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1.1: Introduction to Nutrition

  • Page ID
    6758
  • Chapter Skills to Develop

    • Describe basic concepts in nutrition
    • Describe factors that affect your nutritional needs
    • Describe the importance of research and scientific methods to understanding nutrition

    ʻO ke kahua ma mua, ma hope ke kūkulu

    The foundation comes first, then the building

    Fig 1.1.1.jpg

    Figure \(\PageIndex{1}\): Image by Jim Hollyer / CC BY 4.0.

    What are Nutrients?

    Nutrients are substances required by the body to perform its basic functions. Most 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. Nutritious foods provide nutrients for the body.  Foods may also contain a variety of non-nutrients.  Some non-nutrients such as as antioxidants (found in many plant foods) are beneficial to the body, whereas others such as natural toxins (common in some plant foods) or additives (like certain dyes and preservatives found in processed foods) are potentially harmful.

    Macronutrients

    Nutrients that are needed in large amounts are called macronutrients. There are three classes of macronutrients: carbohydrates, lipids, and proteins.  Macronutrients are carbon-based compounds that can be metabolically processed into cellular energy through changes in their chemical bonds. The chemical energy is converted into cellular energy known as ATP, that is utilized by the body to perform work and conduct basic functions.

    The amount of energy a person consumes daily comes primarily from the 3 macronutrients.  Food energy is measured in kilocalories.  For ease of use, food labels state the amount of energy in food in “calories,” meaning that each calorie is actually multiplied by one thousand to equal a kilocalorie.  (Note: Using scientific terminology, “Calorie” (with a capital “C”) is equivalent to a kilocalorie. Therefore: 1 kilocalorie = 1 Calorie - 1000 calories

    Water is also a macronutrient in the sense that the body needs it in large amounts, but unlike the other macronutrients, it does not contain carbon or yield energy.

    Note: Consuming alcohol also contributes energy (calories) to the diet at 7 kilocalories/gram, so it must be counted in daily energy consumption.  However, alcohol is not considered a "nutrient" because it does not contribute to essential body functions and actually contains substances that must broken down and excreted from the body to prevent toxic effects.

    Fig 1.1.2.jpg

    Figure \(\PageIndex{2}\): The Macronutrients: Carbohydrates, Lipids, Protein, and Water.

    Carbohydrates

    Carbohydrates are molecules composed of carbon, hydrogen, and oxygen that provide energy to the body. The major food sources of carbohydrates are milk, grains, 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 simple sugars) and complex carbohydrates.

    Simple carbohydrates consist of one or two basic sugar units linked together.  Their scientific names are "monosaccharides" (1 sugar unit) and disaccharides (2 sugar units). They are broken down and absorbed very quickly in the digestive tract and provide a fast burst of energy to the body. Examples of simple sugars include the disaccharide sucrose, the type of sugar you would have in a bowl on the breakfast table, and the monosaccharide glucose, the most common type of fuel for most organisms including humans.  Glucose is the primary sugar that circulates in blood to provide energy to cells. The terms "blood sugar" and "blood glucose" can be substituted for each other.  

    Complex carbohydrates are long chains of sugars units that can link in a straight chair or a branched chain. During digestion, the body breaks down digestible complex carbohydrates into simple sugars, mostly glucose. Glucose is then absorbed into the bloodstream and 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 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 4 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 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 triglycerides (triacylglycerols), phospholipids, and sterols. The main job of triacylglycerols is to provide or store energy.  Lipids provide more energy per gram than carbohydrates (9 kilocalories per gram of lipids versus 4 kilocalories per gram of carbohydrates). In addition to energy storage, lipids serve as a major component of cell membranes, surround and protect organs (in fat-storing tissues), provide insulation to aid in temperature regulation.  Phospholipds and sterols have a somewhat different chemical structure and are used to regulate many other functions in the body.

    Proteins

    Proteins are macromolecules composed of chains of basic subunits called amino acids. Amino acids are 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. The word protein comes from a Greek word meaning “of primary importance,” which is an apt description of these macronutrients; they are also known colloquially as the “workhorses” of life. Proteins provide the basic structure to bones, muscles and skin, enzymes and hormones and play a role in conducting most of the chemical reactions that take place in the body. Scientists estimate that greater than one-hundred thousand 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.  Because amino acids contain carbon, they can be used by the body for energy and supply 4 kilocalories of energy per gram; however providing energy is not protein’s most important function.

    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. More than 60 percent of your total body weight is water. Without water, nothing could be transported in or out of the body, chemical reactions would not occur, organs would not be cushioned, and body temperature would widely fluctuate. On average, an adult consumes just over two liters of water per day from both eating foods and drinking liquids. Since water is so critical for life’s basic processes, total water intake and output is supremely important.  This topic will be explored in detail in Chapter 4.

     

    Table \(\PageIndex{1}\): Functions of Nutrients.
    Nutrients Primary Function
    Carbohydrates Provide a ready source of energy for the body (4 kilocalories/gram) and structural constituents for the formation of cells.
    Fat Provides stored energy for the body (9 kilocalories/gram), functions as structural components of cells and also as signaling molecules for proper cellular communication. It provides insulation to vital organs and works to maintain body temperature.
    Protein Necessary for tissue and organ formation, cellular repair and hormone and enzyme production. Provide energy, but not a primary function (4 kilocalories/gram)
    Water Transports essential nutrients to all body parts, transports waste products for disposal and aids with body temperature regulation
    Minerals Regulate body processes, are necessary for proper cellular function, and comprise body tissue.
    Vitamins Regulate body processes and promote normal body-system functions.

    Micronutrients

    Micronutrients are also essential for carrying out bodily functions, but they are required by the body in lesser amounts. Micronutrients include all the essential minerals and vitamins. There are sixteen essential minerals and thirteen essential vitamins (See Table \(\PageIndex{1}\) and Table \(\PageIndex{2}\) for a complete list and their major functions).

    In contrast to carbohydrates, lipids, and proteins, micronutrients are not sources of energy (calories) for the body. Instead they play a role as cofactors or components of enzymes (i.e., coenzymes) that facilitate chemical reactions in the body.  They are involved in all aspects of body functions from producing energy, to digesting nutrients, to building macromolecules. Micronutrients play many essential roles in the body.

    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. Macrominerals, 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.

    Table \(\PageIndex{1}\): 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

    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 assisting in energy production, making red blood cells, synthesizing bone tissue, and supporting 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).

    Table \(\PageIndex{2}\): Vitamins and Their Major Functions.
    Vitamins Major Functions
    Water-soluble
    Thiamin (B1) Coenzyme, energy metabolism assistance
    Riboflavin (B2 ) Coenzyme, energy metabolism assistance
    Niacin (B3) Coenzyme, energy metabolism assistance
    Pantothenic acid (B5) Coenzyme, energy metabolism assistance
    Pyridoxine (B6) Coenzyme, amino acid synthesis assistance
    Biotin (B7) Coenzyme, amino acid and fatty acid metabolism
    Folate (B9) Coenzyme, essential for growth
    Cobalamin (B12) Coenzyme, red blood cell synthesis
    C (ascorbic acid) 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

     

     

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