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1.4: Overview of Nutrients and Calories

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  • 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 is in Food?

    Your "diet" is defined as the foods you choose to eat. The diet of most people contains a variety of foods: grains, nuts, fruits, vegetables and more. The foods we eat contain nutrients. Nutrients are substances required by the body to perform its basic functions. Nutrients must be obtained from diet, since the human body does not synthesize them, or does not synthesize them in large enough amounts for human health. Nutrients are used for many body functions such as growing, moving your muscles, repairing tissues and much more.  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. 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.


    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).


    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.


    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.


    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 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.


    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
    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
    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


    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
    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
    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.

    Food Energy

    Though this is only Chapter 1, you have already seen the words "calories" and "energy" used several times. In everyday life you have probably heard people talk about how many calories they burned on the treadmill or how many calories are listed on a bag of chips. Calories are a measure of food energy. It takes quite a lot of calories (energy) to keep us alive. Even if a person is in a coma, they still burn calories in order for their heart to beat, their blood to circulate, their lungs to breathe, etc. We burn even more calories when we exercise. The carbohydrates, fats and proteins we eat and drink provide calories for us. Sometimes people refer to these essential nutrients as "energy yielding". As you read above, carbohydrates provide 4 calories for every gram we consume; proteins provide 4 calories for every gram we consume; and fats provide 9 calories for every gram we consume. Another source of calories is alcohol. Alcohol is not considered to be a nutrient (because it's not required by the body to perform its basic functions), but it does provide 7 calories of energy for every gram we consume. Vitamins, minerals and water do not provide any calories, but they are still essential nutrients.

    Technically, food energy is measured in kilocalories. A kilocalorie is the amount of heat generated by a particular macronutrient that raises the temperature of 1 kilogram of water 1 degree Celsius. To measure the number of kilocalories in a particular food substance, a certain amount of food is burned in a device called a calorimeter. As the food burns, heat is created. The heat dissipates to the surrounding water while a thermometer detects the change in temperature of the water. A kilocalorie of energy performs one thousand times more work than a calorie. In science, a kilocalorie is often written as "kcal" or "Calorie" (with a capital "C"). So, 1 kilocalorie = 1 kcal = 1 Calorie = 1,000 calories. Although kilocalories, kcals, or Calories (with a capital "C") are technically the appropriate terms, most people refer to the amount of energy in food as a calorie (with a lower case "c"), so this text will use calories (with a lower case "c") for the sake of simplicity.  On food labels, "calorie" is used when referring to kilocalories.

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

    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.


    Learning Check \(\PageIndex{1}\)