The term nutrient density means different things to different people. To epidemiologists, the term nutrient density of the diet means crude nutrient intakes (in g or mg) divided by the total energy intakes. In epidemiologic studies, nutrient density often means diet composition, as indexed by the percentage of energy from carbohydrate, protein, and fat. In developmental nutrition, a nutrient-dense food is one that delivers a complete nutritional package and can be used to sustain life. For example, Briend described a nutrient-dense infant feed as one composed of milk protein, peanut butter, oil, and sugar and fortified with vitamins and minerals. By contrast, in the cancer prevention literature, vegetables and fruit are classified as being
nutrient-dense, whereas the presence of oil and sugar would be enough to classify a food as being nutrient-poor. The literature mentions nutrient-dense carbohydrates,
nutrient-dense meats, nutrient-dense milk, nutrientdense fruit and vegetables, and nutrient-dense nuts.

As shown in the table below, the definition of nutrient-dense foods seems to encompass all grains, meats and dairy products, vegetables, and fruit.

Common examples of foods described as healthy, healthful, nutrient-dense, or nutrient-rich.

Term

What is meant

Nutrient-dense foods Milk, vegetables, protein foods, fruit, grains
Nutrient-dense food groups Dairy, fruit, grain, meat, vegetable groups (LND foods excluded)
High-nutrient-density foods Fruit, vegetables, milk, whole-grain products
Nutrient-dense beverages 100% juice, milk
Nutrient-dense foods Fruit, cheese, yogurt, cereals
“Good” foods Fruit, vegetables, cucumbers, spinach, tomatoes, beans, low-fat milk, whole-grain bread, oats, salmon, fish
Healthy foods Fresh fruit, cooked vegetables, raw vegetables and salad, olive oil
Healthy foods Fish, fruit, vegetables, nuts, whole-grain cereals
Healthful foods Fruit and vegetables, meats, grains, dairy products
Healthy foods (diabetes) Diet soda, 1% or skim milk, high-fiber bread, low-carbohydrate bread, fresh fruit,
fresh tomatoes, fresh green vegetables
Healthful snacks Vegetables, fruit, pretzels, yogurt
Healthful vended snacks Pretzels, peanut butter and cheese crackers, peanuts, almonds

In the absence of agreed-on standards, there are continuing differences of opinion as to which foods are truly nutrient-rich. For example, in 1979, Hansen wrote that “with the exception of thiamin, the nutrients provided by breads and cereals are not particularly notable”. In his view, the main importance of cereals was that they provided calories, protein, thiamine, calcium, and iron at a very low cost. In contrast, other researchers have described breads and cereals as being nutrientrich, and the current literature refers to nutrient-dense carbohydrates and nutrient-packed whole grains.
There are also differences of opinion regarding fruit juices: some researchers describe 100% juices as nutritious, whereas others do not. In an extreme case, even the nutritional value of milk was challenged, as described in a recent review.

There have been several attempts to formally define what is meant by nutritious foods. In 1974, the FTC proposed to limit the use of the term nutritious to foods that provide more than 10% of the US RDA for protein and 3 other nutrients per 100 kcal and more than 10% of the RDA per serving for one of these nutrients. However, as Guthrie had pointed out, only one vegetable and one milk out of a total of 135 different foods met those very stringent criteria. Burroughs then suggested that the foods designated as nutritious ought to provide 50% of the US RDA for one nutrient, 20% for 2 nutrients, 15% for 3 nutrients, 10% for 4 nutrients, and 6% for 5 nutrients. The last criterion was apparently based on the assumption that each person consumes 15 different foods per day, so if each of those foods were to provide 6% of nutrient requirements, the person would be well-nourished. However, Burroughs’ criteria were almost as strict. Such foods as tomatoes, whole-wheat bread, Cheddar cheese, and peanut butter
failed to qualify under that standard. Similarly, in a more recent study of vending sites at a large university, only 4 of 133 unrefrigerated snacks met a nutrients-for-calorie criterion for nutrient density that was based on 7 nutrients and fiber.
Aiming to quantify nutritional value, Hansen et al suggested that such terms as poor, fair, adequate, good, or excellent might be used to reflect the gradations of nutrient density. That was an early precursor of the FDA criteria for the allowable use of such terms as “a good source of” and “excellent source of.” Those terms are based on percentage DVs, but they apply to only one nutrient at a time and not to the total nutrient package. Health claims are permitted if the food, before fortification, contains
more than 10% per serving ofDVfor protein, calcium, iron, vitamin A, or vitamin C. The FDA definition precludes health claims for fruit and vegetable products with added oils, salt, sauces, or syrups as well as some breakfast cereals. In keeping with the FDA position, the National Cancer Institute excluded from its definition of healthy foods processed fruit and vegetables that contain sugar or fat or that contain more than 480 mg Na. However, that position may be changing. In 1995, the FDA invited comment on whether processed vegetables and fruit ought to be exempted from the minimum nutrient requirement. The FTC response was that frozen vegetables in sauce or canned fruit in light syrup can contribute to healthier diets and that a nutrient density standard
would allow health claims for many of those relatively nutrient-rich foods.

Some concepts of nutritional value depend on membership in a given food group. For example, the National Cancer Institute included in its former definition of healthy foods all fruits and vegetables in their natural form, with the exception of avocados, nuts, olives, and coconut. The exclusion of avocados, now rescinded, was based purely on fat content and did not take the beneficial nutrients in avocados into account. Recognizing that not all foods within a food group have the same nutritional value, the World Health Organization defined nutrient-dense foods as whole grains, lean meats, low-fat dairy products, and all legumes, vegetables, and fruit. Going beyond the sugar and fat contents of foods, the Food Guide Pyramid emphasizes that dark green leafy vegetables and legumes are especially good sources of vitamins and minerals and recommended fresh fruit, fruit juices, and frozen, canned, or dried fruit. There was no prohibition
against nuts, which wee included alongside meat, poultry, and fish.

In contrast with the systematic approach adopted by the health agencies, many other attempts to grade the nutrient density of individual foods appear arbitrary, tautologic, and imprecise. In the Traffic Light Diet, individual foods are categorized as green, yellow, or red on the basis of their (unspecified) nutrient density. Red foods are described as being higher in energy density than the foods in the other groups. Green foods (most vegetables and fruit) are described as “very high” in nutrients and low in fat. In another study, foods of moderate nutrient density were simply described as being less nutrient-dense than were the foods that were high in nutrient density. In the examples
given, fat-trimmed beef was contrasted with skinless poultry, low-fat with nonfat milk, and candied sweet potatoes (one of the highest sources of carotenoids found in nature) with plain vegetables.
For reasons that were not clear, the former were all deemed to be less nutrient-dense than the latter. Working with a list of 60 Swedish foods, Michels and Wolk stated that they “simply” categorized foods as good or bad on the basis of their (unspecified) nutrient content and on data from large epidemiologic studies. All meat was bad and therefore not recommended; white bread (high glycemic index), cheese (too much saturated fat), and margarine (trans fatty acids) were also not recommended. Poultry did not make the list of recommended foods because the researchers did not consider chicken to be a health-promoting food; juices (too much sugar) and boiled potatoes (high glycemic index) also did not make the list. Whole milk and 3%-fat yogurt were judged to be about as desirable as alcohol and did not count toward either food score. Escaping censure were crispy rye bread, lettuce, cucumber, tomatoes, salmon, herring, and other fish (except shellfish)—in other words, the classic ingredients of an open-face Swedish sandwich.
When it comes to deciding which foods have nutritional value, some researchers seem to share the viewpoint of the Supreme Court Justice Potter Stewart: “I know it when I see it”.

This article was extracted from “Concept of a nutritious food: toward a nutrient density score”, by Adam Drewnowski, published on the American Journal of Clinical Nutrition.

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