Classes of Nutrients

Humans require six major classes of nutrients: water, carbohydrates, lipids, proteins, vitamins and minerals.

Nutrients are compounds that must be acquired from external sources to secure the amounts needed to sustain life. Extensive research led to the creation of target requirements for nutrients and recommended upper limits for most of them. We refer to these recommendations as the Dietary Recommended Intakes or DRIs.

There are six major classes of nutrients into macronutrients (water, carbohydrates, lipids & proteins) and micronutrients (vitamins & minerals).

Macronutrients and Energy

The macronutrients include water, carbohydrates, proteins and lipids. Of these four, all provide energy (in the form of kilocalories) except water. In nutrition, the proper label is kilocalorie (kcal) but popularly, you will see calorie used in its place. Because these four nutrients are required in relatively large amounts daily, they are all considered "MACRO"nutrients.

The amount of energy in each macronutrient depends on its biochemistry. For this general overview, it is useful to know that water contains zero energy, carbohydrates and proteins both contain 4 kilocalories (kcal) in every gram of carbohydrate or protein, and lipids (fats) contains the most energy per gram, more than double that for carbs and protein at 9 kcal per gram fat.

(Alcohol, while not a nutrient, certainly is a source of energy and is listed here-Alcohol energy content: 7 kcal/gram.)

* Note- fiber is a form of carbohydrate that contains energy that has a lot of value to the body; however, not all fiber is absorbed and utilized by the body's cells so, technically, fiber doesn't contribute much if any kcals.

It follows, then, that foods are combinations of carbohydrates, proteins and lipids. The amounts of each macronutrient in a food add up to the total calories in that food. As you might imagine, measuring the calories in foods is pretty straightforward.

On the other hand, the amount of energy (kilocalories) that a person requires each day depends on many factors, including gender, age, weight, height and level of activity. For older adults, energy needs generally decrease with age but it is important to always keep in mind that 'one size does not fit all'. Counting calories has never been a comprehensive solution to good nutrition and emerging science confirms that knowing more about dietary patterns as well as the macronutrients is critical to understanding energy balance and chronic disease risks more than a focus on specific vitamins and minerals.

Micronutrients

Included in the micronutrients are vitamins and minerals. A deficiency in a micronutrient can be as critical as a macronutrient deficiency. Some sources include some phytochemicals (biologically active plant-based components) and zoochemicals (biologically active animal-based components) in this category, however, vitamins and minerals are the only components at present that have specific daily recommendations based on a body of research.

Created by a panel of scientists and experts based on extensive research, the following Dietary Reference Intakes (DRIs) ensure that consumption of nutrient at the recommended amounts will meet the needs of nearly all healthy Americans. The DRIs are classified by age, gender, level of physical activity and life course to accommodate temporary needs due to for example, pregnancy and lactation.

Note: You can download these DRI tables in an Excel file: DRI Table [.xlsx].

On the Nutrition Frontier

Traditionally, we teach nutrition from a micro-perspective. What are all the individual nutrients, the exact amounts recommended, food sources, etc. This made sense when so many of our nutrition-related diseases were due to a deficiency of something. For example, scurvy is a deficiency disease where the body lacks enough vitamin C. Pellagra is a deficiency disease caused by insufficient intake of the B vitamin, niacin. Looking at specific nutrients is referred to as a 'reductionist' approach to nutrition. Yet, in North America, we are much less likely to see these frank deficiency diseases.