Nutrients are the nutritious components in foods that an organism utilizes to survive and grow. Macro-nutrients provide the bulk energy for an organism’s metabolic system to function, while micro-nutrients provide the necessary co-factors for metabolism to be carried out. Both types of nutrients can be acquired from the environment. They are used to build and repair tissues, regulate body processes, and are converted to and used for energy. Methods for nutrient intake are different for plants and animals. Plants take in nutrients directly from the soil through their roots and from the atmosphere through their leaves. Animals and protists have specialized digestive systems that work to break down macro-nutrients for energy and utilize micro nutrients to carry out both metabolism and anabolism or constructive synthesis in the body.
Organic nutrients include carbohydrates, fats, proteins (or their building blocks, amino acids), and vitamins. Inorganic chemical compounds such as dietary minerals, water, and oxygen may also be considered nutrients. A nutrient is said to be “essential” if it must be obtained from an external source, either because the organism cannot synthesize it or produces insufficient quantities. Nutrients needed in very small amounts are micro-nutrients and those that are needed in larger quantities are called macro-nutrients. The effects of nutrients are dose-dependent and shortages are called deficiencies.
TYPES OF NUTRIENTS
Macro-nutrients are defined in several different ways.
- The chemical elements humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur, or CHNOPS.
- The classes of chemical compounds humans consume in the largest quantities and which provide bulk energy are carbohydrates, proteins, and fats. Water and atmospheric oxygen also must be consumed in large quantities, but are not always considered “food” or “nutrients”.
- Calcium, salt (sodium and chloride), magnesium, and potassium (along with phosphorus and sulfur) are sometimes added to the list of macro-nutrients because they are required in large quantities compared to other vitamins and minerals. They are sometimes referred to as the macro-minerals.
Substances that provide energy
- Carbohydrates are compounds made up of types of sugars. Carbohydrates are classified by their number of sugar units: monosaccharides (such as glucose and fructose), disaccharides (such as sucrose and lactose), oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose).
- Proteins are organic compounds that consist of the amino acids joined by peptide bonds. The body cannot manufacture some of the amino acids (termed essential amino acids); the diet must supply them. Proteins, in nutrition, are broken down through digestion by proteases back into free amino acids.
- Fats consist of a glycerin molecule with three fatty acids attached. Fatty acids are unbranched hydrocarbon chains, connected by single bonds alone (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are needed to keep cellmembranes functioning properly, to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids (termed essential fatty acids) and the diet must supply them.
Although alcohol provides energy, and can thus be compared to macro-nutrients, it is not a substance that is essential for normal function. The acetic acid in vinegar also provides a similar amount of energy per gram, but again, it is not a nutrient because it is not essential for normal function.
Fat has an energy content of 9 kcal/g (~37.7 kJ/g); proteins and carbohydrates 4 kcal/g (~16.7 kJ/g). Ethanol (grain alcohol) has an energy content of 7 kcal/g (~29.3 kJ/g).
Substances that support metabolism
- Dietary minerals are generally trace elements, salts, or ions such as copper and iron. Some of these minerals are essential to human metabolism.
- Vitamins are organic compounds essential to the body. They usually act as coenzymes or cofactors for various proteins in the body.
- Water is an essential nutrient and is the solvent in which all the chemical reactions of life take place.
Plants absorb nutrients from the soil or the atmosphere, or from water (mainly aquatic plants). An exception are the carnivorous plants, which externally digest nutrients from animals before ingesting them.
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The chemical elements consumed in the greatest quantities by plants are carbon, hydrogen, and oxygen. These are present in the environment in the form of water and carbon dioxide; energy is provided by sunlight. Nitrogen, phosphorus, and sulfur are also needed in relatively large quantities. Together, the “Big Six” are the elemental macro-nutrients for all organisms, often represented by the acronym CHNOPS. Usually they are sourced from inorganic (e.g. carbon dioxide, water, nitrate, phosphate, sulfate) or organic (e.g. carbohydrates, lipids, proteins) compounds, although elemental diatomic molecules of nitrogen and (especially) oxygen are often used.
Other chemical elements are also necessary to carry out various life processes and build structures;
Some of these are considered macro-nutrients in certain organisms. The mnemonic C. HOPKN’S CaFe Mg (to be used as C. Hopkins coffee mug) is used by some students to remember the list as: carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, and magnesium. Silicon, chloride, sodium, copper, zinc, and molybdenum are sometimes also included, but are in other cases considered micro-nutrients.
Essential and non-essential nutrients
Nutrients are frequently categorized as essential or nonessential. Essential nutrients are unable to be synthesized internally (either at all, or in sufficient quantities), and so must be consumed by an organism from its environment. Nonessential nutrients are those nutrients that can be made by the body, they may often also be absorbed from consumed food. The majority of animals ultimately derive their essential nutrients from plants, though some animals may consume mineral-based soils to supplement their diet.
For humans, these include essential fatty acids, essential amino acids, vitamins, and certain dietary minerals. Oxygen and water are also essential for human survival, but are generally not considered “food” when consumed in isolation.
Humans can derive energy from a wide variety of fats, carbohydrates, proteins, and ethanol, and can synthesize other needed amino acids from the essential nutrients.
Non-essential substances within foods can still have a significant impact on health, whether beneficial or toxic. For example, most dietary fiber is not absorbed by the human digestive tract, but is important in digestion and absorption of otherwise harmful substances. Interest has recently increased in phytochemicals, which include many non-essential substances which may have health benefits.
Deficiencies and toxicity
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes including inadequacy in nutrient intake called dietary deficiency, or conditions that interfere with the utilization of a nutrient within an organism. Some of the conditions that can interfere with nutrient utilization include problems with nutrient absorption, substances that cause a greater than normal need for a nutrient, conditions that cause nutrient destruction, and conditions that cause greater nutrient excretion.
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Nutrient toxicity occurs when an excess of a nutrient does harm to an organism.
In plants five types of deficiency or toxicity symptoms are common:
- Chlorosis – which is the yellowing of plant tissue caused by a shortage of chlorophyll synthesis.
- Necrosis – which is the death of tissue.
- Accumulation of anthocyanin – which produces a purple or reddish colorization of foliage and/or stems.
- Lack of new growth.
- Stunting or reduced growth – where new growth is stunted or reduced.classify*
Oversupply of plant nutrients in the environment can cause excessive plant and algae growth. Eutrophication, as this process is called, may cause imbalances in population numbers and other nutrients that can be harmful to certain species. For example, an algal bloom can deplete the oxygen available for fish to breathe. Causes include water pollution from sewage or runoff from farms (carrying excess agricultural fertilizer). Nitrogen and phosphorus are most commonly the limiting factor in growth, and thus the most likely to trigger eutrophication when introduced artificially.
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