An Introduction to Nutrients

What are Nutrients?

Food refers to the plants and animals that we consume. The foods we eat contain nutrients. Nutrients are substances required by the body to perform its basic functions. Nutrients must be obtained from our diet since the human body does not synthesize or produce them. Nutrients have one or more of three basic functions: they provide energy, contribute to body structure, and/or 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 required for the body to function and maintain overall health. These are carbohydrates, lipids, proteins, water, vitamins, and minerals (see Table 1.3 for a summary of their functions). Foods also contain non-nutrients that may be harmful (such as natural toxins common in plant foods and additives like some dyes and preservatives) or beneficial (such as antioxidants and phytochemicals).

Organic vs. Inorganic Nutrients

Nutrients can be described as organic or inorganic. When a nutrient is described as organic, it means that it contains carbon while an inorganic nutrient does not contain carbon. Carbohydrates, lipids, proteins and vitamins are organic, whereas minerals and water are inorganic.

Macronutrients

Nutrients that are needed in large amounts are called macronutrients. There are three classes of macronutrients: carbohydrates, lipids, and proteins. Macronutrients are also used to produce energy, which is our capacity to perform work. Carbohydrates, lipids and proteins can be metabolically processed into cellular energy, and this energy 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. In food, energy can be measured in calories. On nutrition food labels, the amount given for “calories” actually refers to kilocalories (Kcal), which is equivalent to each calorie multiplied by one thousand. Water is also a macronutrient in the sense that you require a large amount of it, but unlike the other macronutrients, it does not yield calories.

Carbohydrates

Carbohydrates are molecules composed of carbon, hydrogen, and oxygen. The primary food sources of carbohydrates are grains, milk, fruits, and starchy vegetables like potatoes. For example, traditional Asian diets often include rice as a significant source of carbohydrates, while Latin American cuisines feature corn-based foods like tortillas. These examples demonstrate the diverse array of carbohydrate-rich foods across different cultures.

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 simple sugars; and complex carbohydrates.

Simple carbohydrates consist of one or two basic units. Examples of simple sugars include sucrose, the type of sugar you would have in a bowl on the breakfast table, and glucose, the type of sugar that circulates in your blood.

Complex carbohydrates are long chains of simple sugars that can be unbranched or branched. During digestion, the body breaks down digestible complex carbohydrates into simple sugars, mostly glucose. Glucose is then transported to all our cells where it is stored, used to make energy, or used to build macromolecules. Fibre is also a complex carbohydrate, but it cannot be broken down by digestive enzymes in the human intestine. As a result, it passes through the digestive tract undigested unless the bacteria that inhabit the colon or large intestine break it down.

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 the proper functioning of the nervous system, heart, and kidneys. As mentioned, glucose can be stored in the body for future use. In humans, the storage molecule of carbohydrates is called glycogen, and in plants, it is known as starch. Glycogen and starch are complex carbohydrates.

Lipids

Lipids are also a family of molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. Lipids are found predominantly in butter, oils, meats, dairy products, nuts, and seeds, and in many processed foods. The three main types of lipids are:

1. Triglycerides (the most common lipid in food)
2. Phospholipids
3. Sterols

The main job of lipids is to provide or store energy. Lipids provide more energy per gram than carbohydrates (nine kilocalories per gram of lipids versus four kilocalories per gram of carbohydrates) and provide a higher proportion of energy during rest and low-intensity exercise. Lipids are the major form of stored energy and we store large amounts of triglycerides as adipose tissue (body fat). In addition to energy storage, lipids are a major component of cell membranes, surround and protect organs (in fat-storing tissues), provide insulation to aid in temperature regulation and regulate many other functions in the body.

Proteins

Proteins are macromolecules composed of chains of subunits called amino acids. Amino acids are simple subunits composed of carbon, oxygen, hydrogen, and nitrogen. Food sources of proteins include meats, dairy products, seafood, and a variety of different plant-based foods, most notably soy. Proteins provide four kilocalories of energy per gram; however, providing energy is not protein’s most important function. We break down dietary proteins into amino acids and then reassemble them into bodily proteins that provide structure to bones, muscles and skin, support tissue growth, repair and maintenance, and play a role in conducting most of the chemical reactions that take place in the body. Scientists estimate that over 100,000 different proteins exist within the human body. The genetic codes in DNA are basically protein recipes that determine the order in which 20 different amino acids are bound together to make thousands of specific proteins.

A visual representation of the macronutrients: carbohydrates, lipids, protein, and water. The image shows four distinct sections, each labeled with the name of the macronutrient. The carbohydrates section depicts sources like grains, fruits, and vegetables. The lipids section displays sources such as oils. The protein section showcases sources like meat, and dairy products. Lastly, the water section represents a cup full of water. This image highlights the key macronutrients, and their importance in nutrition. 

Water

There is one other nutrient that we must have in large quantities: water. Water does not contain carbon, but is composed of two hydrogens and one oxygen per molecule of water. More than 60 percent of your total body weight is water. Water is involved in many bodily processes and 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. Specifically, water is involved in fluid balance and nutrient transport, nerve impulses, body temperature, muscle contractions, and excretion of waste products. On average, an adult consumes just over two litres of water per day from food and drinks combined. Since water is so critical for life’s basic processes, the amount of water input and output is supremely important.

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 minerals and vitamins. There are sixteen essential minerals and thirteen vitamins (See Table 1.1 “Minerals and their major functions” and Table 1.2 “Vitamins and their major functions” for a complete list and their major functions). In contrast to carbohydrates, lipids, and proteins, micronutrients are not sources of energy (calories), but they assist in the process as cofactors or components of enzymes (i.e., coenzymes). Enzymes are proteins that catalyze chemical reactions in the body and are involved in all aspects of bodily functions such as producing energy, digesting nutrients, and building macromolecules. Micronutrients play many essential roles in the body.

Minerals

Minerals are solid inorganic substances 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. Major minerals, such as calcium, magnesium, potassium, sodium, and phosphorus, are required in hundreds of milligrams. Many minerals are critical for enzyme function, while 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 in the body that can cause health problems such as cancer.

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 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 and synthesizing bone tissue, while also playing a role in normal vision, nervous system function, and immune system function.

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 known as the “4D’s—diarrhea, dermatitis, dementia, and death.” Until scientists discovered that better diets relieved the signs and symptoms of pellagra, many people with the disease ended up hospitalized in insane asylums, awaiting death. Other vitamins were also found to prevent certain disorders and diseases such as scurvy (vitamin C), night blindness (vitamin A), and rickets (vitamin D).