As nutrients refers to various organic and inorganic substances by living organisms added to the life support and metabolism are processed. The diversity and the different needs of living things can still be summarized in essential nutrient groups. Above all, the type, origin, use and the quantitative requirement of the nutrients serve as the basis for categorization.
According to another definition, only high-energy substances are referred to as nutrients that are broken down in the organism into substances with less energy and mainly serve to supply the body with energy. Minerals and vitamins then do not count as nutrients.
In soil science and in the agricultural science discipline of plant nutrition (phytotrophology), plant nutrients are designated according to the chemical elements required . Carbon , oxygen and hydrogen are available in practically unlimited quantities in the form of carbon dioxide and water , all other elements are mainly absorbed in the form of dissolved inorganic compounds and ions as minerals . These are classified according to the dry matter content of the plants or the daily requirement: macro elements or main nutritional elements and micro elements or trace elements .
Many nutrients can be produced from others by consuming energy, others have to be taken in with food, these are called essential nutrients .
Carbohydrates are mainly used to provide the animal organism with quick energy . They are not considered essential and can be synthesized in gluconeogenesis . In the short term, glucose is stored as glycogen in the liver and muscle tissue . When the supply of carbohydrates to tissues is greater than their consumption, the excess is converted into fat and stored . Energy is normally released in the non-oxidative glycolysis and in the oxidative citrate cycle . The energy density of carbohydrates is around 17.2 kJ / g (4.1 kcal / g).
Non-digestible carbohydrates play an important role as fiber .
Many plants are specifically grown as a source of carbohydrates . The most important carbohydrates in the diet are:
- Starch from all types of grain and grain products ( bread , pasta ), potatoes , beans
- Cellulose from grasses , among other things , can be used as animal feed by ruminants due to bacterial degradation in the rumen ; for humans it is indigestible ( fiber )
- Sucrose from sugar cane and sugar beet
- Fructose made from fruit and honey
- Dextrose from honey and as a component of other sugars
- Milk sugar from milk and milk products
Liquid fatty oils and solid fats, with a calorific value of approx. 39 kJ / g (9.3 kcal / g) that is about twice as high as that of carbohydrates and proteins, are a good source of energy and, together with glycogen, an important energy store in the body. To generate energy, a fat molecule is split into glycerine and three fatty acids , the latter are further broken down via β-oxidation and inserted into the citric acid cycle . Doubly unsaturated fatty acids cannot be produced by the body and must be taken in with food. The best known examples are the omega-3 and omega-6 fatty acids . Numerous crops and animals are important sources of edible fats .
- Oil from whales and seals
- Tallow from cattle and sheep
- Lard from pigs and geese
- Butter and clarified butter
- Fatty fish such as herring , sardine and anchovy , salmon , mackerel , or eel
Proteins (proteins) are converted into the body's own substances , especially in the building metabolism. In addition to structural proteins as in muscles , enzymes should also be mentioned here. For this purpose, the proteins are first split into the basic building blocks, the amino acids , and then put together to form new proteins. The effectiveness of this conversion is described with the biological value . Many amino acids can be synthesized from others ; others must be taken in with food as essential amino acids . Proteins are also used to generate energy and fed into the citric acid cycle; like carbohydrates, one gram also provides around 17.2 kJ (4.1 kcal) of energy.
- Dairy products
- Legumes such as lentils , beans , peas or soybeans
- Grains (wheat, rye, oats, rice, millet), pseudograins (buckwheat, quinoa, amaranth)
- Potatoes (only 2%, but a lot of essential amino acids)
- Algae, sprouts
The minerals are inorganic substances that are found in both animal and vegetable foods. Like vitamins, they are essential substances that must be ingested with food, but do not provide the body with energy.
Vitamins are organic compounds that the organism does not need as a source of energy but for other vital functions, but which the metabolism cannot synthesize as required. Vitamins have to be taken in with food, they are essential substances. Plants do not need vitamins, they can synthesize all the organic substances they need by themselves.
- Lincoln Taiz, Eduardo Zeiger: Physiology of Plants. 1st edition. Spectrum Academic Publishing House, 2000, ISBN 3-8274-0537-8 .
- Roger Eckert: Animal Physiology. 4th revised edition. Georg Thieme Verlag, 2002, ISBN 3-13-664004-7 .
- Thews / Mutschler / Vaupel: anatomy, physiology and pathophysiology of humans. Wissenschaftliche Verlagsgesellschaft, Stuttgart 1999, p. 313.