43 14.4 Metabolism and Nutrition
Metabolism and Nutrition[1]
A balanced diet rich in fruits and vegetables is essential for good health. A range of nutrients is necessary for cells to carry out their daily jobs to build, repair, and maintain the body. Diet, including what and how much is consumed, can have a dramatic impact on health. Unhealthy diet choices can increase risk for cardiovascular disease, cancer, anorexia, diabetes, and other chronic diseases.
Metabolism is the sum of all of the chemical reactions that occur in the body. Metabolism across individuals varies, depending on genetics, age, sex, activity level, nutrient consumption, and lean body mass. Metabolic rate also fluctuates throughout life and can be modified by diet and exercise regimens. Aging decreases the metabolic rate by as much as 5 percent per year. Additionally, because males tend to have more lean muscle mass than females, their basal metabolic rate (metabolic rate at rest) is higher, so males tend to burn more calories than females do.
Despite factors affecting metabolism, all humans have the same overall metabolic processes. Metabolism can be categorized based on reactions that breakdown or build up. Catabolism (also referred to as a catabolic reaction) is the breakdown of large molecules into smaller ones. In digestion, food is broken down to obtain energy. Anabolic reactions, or anabolism uses the energy produced by catabolic reactions to build larger molecules from smaller ones, such as when the body forms proteins by stringing together amino acids. Both sets of reactions are critical to maintaining life.
Nutrients
A nutrient is a substance in foods and beverages that is essential for energy, growth, and the maintenance and repair of tissues. The three basic nutrient classes are water, macronutrients (carbohydrates, lipids, and proteins), and micronutrients (vitamins and minerals). Water and macronutrients are needed in large amounts.
Water
The most critical nutrient is water. Depending on the environmental temperature and one’s state of health, humans can survive for only a few days without water. The body’s chemicals are dissolved and transported in water, and the chemical reactions of life take place in water. Water is the largest component of cells, blood, and the fluid between cells, making up about 70 percent of an adult’s body mass. Water also helps regulate our internal temperature and cushions, protects, and lubricates joints and many other body structures.
Energy Yielding and Body Building Nutrients
The energy-yielding nutrients are primarily carbohydrates and lipids, while proteins mainly supply the amino acids that are the building blocks of the body itself. These nutrients are ingested in foods and beverages made from animal and plant sources, and the digestive system breaks them down into molecules small enough to be absorbed. The breakdown products of carbohydrates and lipids can then be used in the metabolic processes that convert them to ATP.
Review the chemical structure of nutrients and the action of ATP in the “Organic and Inorganic Compounds” section of the “Chemical Components of Living Things” chapter.
Vitamins and Minerals
Micronutrients are nutrients that are needed by the body in small amounts and include vitamins and minerals. While they are needed in smaller amounts than macronutrients, they are absolutely essential for homeostasis. These elements and compounds participate in many essential chemical reactions and processes, such as nerve impulses. Some also contribute to the body’s structure, such as calcium. The body can store some micronutrients in tissues and draw on those reserves if they are not obtained in the diet for a few days or weeks. Other micronutrients, such as vitamin C and most of the B vitamins, are water-soluble and cannot be stored, so these nutrients must be consumed in the diet every day or two.
Vitamins
Vitamins are organic compounds found in foods and are a necessary part of the biochemical reactions in the body. They are involved in a number of processes, including mineral and bone metabolism, cell and tissue growth, and energy metabolism. The B vitamins play the largest role of any vitamins in metabolism. Most vitamins are consumed through food, although some can be formed from substances absorbed during digestion. For example, the body makes vitamin A from the β-carotene in orange vegetables such as carrots and sweet potatoes.
Vitamins are either fat-soluble or water-soluble. Fat-soluble vitamins (vitamins A, D, E, and K) are absorbed into the lymphatic system through the intestinal tract. Vitamin D is also made in the skin through exposure to sunlight. Because they are carried in lipids, fat-soluble vitamins can accumulate in the lipids stored in the body. If excess vitamins accumulate in the body, hypervitaminosis can result.
Water-soluble vitamins (including vitamin C and the eight B vitamins) are absorbed with water in the gastrointestinal tract. These vitamins move easily through bodily fluids that are water based, so they are not stored in the body. Excess water-soluble vitamins are excreted in the urine. Therefore, hypervitaminosis of water-soluble vitamins rarely occurs, except if an excess of vitamin supplements are consumed.
See Table 14.4 for a summary of fat-soluble vitamins and Table 14.4a for a summary of water-soluble vitamins.
Table 14.4 Fat-Soluble Vitamins[2]
Vitamin |
Sources |
Recommended Daily Allowance |
Function |
Problems Associated With Deficiency |
| A
(retinol or β-carotene) |
Yellow and orange fruits and vegetables, dark green leafy vegetables, eggs, milk, liver | 700–900 µg | Eye and bone development, immune function | Night blindness, skin issues, and immune system deficiency |
| D
(cholecalciferol) |
Dairy products, egg yolks; also synthesized in the skin from exposure to sunlight | 5–15 µg | Aids in calcium absorption, promoting bone growth | Rickets, bone pain, muscle weakness, increased risk of death from cardiovascular disease, cognitive impairment, asthma in children, and cancer |
| E
(tocopherols) |
Seeds, nuts, vegetable oils, avocados, wheat germ | 15 mg | Antioxidant | Anemia |
| K
(phytonadione) |
Dark green leafy vegetables, broccoli, Brussels sprouts, cabbage | 90–120 µg | Blood clotting, bone health | Hemorrhagic disease of newborn in infants; uncommon in adults |
Table 14.4a Water-Soluble Vitamins[3]
Vitamin |
Sources |
Recommended Daily Allowance |
Function |
Problems Associated With Deficiency |
| B1
(thiamine) |
Whole grains, enriched bread and cereals, milk, meat | 1.1–1.2 mg | Carbohydrate metabolism | Beriberi, and Wernicke-Korsakoff syndrome |
| B2
(riboflavin) |
Brewer’s yeast, almonds, milk, organ meats, legumes, enriched breads and cereals, broccoli, asparagus | 1.1–1.3 mg | Cellular metabolism, production of red blood cells | Fatigue, slowed growth, digestive problems, light sensitivity, and epithelial problems like cracks in the corners of the mouth |
| B3
(niacin) |
Meat, fish, poultry, enriched breads and cereals, peanuts | 14–16 mg | Cellular metabolism, nerve function, cholesterol production | Cracked, scaly skin and dementia; diarrhea; also known as pellagra |
| B5
(pantothenic acid) |
Meat, poultry, potatoes, oats, enriched breads and cereals, tomatoes | 5 mg | Synthesis of coenzyme A in fatty acid metabolism | Rare: symptoms may include fatigue, insomnia, depression, and irritability |
| B6
(pyridoxine) |
Potatoes, bananas, beans, seeds, nuts, meat, poultry, fish, eggs, dark green leafy vegetables, soy, organ meats | 1.3–1.5 mg | Sodium and potassium balance, red blood cell synthesis, protein metabolism | Confusion, irritability, depression, and mouth and tongue sores |
| B7
(biotin) |
Liver, fruits, meats | 30 µg | Cell growth, metabolism of fatty acids, production of blood cells | Rare in developed countries; symptoms include dermatitis, hair loss, and loss of muscular coordination |
| B9
(folic acid) |
Liver, legumes, dark green leafy vegetables, enriched breads and cereals, citrus fruits | 400 µg | DNA/protein synthesis | Poor growth, gingivitis, appetite loss, shortness of breath, gastrointestinal problems, and mental deficits. Deficiency during pregnancy can cause neural tube defects in the embryo. |
| B12
(cyanocobalamin) |
Fish, meat, poultry, dairy products, eggs | 2.4 µg | Fatty acid oxidation, nerve cell function, red blood cell production | Pernicious anemia, leading to nerve cell damage |
| C
(ascorbic acid) |
Citrus fruits, red berries, peppers, tomatoes, broccoli, dark green leafy vegetables | 75–90 mg | Necessary to produce collagen for formation of connective tissue and teeth, and for wound healing | Dry hair, gingivitis, bleeding gums, dry and scaly skin, slow wound healing, easy bruising, and compromised immunity; can lead to scurvy |
Minerals
Minerals are inorganic compounds that work with other nutrients to ensure the body functions properly. Minerals cannot be produced in the body so they must be consumed through food. The amount of minerals in the body is small—only 4 percent of the total body mass. Minerals that the body requires in moderate quantities include potassium, sodium, calcium, phosphorus, magnesium, and chloride.
The most common minerals in the body are calcium and phosphorus, both of which are stored in the skeleton and necessary for the hardening of bones. Most minerals exist in the body as their ionic form (cation or anion), and these ionic forms are used in physiological processes throughout the body. Sodium and chloride ions act as electrolytes in the blood and extracellular tissues, and iron ions are critical to the formation of hemoglobin. There are additional trace minerals that are still important to the body’s functions, but their required quantities are much lower.
A healthy diet includes most of the minerals the body requires, so supplements and processed foods can add potentially toxic levels of minerals. Like vitamins, minerals can be consumed in toxic quantities, although it is rare. See 14.4b for a summary of major minerals and Table 14.4c for a summary of trace minerals.
Table 14.4b Major Minerals[4]
Mineral |
Sources |
Recommended Daily Allowance |
Function |
Problems Associated With Deficiency |
| Potassium | Meats, some fish, fruits, vegetables, legumes, dairy products | 4,700 mg | Nerve and muscle function; acts as an electrolyte | Hypokalemia: weakness, fatigue, muscle cramping, gastrointestinal problems, and cardiac problems |
| Sodium | Table salt, milk, beets, celery, processed foods | 2,300 mg | Blood pressure, blood volume, and muscle and nerve function | Rare |
| Calcium | Dairy products, dark green leafy vegetables, blackstrap molasses, nuts, brewer’s yeast, some fish | 1,000 mg | Bone structure and health; nerve and muscle functions, especially cardiac function | Slow growth, and weak and brittle bones |
| Phosphorous | Meat, milk | 700 mg | Bone formation, metabolism, ATP production | Rare |
| Magnesium | Whole grains, nuts, leafy green vegetables | 310–420 mg | Enzyme activation, production of energy, regulation of other nutrients | Agitation, anxiety, sleep problems, nausea and vomiting, abnormal heart rhythms, low blood pressure, and muscular problems |
| Chloride | Most foods, salt, vegetables, especially seaweed, tomatoes, lettuce, celery, olives | 2,300 mg | Balance of body fluids, digestion | Loss of appetite and muscle cramps |
Table 14.4c Trace Minerals[5]
Mineral |
Sources |
Recommended Daily Allowance |
Function |
Problems Associated with Deficiency |
| Iron | Meat, poultry, fish, shellfish, legumes, nuts, seeds, whole grains, dark leafy green vegetables | 8–18 mg | Transport of oxygen in blood, production of ATP | Anemia, weakness, and fatigue |
| Zinc | Meat, fish, poultry, cheese, shellfish | 8–11 mg | Immunity, reproduction, growth, blood clotting, insulin and thyroid function | Loss of appetite, poor growth, weight loss, skin problems, hair loss, vision problems, and lack of taste or smell |
| Copper | Seafood, organ meats, nuts, legumes, chocolate, enriched breads and cereals, some fruits and vegetables | 900 µg | Red blood cell production, nerve and immune system function, collagen formation, acts as an antioxidant | Anemia, low body temperature, bone fractures, low white blood cell concentration, irregular heartbeat, and thyroid problems |
| Iodine | Fish, shellfish, garlic, lima beans, sesame seeds, soybeans, dark leafy green vegetables | 150 µg | Thyroid function | Hypothyroidism: fatigue, weight gain, dry skin, and temperature sensitivity |
| Sulfur | Eggs, meat, poultry, fish, legumes | None | Component of some amino acids | Protein deficiency |
| Fluoride | Fluoridated water | 3–4 mg | Maintenance of bone and tooth structure | Increased cavities and weak bones and teeth |
| Manganese | Nuts, seeds, whole grains, legumes | 1.8–2.3 mg | Formation of connective tissue and bones, blood clotting, sex hormone development, metabolism, brain and nerve function | Infertility, bone malformation, weakness, and seizures |
| Cobalt | Fish, nuts, leafy green vegetables, whole grains | None | Component of B12 | None |
| Selenium | Brewer’s yeast, wheat germ, liver, butter, fish, shellfish, whole grains | 55 µg | Antioxidant, thyroid function, immune system function | Muscle pain |
| Chromium | Whole grains, lean meats, cheese, black pepper, thyme, brewer’s yeast | 25–35 µg | Insulin function | High blood sugar, triglyceride, and cholesterol levels |
| Molybdenum | Legumes, whole grains, nuts | 45 µg | Cofactor for enzymes | Rare |
- Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., Kruse, D. H., Korol, O., Johnson, J. E., Womble, M., & DeSaix, P. (2022). Anatomy and physiology 2e. OpenStax. https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction ↵
- Ernstmeyer, K., & Christman, E. (Eds.). (2024). Medical terminology 2e. Open RN | WisTech Open. https://wtcs.pressbooks.pub/medterm/ ↵
- Ernstmeyer, K., & Christman, E. (Eds.). (2024). Medical terminology 2e. Open RN | WisTech Open. https://wtcs.pressbooks.pub/medterm/ ↵
- Ernstmeyer, K., & Christman, E. (Eds.). (2024). Medical terminology 2e. Open RN | WisTech Open. https://wtcs.pressbooks.pub/medterm/ ↵
- Ernstmeyer, K., & Christman, E. (Eds.). (2024). Medical terminology 2e. Open RN | WisTech Open. https://wtcs.pressbooks.pub/medterm/ ↵
