1.4: Overview of Nutrients and Calories

Learning Objectives

• Define the word “nutrient”.
• Identify the six classes of nutrients essential for health.
• List the three main energy (calorie) yielding nutrients and how many calories each of these nutrients provide.

What are Nutrients?

Nutrients are chemical substances found in food that are required by the body to provide energy, give the body structure, and help regulate chemical processes. There are six classes of essential nutrients required for the body to function and maintain overall health. These six classes of essential nutrients are: carbohydrates, lipids (fats), proteins, water, vitamins, and minerals.

Nutrients can be further classified as either macronutrients or micronutrients and either organic or inorganic, as well as whether or not they provide energy to the body (energy-yielding). We'll discuss these different ways of classifying nutrients in the following sections.

Foods also contain non-nutrients. Some non-nutrients appear to be very important for human health, like fiber and antioxidants; other non-nutrients may be harmful to human health such as preservatives, colorings, flavorings and pesticide residues.

Table \(\PageIndex{1}\): Six Classes of Nutrients and Their Functions

Nutrient	Functions
Carbohydrates	Provide a ready source of energy for the body (sometimes referred to as the preferred source of energy for the body). Provide structural constituents for the formation of cells.
Lipids (Fats)	Provide stored energy for the body. Function as structural components of cells and also as signaling molecules for proper cellular communication. Provide insulation to vital organs and works to maintain body temperature.
Proteins	Necessary for tissue formation, cell repair, regulating fluid balance, and hormone and enzyme production. Essential for building strong muscles and a healthy immune system.
Water	Transports essential nutrients to all body parts, transports waste products for disposal, and aids with body temperature maintenance.
Vitamins	Regulate body processes and promote normal body-system functions.
Minerals	Regulate body processes, are necessary for proper cellular function, and comprise body tissue.

Macronutrients

Nutrients that are needed in large amounts are called macronutrients. Macronutrients include carbohydrates, lipids (fats), proteins, and water. Carbohydrates, lipids, and proteins provide energy (calories) which can be used ("burned") by your body to perform basic functions. The energy from these macronutrients comes from their chemical bonds. This chemical energy is converted into cellular energy that is then utilized to perform work, allowing our bodies to conduct their basic functions. Water is needed in large quantities but does not contain energy (calories).

Carbohydrates

The major food sources of carbohydrates are grains, dairy products, fruits, and starchy vegetables like potatoes. Non-starchy vegetables also contain carbohydrates, but in lesser quantities. When you eat a food that contains carbohydrate, like bread for example, you receive approximately 4 calories of energy for every gram of carbohydrate you eat. Chemically speaking, carbohydrates are molecules composed of carbon, hydrogen, and oxygen. Carbohydrates are the preferred source of energy (calories) for your body.

Lipids (Fats)

Lipids (fats) are found predominately in butter, oils, meats, dairy products, nuts, seeds, and in many processed foods. Lipids provide more energy per gram than carbohydrates (9 calories per gram of lipids versus 4 calories per gram of carbohydrates). Lipids are also a family of molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. The main job of lipids is to store energy (calories) for later use. In addition to energy storage, lipids surround and protect organs, aid in temperature regulation, and regulate many other functions in the body.

Proteins

Major food sources of proteins include meats, dairy products, seafood, and a variety of different plant-based foods (e.g., soy). Proteins are macromolecules composed of chains of subunits called amino acids. Amino acids are composed of carbon, hydrogen, oxygen, and nitrogen. Proteins provide 4 calories of energy per gram; however providing energy is not protein’s most important function. Proteins provide structure to bones, muscles and skin, and play a role in conducting most of the chemical reactions that take place in the body.

Water

There is one other nutrient that we must have in large quantities: water. Water does not contain carbon, but is composed of two hydrogen atoms and one oxygen atom per molecule of water. Unlike the energy-yielding macronutrients (carbohydrates, lipids, and protein), water does not provide any energy (calories). More than 60 percent of your total body weight is water. Without it, nothing could be transported in or out of the body, chemical reactions would not occur, organs would not be cushioned, and body temperature would fluctuate widely.

Micronutrients

Micronutrients are nutrients required by the body in lesser amounts, but are still essential for carrying out bodily functions. Micronutrients include all the essential vitamins and minerals. There are 13 essential vitamins and 16 essential minerals (Tables \(\PageIndex{2}\) and \(\PageIndex{3}\) for a complete list and their major functions). In contrast to carbohydrates, lipids, and proteins, micronutrients do not contain calories. This is often confusing because most people have heard how tired a person will feel if they are low in a micronutrient such as Iron. The tiredness can be explained by the fact that, micronutrients assist in the process of making energy by being part of enzymes (i.e., coenzymes). Enzymes catalyze (cause or speed up) chemical reactions in the body and are involved in many aspects of body functions from producing energy, to digesting nutrients, to building macromolecules.

Vitamins

The thirteen vitamins are categorized as either water-soluble or fat-soluble. The water-soluble vitamins are vitamin C and all the B vitamins, which include thiamin, riboflavin, niacin, pantothenic acid, pyroxidine, biotin, folate and cobalamin. The fat-soluble vitamins are A, D, E, and K. Vitamins are required to perform many functions in the body such as making red blood cells, synthesizing bone tissue, and playing a role in normal vision, nervous system function, and immune system function.

Table \(\PageIndex{2}\): Vitamins and Their Major Functions

Vitamins	Major Functions
Water-soluble
B1 (thiamin)	Coenzyme, energy metabolism assistance
B2 (riboflavin)	Coenzyme, energy metabolism assistance
B3 (niacin)	Coenzyme, energy metabolism assistance
B5 (pantothenic acid)	Coenzyme, energy metabolism assistance
B6 (pyroxidine)	Coenzyme, amino acid synthesis assistance
Biotin	Coenzyme
Folate	Coenzyme, essential for growth
B12 (cobalamin)	Coenzyme, red blood cell synthesis
C	Collagen synthesis, antioxidant
Fat-soluble
A	Vision, reproduction, immune system function
D	Bone and teeth health maintenance, immune system function
E	Antioxidant, cell membrane protection
K	Bone and teeth health maintenance, blood clotting

The following video provides a nice overview of vitamins:

Video \(\PageIndex{1}\): How do vitamins work? - Ginnie Trinh Nguyen. Available at https://youtu.be/ISZLTJH5lYg

Minerals

Minerals are solid inorganic substances that form crystals and are classified depending on how much of them we need. Trace minerals, such as molybdenum, selenium, zinc, iron, and iodine, are only required in a few milligrams or less and macrominerals, such as calcium, magnesium, potassium, sodium, and phosphorus, are required in hundreds of milligrams. Many minerals are critical for enzyme function, others are used to maintain fluid balance, build bone tissue, synthesize hormones, transmit nerve impulses, contract and relax muscles, and protect against harmful free radicals.

Table \(\PageIndex{3}\): : Minerals and Their Major Functions

Minerals	Major Functions
Macro
Sodium	Fluid balance, nerve transmission, muscle contraction
Chloride	Fluid balance, stomach acid production
Potassium	Fluid balance, nerve transmission, muscle contraction
Calcium	Bone and teeth health maintenance, nerve transmission, muscle contraction, blood clotting
Phosphorus	Bone and teeth health maintenance, acid-base balance
Magnesium	Protein production, nerve transmission, muscle contraction
Sulfur	Protein production
Trace
Iron	Carries oxygen, assists in energy production
Zinc	Protein and DNA production, wound healing, growth, immune system function
Iodine	Thyroid hormone production, growth, metabolism
Selenium	Antioxidant
Copper	Coenzyme, iron metabolism
Manganese	Coenzyme
Fluoride	Bone and teeth health maintenance, tooth decay prevention
Chromium	Assists insulin in glucose metabolism
Molybdenum	Coenzyme

Vitamin and mineral deficiencies can cause severe health problems. For example, a deficiency in vitamin A can lead to night blindness. Anemia, a condition where there aren't enough healthy red blood cells to carry adequate oxygen throughout the body, can result from an iron deficiency.

Energy-Yielding Nutrients

The macronutrients—carbohydrate, protein, and fat—are the only nutrients that provide energy to the body. The energy from macronutrients comes from their chemical bonds. This chemical energy is converted into cellular energy that can be utilized to perform work, allowing cells to conduct their basic functions. Although vitamins also have energy in their chemical bonds, our bodies do not make the enzymes to break these bonds and release this energy. (This is fortunate, as we need vitamins for their specific functions, and breaking them down to use for energy would be a waste.)

Food energy is measured in kilocalories (kcals). A kilocalorie is the amount of energy needed to raise 1 kilogram of water by 1 degree Celsius. The kilocalories stored in food can be determined by putting the food into a scientific instrument called a bomb calorimeter and measuring the energy output (energy = heat produced).

In the US, the kilocalorie (kcal) is the most commonly used unit of energy and is often just referred to as a calorie. Strictly speaking, a kcal is 1000 calories. In nutrition, the term calories almost always refers to kcals. Sometimes the kcal is indicated by capitalizing calories as “Calories.” For the sake of simplicity, we’ll use the terms “calories” and “kilocalories” interchangeably in this book.

Below is a list of energy sources in the diet from lowest to highest calories per gram (a gram is about the weight of a paperclip). Notice the addition of alcohol. Although alcohol does provide energy, it isn’t a nutrient, because it isn’t required as a source of nourishment to the body.

Energy Sources (kcal/g)

• Carbohydrates 4
• Protein 4
• Alcohol 7
• Lipids 9

Carbohydrates and proteins provide 4 calories per gram, and fats provide 9 calories per gram. Fat is the most energy-dense nutrient, because it provides the most calories per gram (more than double carbohydrates and protein).

Figure \(\PageIndex{1}\): “FDA Nutrition Facts Label” by USDA Food and Drug Administration is in the Public Domain

Example \(\PageIndex{1}\): How to calculate the energy available from foods

When you look at the Nutrition Facts panel on a food label, 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.

Looking at the values in the Nutrition Facts label, you can convert grams into calories by doing the following calculations:

• 8 grams of fat x 9 kcal/g = 72 kcals
• 37 grams of carbohydrate x 4 kcal/g = 148 kcals
• 3 grams of protein x 4 kcal/g = 12 kcals

You can double check your math by adding the calories per serving provided from fat, carbohydrate, and protein. This number should come close to the total calories per serving listed on the Nutrition Facts. It will not always match up exactly (like in this example) due to rounding.

• 72 kcals from fat + 148 kcals from carbohydrate + 12 kcals from protein = 232 kcals total

Example \(\PageIndex{2}\): How to calculate the percentage of the total energy provided by one nutrient

Using the information listed in the previous example, you can calculate the percentage of the total kcalories that are provided by each of the nutrients in the food: carbohydrate, protein, and fat. For example, to find the percentage of kcalories from fat in the food, divide the kcals from fat by the total kcalories. You can round this number to two decimal places for simplicity.

• 72 kcals from fat / 232 kcals total = 0.31

Next, multiply by 100 to find the percentage.

• 0.31 x 100 = 31%

In this example, 31% of the total calories in the food were contributed by fat. Dietary recommendations suggest that 20 to 35% of your daily calories come from fat, 10 to 35% from protein, and 45 to 65% from carbohydrates.¹ These recommendations refer to the total energy intake for each day, not from individual foods. However, it can be useful to understand the contribution that each nutrient makes as you consider food choices for a well-balanced diet.

Video \(\PageIndex{2}\): What is a calorie? - Emma Bryce. Available at https://youtu.be/VEQaH4LruUo

Organic and Inorganic Nutrients

So far, we’ve categorized nutrients as macronutrients or micronutrients and based on whether or not they’re energy-yielding. There is one more way to categorize nutrients: organic or inorganic. When you think of the word “organic,” you might think of how foods are produced (with or without synthetic fertilizers and pesticides), but in this case we are referring to the chemical structure of a nutrient.

Organic Nutrients

The organic nutrients include the macronutrients (carbohydrate, protein, and fat) and vitamins. An organic nutrient contains both carbon and hydrogen. Organic nutrients can be made by living organisms and are complex, made up of many elements (carbon, hydrogen, oxygen, and sometimes nitrogen) bonded together. In a sense, they are “alive,” and therefore can be destroyed or broken down.

Vitamin E (shown below) is an organic molecule, because it contains both carbon and hydrogen atoms. Vitamin E is synthesized by plants and can be destroyed by heat during cooking.

Figure \(\PageIndex{2}\): “Vitamin E” by Annabel is licensed under CC BY-SA 3.0

Inorganic Nutrients

Inorganic nutrients include both water and minerals. Inorganic nutrients do not contain both carbon and hydrogen, and they are not created or destroyed. Minerals can’t be destroyed, so they are the ash left when a food is burned to completion. Minerals are also not digested or broken down, as they are already in their simplest form. They are absorbed as-is, then shuttled around the body for their different functions, and then excreted.

Figure \(\PageIndex{3}\): "Skeletal Structure of Water" by TSOL is licensed under CC BY-SA 4.0

Summary

The different categories of nutrients are summarized in the following table.

Table \(\PageIndex{4}\): “Summary of classification of nutrients” by Tamberly Powell is licensed under CC BY-NC-SA 4.0

Classification	Nutrient
Macronutrient	Carbohydrate, protein, lipids, water
Micronutrient	Vitamins, minerals
Energy-Yielding	Carbohydrate, protein, fat
Organic	Carbohydrate, protein, lipids, vitamins
Inorganic	Minerals, water

Key Takeaways

• Foods contain nutrients that are essential for our bodies to function.
• Four of the classes of nutrients required for bodily function are needed in large amounts. They are carbohydrates, lipids, proteins, and water, and are referred to as macronutrients.
• Two of the classes of nutrients are needed in lesser amounts, but are still essential for bodily function. They are vitamins and minerals.
• The "energy yielding" nutrients are carbohydrates, lipids (fats), and proteins. Carbohydrates provide 4 calories for every gram we consume; fats provide 9 calories for every gram we consume; and proteins provide 4 calories for every gram we consume.

Attributions

• Introduction to Nutrition by Ann Diker. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Available at: https://med.libretexts.org/Courses/Metropolitan_State_University_of_Denver/Introduction_to_Nutrition_(Diker)
• Nutrition: Science and Everyday Application by Alice Callahan, PhD, Heather Leonard, MEd, RDN, and Tamberly Powell, MS, RDN is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted. Available at: https://openoregon.pressbooks.pub/nutritionscience/

References

1. Food and Nutrition Board of the Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. (Washington, DC: National Academies Press, 2005).

Learning Check \(\PageIndex{1}\)