1.2 What Are Nutrients?

CarbohydratesOrganic molecules composed of carbon, hydrogen, and oxygen. There are two basic forms: simple sugars and complex sugars. are organic molecules composed of carbon, hydrogen, and oxygen that are found in food and living tissues. They typically contain hydrogen and oxygen in a 2:1 ratio, the same as in water (which is why they are called carbohydrates). The major food sources of carbohydrates are grains, milk, fruits, and starchy vegetables like potatoes. Nonstarchy vegetables also contain carbohydrates, but in lesser quantities. Carbohydrates can be categorized as sugars, starches, and fiber.

Sugars 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.

Slow-releasing carbohydrates are long chains of simple sugars that can be branched or unbranched. During digestion, the body breaks down all slow-releasing carbohydrates to 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.

Fiber is also a carbohydrate, but it cannot be broken down in the human body and instead 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.

LipidsA family of organic compounds composed of carbon, hydrogen, and oxygen. They are insoluble in water. The three main types of lipids are triglycerides, phospholipids, and sterols. are also a family of molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. 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 lipid versus four kilocalories per gram of carbohydrate). In addition to energy storage, lipids serve as an important component of cell membranes, surround and protect organs, aid in temperature regulation, and regulate many other functions in the body.

ProteinsMacromolecules composed of chains of organic monomeric subunits, called amino acids. Amino acids are simple monomers composed of carbon, oxygen, hydrogen, and nitrogen. 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, eggs, 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 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 most of the chemical reactions that take place in the body. Scientists estimate that more than one-hundred thousand different proteins exist within the human body.

There is one other nutrient that we must have in large quantities: water. Water does not contain carbon, but rather is composed of two hydrogens and one oxygen per molecule of water. Approximately 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. 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 one’s water input and output is extremely important, a topic we will explore in detail in Chapter 7 “Nutrients Important to Fluid and Electrolyte Balance”.

Vitamins are organic compounds that are required in small amounts for the body’s functioning and that cannot be produced by the body. 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, 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.

Vitamin deficiencies can cause severe health problems. For example, a deficiency in niacin causes a disease called pellagra A disease caused by niacin deficiency. , 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 psychiatric asylums awaiting death (refer to “Pellagra”). Other vitamins were also found to prevent certain disorders and diseases, such as scurvy (vitamin C), night blindness (vitamin A), and rickets (vitamin D).

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, 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.