Nutrition

For other uses, see Nutrition (disambiguation).

Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It includes ingestion, absorption, assimilation, biosynthesis, catabolism and excretion. The science that studies the physiological process of nutrition is called nutritional science (also nutrition science).

Nutritional groups

Main article: Primary nutritional groups

Organisms can be classified by how they obtain carbon and energy. Heterotrophs are organisms that obtain nutrients by consuming the carbon of other organisms, while autotrophs are organisms that produce their own nutrients from the carbon of inorganic substances like carbon dioxide. Mixotrophs are organisms that can be heterotrophs and autotrophs, including some plankton and carnivorous plants. Phototrophs obtain energy from light, while chemotrophs obtain energy by consuming chemical energy from matter. Organotrophs consume other organisms to obtain electrons, while lithotrophs obtain electrons from inorganic substances, such as water, hydrogen sulfide, dihydrogen, iron(II), sulfur, or ammonium.

Nutrients

Main article: Nutrient

Nutrients are substances used by an organism to survive, grow, and reproduce. The seven major classes of relevant nutrients for animals (including humans) are carbohydrates, dietary fiber, fats, proteins, minerals, vitamins, and water. Nutrients can be grouped as either macronutrients (carbohydrates, dietary fiber, fats, proteins, and water needed in gram quantities) or micronutrients (vitamins and minerals needed in milligram or microgram quantities).

Diet

Main article: Diet (nutrition)

In nutrition, the diet of an organism is the sum of foods it eats, which is largely determined by the availability and palatability of foods.

Human nutrition

Main article: Human nutrition

Human nutrition deals with the provision of essential nutrients from food that are necessary to support human life and good health. In humans, poor nutrition can cause deficiency-related diseases such as blindness, anemia, scurvy, preterm birth, stillbirth and cretinism, or nutrient excess health-threatening conditions such as obesity and metabolic syndrome; and such common chronic systemic diseases as cardiovascular disease, diabetes, and osteoporosis. Undernutrition can lead to wasting in acute cases, and stunting of marasmus in chronic cases of malnutrition.

Animal nutrition

Main article: Animal nutrition

Animals are heterotrophs that consume other organisms to obtain nutrients. Herbivores are animals that eat plants, carnivores are animals that eat other animals, and omnivores are animals that eat both plants and other animals. Many herbivores rely on bacterial fermentation to create digestible nutrients from indigestible plant cellulose, while obligate carnivores must eat animal meats to obtain certain vitamins or nutrients their bodies cannot otherwise synthesize. Animals generally have a higher requirement of energy in comparison to plants.

In addition to water, animals also require macronutrients and micronutrients. Macronutrients are the primary substances used by the bodies of animals. The macronutrients are carbohydrates, amino acids, and fatty acids. Micronutrients are substances required by animals in trace amounts. Organic micronutrients are classified as vitamins, and inorganic micronutrients are classified as minerals. Carbohydrates are digested to produce glucose and short-chain fatty acids, and they are the most abundant nutrients for herbivorous land animals. Fats and fatty acids are obtained by animals through the digestion of lipids. An animal's body will reduce the amount of fatty acids it produces as dietary fat intake increases, while it increases the amount of fatty acids it produces as carbohydrate intake increases. Amino acids are obtained by animals through the digestion of protein. They contain nitrogen, sulfur, and hydrocarbon skeletons that cannot be substituted by other nutrients.

Plant nutrition

Main article: Plant nutrition

Most plants obtain nutrients through inorganic substances absorbed from the soil. The primary nutrients that make up organic material in a plant and allow enzymic processes are carbon, hydrogen, oxygen, nitrogen, and silicon, and these nutrients can also be absorbed from the atmosphere. As these nutrients do not provide the plant with energy, plants must obtain energy by other means. Green plants absorb energy from sunlight with chloroplasts and convert it to usable energy through photosynthesis.

Plants uptake essential elements from the soil through their roots and from the air (consisting of mainly nitrogen and oxygen) through their leaves. Nutrient uptake in the soil is achieved by cation exchange, wherein root hairs pump hydrogen ions (H⁺) into the soil through proton pumps. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, stomata open to take in carbon dioxide and expel oxygen. Although nitrogen is plentiful in the Earth's atmosphere, very few plants can use this directly. Most plants, therefore, require nitrogen compounds to be present in the soil in which they grow. This is made possible by the fact that largely inert atmospheric nitrogen is changed in a nitrogen fixation process to biologically usable forms in the soil by bacteria.

Fungus nutrition

See also: Fungiculture

Fungi are chemoheterotrophs that consume external matter for energy. Most fungi absorb matter through the root-like mycelium, which grows through the organism's source of nutrients and can extend indefinitely. The fungus excretes extracellular enzymes to break down surrounding matter and then absorbs the nutrients through the cell wall. Fungi can be parasitic, saprophytic, or symbiotic. Parasitic fungi attach and feed on living hosts, such as animals, plants, or other fungi. Saprophytic fungi feed on dead and decomposing organisms. Symbiotic fungi grow around other organisms and exchange nutrients with them.

See also

• Auxology
• Exercise
• Nutrition psychology
• Physical fitness

Bibliography

• Mengel, Konrad; Kirkby, Ernest A.; Kosegarten, Harald; Appel, Thomas, eds. (2001). Principles of Plant Nutrition (5th ed.). Springer. doi:10.1007/978-94-010-1009-2. ISBN 9789401010092.
• Wu, Guoyao (2017). Principles of Animal Nutrition. CRC Press. ISBN 9781351646376.

Further reading

• Carpenter, Kenneth J. (1994). Protein and Energy: A Study of Changing Ideas in Nutrition. Cambridge University Press. ISBN 978-0-521-45209-0.
• Curley, S., and Mark (1990). The Natural Guide to Good Health, Lafayette, Louisiana, Supreme Publishing
• Galdston, I. (1960). Human Nutrition Historic and Scientific. New York: International Universities Press.
• Gratzer, Walter (2006) [2005]. Terrors of the Table: The Curious History of Nutrition. Oxford University Press. ISBN 978-0-19-920563-9.
• Mahan, L.K.; Escott-Stump, S., eds. (2000). Krause's Food, Nutrition, and Diet Therapy (10th ed.). Philadelphia: W.B. Saunders Harcourt Brace. ISBN 978-0-7216-7904-4.
• Thiollet, J.-P. (2001). Vitamines & minéraux. Paris: Anagramme.
• Walter C. Willett; Meir J. Stampfer (January 2003). "Rebuilding the Food Pyramid". Scientific American. 288 (1): 64–71. Bibcode:2003SciAm.288a..64W. doi:10.1038/scientificamerican0103-64. PMID 12506426.

External links

• Diet, Nutrition and the prevention of chronic diseases by a Joint WHO/FAO Expert consultation (2003)
• UN Standing Committee on Nutrition – In English, French and Portuguese