Define the word “nutrient” and identify the six classes of nutrients essential for health. List the three energy-yielding nutrients and their energy contribution.

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What is in Food?

The foods we eat contain nutrients. Those nutrients that contain carbon are called organic while those that do not contain carbon are called inorganic. Nutrients are substances required by the body to perform its basic functions. Since the human body does not synthesize nutrients, they must be obtained from the diet, making them essential. Eating inadequate amounts can cause poor health.

Nutrients are used to produce energy, 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. Foods also contain nonnutrients that may be harmful (such as cholesterol, dyes, and preservatives) or beneficial (such as phytochemicals like antioxidants and zoochemicals like omega-3 fatty acids).

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Figure 1.3.2: The Macronutrients: Carbohydrates, Lipids, Protein, and Water

Slow-releasing or complex carbohydrates are long chains of simple sugars that can be branched or unbranched. Starch is an example of a slow-releasing carbohydrate. During digestion, the small intestine breaks down all slow-releasing carbohydrates to simple sugars, mostly glucose. Glucose is then absorbed and transported to all our cells where it is stored in the form of glycogen, used to make energy, or used to build macromolecules. Fiber is also a slow-releasing carbohydrate, but it cannot be broken down in the human body and passes through the digestive tract undigested unless the bacteria that inhabit the gut break it down.

One gram of 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. 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 starches. Glycogen and starches are slow-releasing carbohydrates.


Lipids are also a family of molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. This class of molecules may be visible (for example vegetable oil) or invisible (for example, cream) in the food you eat. Lipids are found predominately in butter, oils, meats, dairy products, nuts, and seeds, and in many processed foods. The three main types of lipids are triglycerides (also called triacylglycerols), phospholipids, and sterols. The main job of lipids is to store energy. Lipids provide more energy per gram than carbohydrates (nine kilocalories per gram of lipids versus four kilocalories per gram of carbohydrates). In addition to energy storage, lipids serve as cell membranes, surround and protect organs, aid in temperature regulation, and regulate many other functions in the body. The main job of lipids is to store energy. Lipids provide more energy per gram than carbohydrates (nine kilocalories per gram of lipids versus four kilocalories per gram of carbohydrates). In addition to energy storage, lipids serve as cell membranes, surround and protect organs, aid in temperature regulation, and regulate many other functions in the body.


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. Without it, nothing could be transported in or out of the body, chemical reactions would not occur (acts as a solvent), organs would not be cushioned, joints would not be lubricated, and body temperature would fluctuate widely. On average, an adult consumes just over two liters of water per day from food and drink. According to the “rule of threes,” a generalization supported by survival experts, a person can survive three minutes without oxygen, three days without water, and three weeks without food. Since water is so critical for life’s basic processes, the amount of water input and output is supremely important, a topic we will explore in detail in Chapter 7.


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 thirteen vitamins and sixteen essential minerals (See Table 1.3.1 and Table 1.3.2 for a complete list and their major functions). In contrast to carbohydrates, lipids, and proteins, micronutrients are not directly used for making energy, but they assist in the process as being part of enzymes (i.e., coenzymes). Enzymes are proteins that catalyze chemical reactions in the body and are involved in all aspects of body functions from producing energy to digesting nutrients to building macromolecules. Micronutrients play many roles in the body.


The thirteen vitamins are organic compounds (carbon-based) 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, 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 (regulatory and metabolic capacity) such as making red blood cells, synthesizing bone tissue, and playing a role in normal vision, nervous system function, and immune system function. Some function in chemical reactions involved in the release of energy from carbohydrates, fat, protein, and alcohol. Vitamins do not supply energy directly and are not structural; they enable chemical reactions to occur.

Table 1.03.1: Vitamins and Their Major Functions Vitamins Major Functions
B1 (thiamine) 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
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

Vitamin deficiencies can cause severe health problems. 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 found out that better diets relieved the signs and symptoms of pellagra, many people with the disease ended up in insane asylums awaiting death (Video 1.3.1). Other vitamins were also found to prevent certain disorders and diseases such as scurvy (vitamin C), night blindness (vitamin A), and rickets (vitamin D).

Video 1.3.1: This video provides a brief history of Dr. Joseph Goldberger’s discovery that pellagra was a diet-related disease.

Video 1.03.2: This video describes a calorie. We hear about calories all the time: How many calories are in this cookie? How many are burned by doing 100 jumping jacks, or long-distance running, or fidgeting? But what is a calorie, really? And how many of them do we actually need? Emma Bryce explains how a few different factors should go into determining the recommended amount for each person.

One measurement of food quality is the amount of nutrients it contains relative to the amount of energy (Calories) it provides. High-quality foods are nutrient dense, meaning they contain lots of the nutrients relative to the amount of Calories they provide. Nutrient-dense foods are the opposite of “empty-calorie” foods such as carbonated sugary soft drinks, which provide many calories and very little, if any, other nutrients. Food quality is additionally associated with its taste, texture, appearance, microbial content, and how much consumers like it. The quantity of nutrients present in foods can be influenced by farming conditions, ripeness of plants when harvested, cooking processes, and length of time it is stored.

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Food: A Better Source of Nutrients

It is better to get all your micronutrients from the foods you eat as opposed to from supplements. Supplements contain only what is listed on the label, but foods contain many more macronutrients, micronutrients, and other chemicals, like antioxidants that benefit health. While vitamins, multivitamins, and supplements are a $20 billion industry in this country and more than 50 percent of Americans purchase and use them daily, there is no consistent evidence that they are better than food in promoting health and preventing disease. Dr. Marian Neuhouser, associate of the Fred Hutchinson Cancer Research Center in Seattle, says that “…scientific data are lacking on the long-term health benefits of supplements. To our surprise, we found that multivitamins did not lower the risk of the most common cancers and also had no impact on heart disease.”Woodward, K. “Multivitamins Each Day Will Not Keep Common Cancers Away; Largest Study of Its Kind Provides Definitive Evidence that Multivitamins Will Not Reduce Risk of Cancer or Heart Disease in Postmenopausal Women.” Fred Hutchinson Cancer Research Center. Center News 16 (February 2009).

Key Takeaways

Foods contain nutrients that are essential for our bodies to function. Four of the nutrient classes 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. One measurement of food quality is the amount of essential nutrients a food contains relative to the amount of energy it has (nutrient density).