Every bite of food you eat contains hundreds of substances, including nutrients that provide energy, support growth and repair, and help regulate body processes. Foods also contain other naturally occurring substances that are not classified as nutrients. These include phytochemicals  from plants and zoochemicals from animal foods. While these substances are not required for life, as are nutrients, many provide health benefits.

What Are Nutrients?

Nutrients are components of food that your body needs for energy, growth, repair, and the regulation of body processes. Every breath you take, every thought you think, every movement you make, and every wound that heals depends on the nutrients you consume.

Nutrition scientists classify nutrients in three primary ways: 1) the amount needed, 2) whether they provide energy, and 3) their chemical makeup, as outlined below.

Macronutrients: Carbohydrates, Lipids, Proteins, and Water 

Macronutrients are nutrients the body needs in relatively large amounts. They include carbohydrates, proteins, lipids (fats), and water. Carbohydrates, proteins, and fats provide energy (calories), while water is required in large amounts to support essential body functions, even though it does not provide calories.

Figure 2.6 illustrates the four macronutrients, their basic chemical structures, and common food sources. Table 2.4 summarizes their recommended intakes and primary functions.

Energy-Yielding Nutrients: Carbohydrates, Proteins, and Fats

Carbohydrates, proteins, and fats are called energy-yielding nutrients because they supply the calories your body uses for movement, growth, repair, and other body functions.

In contrast, vitamins, minerals, and water do not provide calories. Instead, they help the body use energy and function properly.

Food energy is measured in kilocalories (kcal), commonly called calories on food labels. Scientists can measure the energy content of food using a device called a bomb calorimeter, which determines the amount of heat released when a food sample is burned (Figure 2.7).

In the United States, the kilocalorie (kcal) is the most commonly used unit of food energy and is often simply called a calorie. Strictly speaking, one kilocalorie equals 1,000 calories. However, on Nutrition Facts labels and in everyday conversation, the term calorie almost always refers to a kilocalorie. For simplicity, this book uses the terms calorie and kilocalorie interchangeably.

Table 2.5 shows the energy provided by macronutrients and alcohol. Notice that alcohol provides energy but is not considered a nutrient because it is not required by the body for growth, maintenance, or health.

Carbohydrates and proteins provide 4 calories per gram, while fats provide 9 calories per gram, making fat the most energy-dense nutrient.

When you look at the Nutrition Facts panel on a food label (Figure 2.8), you’ll see that it lists calories, as well as grams of total fat, total carbohydrates, and protein per serving. From these values, you can estimate the amount of calories coming from the different macronutrients.

To calculate the calories contributed by each macronutrient, multiply the number of grams by its energy value: fat provides 9 kcal per gram, while carbohydrates and protein provide 4 kcal per gram (Table 2.6).

You can check your calculation by adding the calories provided by fat, carbohydrates, and protein. The total should be close to the number of calories listed on the Nutrition Facts label. However, the values may not match exactly because manufacturers are allowed to round nutrient and calorie values on food labels.

Organic vs. Inorganic Nutrients

So far, nutrients have been classified according to the amount the body needs and whether they provide energy. They can also be classified by their chemical structure as either organic or inorganic.

ORGANIC NUTRIENTS

In nutrition, the term “organic” has two distinct meanings. In chemistry, organic refers to substances that contain carbon. For example, vitamin E is an organic nutrient because its chemical structure contains carbon atoms, as shown in Figure 2.6a.

In the food industry, however, organic certification describes how foods are grown or raised according to specific agricultural standards. This use of the term has nothing to do with a nutrient’s chemical composition.

INORGANIC NUTRIENTS

Inorganic nutrients include water and minerals. Unlike organic nutrients, inorganic nutrients do not contain both carbon and hydrogen. Minerals are chemically simple and cannot be destroyed by cooking or digestion. They are absorbed as-is and used by the body for a variety of important functions.

Table 2.7 summarizes the differences between organic and inorganic nutrients.

Attributions

This section is an adaptation of “Classification of Nutrients” in Nutrition: Science and Everyday Application, V. 1.0 by Alice Callahan, PhD; Heather Leonard, MEd, RDN; and Tamberly Powell, MS, RDN under a Creative Commons Attribution-NonCommercial 4.0 International License.