1.3 Nutrients and Other Compounds Found in Food

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. 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).

Figure 1.3 Essential Nutrients

Energy Nutrients (macronutrients)

Nutrients that are needed in large amounts and provide energy are called macronutrients. There are three classes of macronutrients: carbohydrates, lipids, and proteins. These can be metabolically processed into cellular energy. The energy from 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. We will learn more about how this happens in chapter 9. The unit of measurement for food energy is the calorie. On nutrition food labels the amount given for “calories” is actually equivalent to each calorie multiplied by one thousand. A kilocalorie (kcal) or one thousand calories, denoted with a small “c” is synonymous with the “Calorie” (with a capital “C”) on nutrition food labels.

Carbohydrate and protein both provide 4 Calories or kcals per gram. Carbohydrate is your body’s preferred source of energy and the primary source of fuel for your brain. Protein can be used to provide energy when carbohydrate stores are low but your body prefers to use protein to build and maintain tissues, including muscle tissue. Lipids (fats) are more energy dense and provide 9 Calories or kcals per gram making lipids your body’s primary form of stored energy. In addition to the three macronutrients, the non-nutrient alcohol contains 7 Calories or kcals per gram. Alcohol is the only substance that provides energy and is not a nutrient. Alcohol is referred to as empty calories because it contains 7 kcals/gram but does not provide any nutritional value.

Table 1.1 Energy Content of the Energy Nutrients and Alcohol

Micronutrients

Micronutrients are nutrients required by the body in lesser amounts (mg or mcg) and do not provide calories, 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. Even though they do not provide energy (calories), micronutrients assist in chemical reactions that produce energy. You will learn about some of these reactions in chapter 8.

The thirteen vitamins are categorized as either water-soluble or fat-soluble. The water-soluble vitamins are vitamin C and 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, synthesizing bone tissue, and 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 found out 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).

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 amounts of a few milligrams or less. Major minerals, such as calcium, magnesium, potassium, sodium, and phosphorus, are required in doses of 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 in the body that can cause health problems such as cancer.

Water

The sixth essential nutrient is water. Water is neither a macronutrient or a micronutrient because it is needed in large quantities but does not provide energy in the form of calories. Approximately 60% of your body is composed of water, making water very essential. 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. Dehydration can affect metabolism and exercise performance so it is crucial that individuals consume adequate amounts of water from foods and beverages. The amount of water an individual requires can vary greatly and depends on body size, environment (hot or humid environments make you sweat more), and activity patterns because exercise and other physical activities increase sweat rate. The simplest way to assess hydration status is to monitor urine color and frequency. If your urine is straw colored and you are urinating frequently, you are likely consuming enough water.

Phytochemicals

In addition to nutrients, food also provides beneficial substances called phytochemicals that protect our health in other ways. The word “phyto” is the Latin root word for plant, so phytochemicals are “plant” chemicals. Phytochemicals are chemicals found naturally occurring in all plant foods that give plants their different colors, smells, and flavors. Different plants contain different phytochemicals so it is recommended to eat a variety of colorful plants to obtain the most benefit from phytochemicals. Phytochemicals are not considered essential nutrients because they are not linked with a specific deficiency disease. However, they help reduce our risk of chronic diseases such as cancer and heart disease. Many phytochemicals have antioxidant properties and protect cells from being damaged or destroyed by exposure to certain environmental and internal substances. We can say that phytochemicals may help prevent certain chronic diseases, but a lack of phytochemicals will not cause a specific deficiency disease.