Chapter 1: Introduction to Nutrition

Learning Objectives

By the end of this chapter, you will be able to:

• Define nutrient.
• Describe nutrients as chemicals.
• Describe the classes of nutrients.
• Define calorie and kilocalorie (kcal).
• Calculate number of kcals in carbohydrates, proteins, and fats.
• Use metric prefixes and basic metric units of measure relevant to nutrition.
• Convert between different measurement units important in nutrition.

Why Study Nutrition?

Our food choices – what we eat, when we eat and how much we eat – play important roles in our life by affecting our health, celebrating our heritage, and providing the centerpiece of many social interactions. Nutrition is the scientific study of the food we eat and how our body obtains, metabolizes, and uses nutrients from that food.

Adequate nutrition is required for humans to function. Deficits in energy or in essential nutrients can lead to disease, such as a lack of vitamin A can lead to blindness. Although diseases caused by lack of appropriate nutrition have decreased significantly over the past century, one fifth of all deaths worldwide are associated with poor diet ^[1]. Complex nutritional factors also contribute to chronic diseases such as diabetes, cardiovascular disease, some types of cancers, and liver. Billions of people worldwide are affected by health conditions related to nutrition ^[2].

What are Nutrients?

Nutrients are chemicals the body needs to perform its basic functions. We obtain these chemicals from our food. Nutrients provide energy, form the building blocks of our biomolecules, and regulate chemical processes in the body. These basic functions allow us to detect and respond to environmental surroundings, move, excrete wastes, respire (breathe), grow, and reproduce. There are six classes of nutrients: carbohydrates, lipids, proteins, water, vitamins, and minerals. Foods also contain non-nutrients that may be beneficial (such as antioxidants) or harmful (such as natural toxins found in plant foods and additives such as dyes and preservatives).

It may be surprising to think of nutrients as chemicals. The word ‘chemical’ can be misrepresented in everyday usage as a substance that is artificial or somehow bad for us. In reality, everything that has mass and takes up space is made of chemicals. We are made up of chemicals! Those chemicals are organized into the cells that make up our tissues and organs. The air we breathe and our food are made of chemicals. Much of what we will be studying over this quarter is what those chemicals are and how the body uses them.

Macronutrients

Nutrients that are needed in large amounts are called macronutrients. The three classes of macronutrients – carbohydrates, lipids, and proteins – provide raw materials to build body structures as well as energy to power the body. The energy contained in food is converted into cellular energy that allows the body to grow, heal, and perform work.

The amount of energy we obtain from food is measured in units called calories. A calorie (c) is the amount of energy that is required to increase the temperature of one gram of water by one degree Celsius. This is a small amount of energy, and bodies need hundreds of thousands of these calories per day. In nutrition conversations and food labels, therefore, energy in food is presented in “Calories” (with a capital C), which is equivalent to one thousand “small c” calories. Another name for a nutritional Calorie is kilocalorie (kcal); kilo- is a prefix that means one thousand in the metric system. In nutrition, nutrients are often measured in metric units including grams and milligrams. It is safe to assume when reading nutrition sources and food labels that energy in food is expressed in kcals and NOT in “small c” calories. The end of the chapter has some guidance about metric prefixes and their meanings.

Carbohydrates, lipids, and proteins are chemicals that have a carbon atom as a core component and also contain hydrogen. This defines them as organic chemicals. Organic chemicals generally originate inside of living things. Note this use of the word “organic” for types of chemicals is different from how it is used when we talk about “organic foods” from a market! Inorganic chemicals include water, salts, and other minerals that are commonly found outside of living organisms. Inorganic chemicals do not yield energy for the body.

Water is the only inorganic chemical that is also a macronutrient in the sense that you require a large amount of it. However, because it is inorganic, it does not provide energy to the body.

Carbohydrates

Carbohydrates are molecules that provide energy and are composed of carbon, hydrogen, and oxygen. The major food sources of carbohydrates are grains, milk, fruits, and starchy vegetables, like potatoes. Non-starchy vegetables also contain carbohydrates, but in lesser quantities. Carbohydrates are broadly classified into two forms based on their chemical structure: simple carbohydrates, often called sugars; and complex carbohydrates.

Simple carbohydrates consist of one or two basic units, or monomers. Examples of simple sugars include sucrose, the type of sugar you find in a sugar packet at the coffee shop, and glucose, the type of sugar that circulates in your blood.

Complex carbohydrates are long branched or unbranched chains of sugar monomers. During digestion, the body breaks down digestible complex carbohydrates to simple sugars, mostly glucose. Glucose is transported to all our cells where it is stored, used to make energy, or used to build macromolecules. Fiber is also a complex carbohydrate, but it cannot be broken down by human digestive enzymes in the intestines. As a result, it passes through the digestive tract undigested by human enzymes. Bacteria that inhabit the intestines break down some types of fiber.

One gram of digestible carbohydrates yields four kilocalories of energy for the cells in the body to perform work. In addition to providing energy and serving as building blocks for bigger macromolecules, carbohydrates are essential for proper functioning of the nervous system, heart, and kidneys. Glucose can be stored for use by the body between meals. In humans, glucose is stored in the liver and muscles as a huge molecule called glycogen; in plants, glucose is stored as starch. Glycogen and starch are both complex carbohydrates, but note that only animals make glycogen and only plants make starch.

Lipids

Molecules in the lipid family are also composed of carbon, hydrogen, and oxygen. An important characteristic of lipids is that they do not dissolve in water. They include familiar greasy and oily substances such as cooking oil and butter but are also found in other substances that might be surprising.

Lipids are produced by animals and plants. Animal-based foods such as meat, dairy products, and eggs are rich sources of lipids. Plant-based foods such as nuts, seeds, and some fruits (e.g. avocadoes) are also sources of lipids. Many processed foods contain lipids, especially in the form of oil, butter, or lard.

The three main types of lipids are triglycerides (triacylglycerols, often termed fats), phospholipids, and sterols. The main jobs of lipids in humans are to be broken down to produce energy and to store energy in adipose (fat) tissue. Lipids provide more energy per gram than carbohydrates: one gram of fat provides nine kilocalories of energy. In addition to storing energy, lipids are a major component of cell membranes, surround and protect organs, provide insulation, and regulate many other functions in the body.

Proteins

The third type of macronutrients, proteins, are also composed of carbon, oxygen, and hydrogen, and contain an important new component: nitrogen. Eating protein is important for animals to obtain the nitrogen their bodies need.

Proteins are made of twenty different types of amino acid monomers, which are the building blocks of proteins. Instructions for making new proteins in cells are contained in the DNA sequences organisms inherit from parents. An important reason to eat sufficient protein is to ensure that the body has enough amino acids for maintenance and growth. While all plants and animals make proteins, rich dietary sources of protein include meats, dairy products, seafood, and plant-based foods such as soy. The word protein comes from a Greek word meaning “of primary importance,” which is an apt description of these macronutrients. Proteins provide four kilocalories 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 chemical reactions in the body.

Water

Water is another nutrient that we must have in large quantities. Water does not contain carbon but is composed of two hydrogens and one oxygen per molecule. More than 60 percent of 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. On average, an adult consumes just over two liters of water per day from food and drink combined. Water is critical for life’s basic processes. Importantly, water does not contain calories.

Micronutrients

Micronutrients, which include the vitamins and minerals, are nutrients required by the body in small amounts. We frequently hear the phrase “essential vitamins and minerals;” essential” is a word used in nutrition to indicate that a substance cannot be made by the body in sufficient quantities and must be taken in through food and drink. In contrast to carbohydrates, lipids, and proteins, micronutrients do not provide energy (kcals). Their important functions include assisting in body processes as components of enzymes, sometimes called cofactors or coenzymes. Enzymes are proteins that catalyze chemical reactions in the body and are involved in body functions including energy production, digestion, and building body structures. Without vitamins and minerals, these functions would be impaired or impossible. Additionally, micronutrients regulate water balance and defend the body against disease.

What is the difference between vitamins and minerals? Vitamins are organic chemicals that contain carbon and hydrogen and originate in living cells. Minerals are inorganic chemicals that can come from the environment. For example, sea salt can be purified from ocean water (Figure 1.3). One difference between organic and inorganic compounds is the stability of the compounds in food. Heat, light, and exposure to oxygen can degrade vitamins, but minerals are resistant to these environmental assaults. Therefore, cooking can destroy vitamins, while minerals can retain their functions even if heated. Both vitamins and minerals can leach into water if food is soaked or boiled.

Minerals

Minerals, the inorganic micronutrients, are classified by how much we need. Trace minerals, such as molybdenum, selenium, zinc, iron, and iodine, are required in small amounts, typically less than 100 mg per day. Major minerals, sometimes called macrominerals, include calcium, magnesium, potassium, sodium, and phosphorus. The daily requirement for these is over 100 milligrams per day.

Some minerals are critical for enzyme function, others are used to maintain fluid balance, build bones and teeth, synthesize hormones, transmit nerve impulses, contract and relax muscles, and protect against harmful free radicals in the body that can cause health problems such as cancer.

Major Minerals and Their Important Functions

• Sodium: Fluid balance, nerve transmission, muscle contraction
• Chloride: Fluid balance, stomach acid
• Potassium: Fluid balance, nerve transmission, muscle contraction
• Calcium: Bone and tooth health, nerve transmission, muscle contraction, blood clotting
• Phosphorus: Bone and tooth health, acid-base balance, DNA structure
• Magnesium: Protein production, nerve transmission, muscle contraction

Trace Minerals and Their Important Functions

• Iron: Oxygen transport, 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 for many functions
• Fluoride: Bone and tooth health, tooth decay prevention

Vitamins

Vitamins are organic chemicals, they contain carbon and hydrogen as important components. As organic chemicals, vitamins are made by living organisms including microbes, plants, and animals. Importantly, vitamins can be destroyed during food storage or cooking.

The thirteen vitamins are categorized as either water-soluble or fat-soluble. The water-soluble vitamins are vitamin C and the B vitamins, which include thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, 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 bones, and maintaining healthy function of the vision, nervous, and immune systems.

Vitamin deficiencies can cause severe health problems and even death. For example, a deficiency in niacin causes a disease called pellagra, which was common in the early twentieth century in some parts of America. The common signs and symptoms of pellagra are the “4D’s—diarrhea, dermatitis, dementia, and death.” Until scientists determined that better diets relieved the pellagra, many people with the disease ended up in insane asylums awaiting death. Other vitamins were found to prevent specific disorders and diseases such as scurvy (vitamin C), night blindness (vitamin A), and rickets (vitamin D).

Water-Soluble Vitamins and Their Important Functions

• Thiamin (B1): Coenzyme in energy production pathways
• Riboflavin (B2): Coenzyme in energy production pathways
• Niacin (B3): Coenzyme in energy production pathways
• Pantothenic acid (B5): Coenzyme in energy production pathways
• Pyridoxine (B6): Coenzyme in amino acid synthesis
• Biotin (B7): Coenzyme, amino acid and fatty acid metabolism
• Folate (B9): Coenzyme, essential for DNA synthesis, cell division and growth
• Cobalamin (B12): Coenzyme, red blood cell synthesis
• Ascorbic acid (C): Collagen synthesis, antioxidant

Fat-Soluble Vitamins and Their Important Functions

• A: Vision, reproduction, immune system function, antioxidant
• D: Bone and tooth health, immune system function
• E: Antioxidant, cell membrane protection
• K: Bone and tooth health, blood clotting

Nutrients Summary

In summary, nutrients can be categorized as macronutrients or micronutrients based on the amount our body needs. The major classes of macronutrients are the organic, energy-producing carbohydrates, proteins, and lipids as well as the inorganic, non-energy-producing water. Micronutrients, which do not produce energy, include organic vitamins and inorganic minerals.

Nutrients and Their Important Functions

• Protein: Necessary for tissue formation, cell repair, hormone and enzyme production. Essential for building strong muscles and a healthy immune system.
• Carbohydrates: Provide a ready source of energy for the body and provide structural constituents of cells.
• Fats: Stored energy in the body. Function as structural component of cells and signaling molecules for cell communication. Provide insulation and cushion organs.
• Vitamins: Regulate many body processes.
• Minerals: Regulate body processes, are necessary for proper cellular function, and comprise body tissue.
• Water: Transports nutrients and oxygen throughout the body, transports waste products for disposal, and aids with body temperature maintenance.

Units of Measure

Nutritionists, as well as other scientists, use the metric system, which we will use in this class. The work for nutritionists is complicated because most people in the U.S. do not use the metric system, instead using traditional units likes cups and ounces.

The units we use the most in nutrition are mass (for human weights as well as for food quantity), volume (for food quantity), and length (for human height). Food safety discussions include temperature.

Common Metric System Prefixes and Their Meanings

Metric measurements use prefixes to convert between units. A kilogram is 1000 grams. A milligram is 1/1,000 of a gram. A microgram is 1/1,000 of a milligram (or 1/1,000,000 of a gram). Common prefixes you should know follow.

• Micro- (μ) = 1/1,000,000th (one millionth)
• Milli- (m) = 1/1000th (one thousandth)
• No prefix = Base unit
• Kilo- (k) = 1000x (one thousand times)

Mass

Food packages may show ounces and pounds. The weight may also be shown in grams, or the grams can be calculated using the conversion factor below. Nutrients are usually weighed in grams for macronutrients or milligrams and micrograms for micronutrients. People usually weigh themselves in pounds in the U.S. As you can see, knowing different units and conversion factors can be helpful.

Common Units of Mass and Conversion Factors

Metric system mass units

• Microgram (μg or mcg)
• Milligram (mg)
• Gram (g)
• Kilogram (kg)

US customary system mass units

• Ounce (oz)
• Pound (lb)

US/metric mass conversion factors

• 1 oz = 28.35 g
• 1 lb = 16 oz
• 1 lb = 454 g
• 1 kg = 2.2 lbs

Volume

Milliliters and liters are common units for volumes of food and beverages. In the US, you are likely to encounter liquids measured in fluid ounces, cups, quarts, and gallons.

Common Units of Volume and Conversion Factors

Metric system volume units

• Milliliter (mL)
• Liter (L)

US customary system volume units

• Fluid ounce (fl oz)
• Cup (c) = 8 fl oz
• Quart (qt) = 4 c
• Gallon (gal) = 4 qt

US/metric volume conversion factors

• 1 fl oz = 2 tbsp = 29.6 mL
• 1 c = 8 fl oz = 237 mL
• 1 qt = 0.95 L
• 1 gal = 3.7 L

Length

Height or length are usually expressed in meters, though in the US inches and feet are still common.

Common Units of Volume and Conversion Factors

Metric system length units

• Millimeter (mm)
• Meter (m)

US customary system length units

• Inch (in)
• Foot (ft) = 12 in

US/metric length conversion factors

• 1 in = 25.4 mm
• 1 ft = 30.5 cm

Converting Between Units

For this course, we will convert between µg, mg and g; between mL and L, and between mm and m. For diet analysis, we will convert customary US units to their respective metric units: pounds to kilograms, ounces to grams, feet and inches to meters, fluid ounces or cups to milliliters, and so forth. In addition, we will calculate the kcals in foods containing various amounts of macronutrients.

Converting between units is called dimensional analysis, unit analysis or unit conversion. If you have had a chemistry class, you have done these types of calculations.

Converting between units relies on a simple fact of arithmetic: any number multiplied by one will be unchanged. We take advantage of this by multiplying the number we wish to convert by a ratio that is equal to one but with different units. This ratio is called a conversion factor. An example of a conversion factor is 12 inches/1 ft. Because there are twelve inches in one foot, a ratio of 12 inches/1 ft is equal to one and can be used as a conversion factor.

Note: Either 12 in/1 ft and 1 ft/12 in can be used, depending on the equation. Both conversion factors are equal to one.

To complete a dimensional analysis, use the following steps:

• Identify the value that is the given.
• Identify the unit you are converting to.
• Identify the conversion factor that will help you get from the original unit to the desired unit.
• Set up your equation with the conversion oriented such that the undesired units cancel out and you are left with the desired units. A unit cancels out if it appears in both the numerator and the denominator.
• Multiply through to reach the answer.
• You can use this method to convert between any units for which you have a conversion factor. Important conversions in nutrition include those for kilocalories and grams mentioned previously for the macronutrients: 4 kcal/g for carbohydrates and proteins, 9 kcal/g for lipids.

Dimensional Analysis Example 1

Here is an example problem: how many grams are in 3 ounces?

• Identify the given information: 3 ounces (oz.)
• Identify the unit converting to: grams (g)
• Identify the conversion factor(s) that will help you get from the original units to the desired unit:
• Set up an equation so that the original units cancel out to leave the desired units:
• Multiply through to get the final answer:

Dimensional Analysis Example 2

Here is another example problem: how many grams of sugar would provide 300 kcal of energy?

• Identify the given information: 300 kcal
• Identify the unit converting to: g carb (since sugar is a carbohydrate)
• Identify the conversion factor(s) that will help you get from the original units to the desired unit:
• Set up an equation so that the original units cancel out to leave the desired units:
• Multiply through to get the final answer:

References

1. GBD 2017 Diet Collaborators. “Health effects of dietary risks in 195 countries, 1990–2017: a systematic analysis for the Global Burden of Disease Study” 2019. The Lancet. DOI: 10.1016/S0140-6736(19)30041-8.
2. Malnutrition. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/malnutrition/. Updated March 1, 2024. Accessed March 5, 2026.

Attributions

Adapted by Pattie S. Green, Ph.D. and Jonathan Pottle , Ph.D., Tacoma Community College, from the following sources:

• Macronutrient and Micronutrient sections adapted from Human Nutrition, Chapter 1 Introduction, by University of Hawai‘i at Mānoa Food Science and Human Nutrition Program, which is licensed under a Creative Commons Attribution 4.0 International License
• Converting Between Units sections adapted from Introductory Chemistry, 6. Dimensional Analysis, by Utah State University, which is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.