important for you. Finally, energy-poor nutrient-poor foods are “meh”. Below are some examples of foods that fall into each category:
- energy-dense nutrient-poor: confectionery, processed snacks, cakes, ice cream, pastries, etc.
- energy-poor nutrient-dense: fruits and vegetables
- energy-dense nutrient-dense: nuts, seeds, meat, poultry, fish, eggs
- energy-poor nutrient-poor: iceberg lettuce and similar vegetables that are mostly water
Summary and recommendations
Energy density and nutrient density are good indicators of whether a food is healthy or not. In general, the bulk of the diet should be nutrient dense. If you need to control your weight, most of those foods should be lower in energy. Foods low in energy and nutrients are optional fillers.