Nutrition

Nutrition is how living things use food and water to stay alive, involving biochemical and physiological processes. The field that studies this as a hard science—nutritional science—mostly focuses on humans, but what any organism needs and how it gets those needs depends on the organism itself. Organisms take in nutrients (split into macronutrients and micronutrients) that can be turned into energy and building blocks; getting too much or too little of an essential nutrient leads to malnutrition.

What an organism requires and how it obtains nutrients varies by type. Some consume organic matter, some consume inorganic matter, some absorb light, and others combine these methods. Certain organisms can make nutrients internally from basic elements, while others must eat other organisms to get pre-existing nutrients. All life needs carbon, energy, and water, plus various other molecules. Animals need complex nutrients like carbohydrates, lipids, and proteins, which they get by eating other organisms. Humans replaced foraging with agriculture and cooking to improve their nutrition. Plants take in nutrients from soil and the atmosphere. Fungi break down materials around them and absorb nutrients through their mycelium.

**History** The chemical revolution in the late 1700s kicked off scientific analysis of food and nutrients. During the 1700s and 1800s, chemists tested different elements and food sources to build theories of nutrition. Modern nutrition science took off in the 1910s as individual micronutrients were identified. Thiamine became the first vitamin chemically identified, in 1926, and vitamin C was recognized as a defense against scurvy in 1932. The decades that followed focused on vitamins’ roles in nutrition. The first recommended dietary allowances for humans came about due to fears of deficiency diseases during the Great Depression and World War II. Because nutrition matters so much for human health, the field has heavily emphasized human nutrition and agriculture, with ecology as a secondary concern.

**Nutrients** Nutrients are substances that supply energy and physical components, letting an organism survive, grow, and reproduce. They can be basic elements or complex macromolecules. About 30 elements appear in organic matter, with nitrogen, carbon, and phosphorus being the most important. Macronutrients are the main substances an organism needs; micronutrients are needed only in trace amounts. Organic micronutrients are called vitamins, and inorganic ones are called minerals. Getting too many macronutrients is a major cause of obesity and raises the risk of several non-communicable diseases, such as type 2 diabetes, stroke, hypertension, coronary heart disease, osteoporosis, and some cancers. Nutrients can also be essential (the body cannot make them) or nonessential. Cells absorb nutrients and use them in metabolic reactions. These include fueling reactions that create precursor metabolites and energy, biosynthetic reactions that turn precursor metabolites into building-block molecules, polymerizations that link those molecules into macromolecule polymers, and assembly reactions that use these polymers to build cellular structures.

**Nutritional groups** Organisms are classified by how they get carbon and energy. Heterotrophs consume carbon from other organisms; autotrophs make their own nutrients from inorganic carbon like carbon dioxide. Mixotrophs can act as both heterotrophs and autotrophs—examples include some plankton and carnivorous plants. Phototrophs get energy from light; chemotrophs get it from chemical energy in matter. Organotrophs take electrons from other organisms; lithotrophs take electrons from inorganic substances like water, hydrogen sulfide, dihydrogen, iron(II), sulfur, or ammonium. Prototrophs can create essential nutrients from other compounds; auxotrophs must consume preexisting nutrients.

**Diet** An organism’s diet is the total of foods it eats. A healthy diet boosts both physical and mental health. This requires taking in and absorbing vitamins, minerals, essential amino acids from protein, and essential fatty acids from fat. Carbohydrates, protein, and fat are major players in ensuring quality of life, health, and longevity. Some cultures and religions restrict what is acceptable in a diet.

**Nutrient cycle** A nutrient cycle is a biogeochemical cycle where inorganic matter moves through soil, organisms, air, or water, getting exchanged in organic matter. Energy flow is one-way and noncyclic, but mineral nutrients move in cycles. Mineral cycles include the carbon, sulfur, nitrogen, water, phosphorus, and oxygen cycles, among others, which continually recycle mineral nutrients into productive ecological nutrition. Biogeochemical cycles performed by living organisms and natural processes are water, carbon, nitrogen, phosphorus, and sulfur cycles. These cycles let essential elements return to the environment after being absorbed or consumed. Without proper nutrient cycling, oxygen levels, climate, and ecosystem function could change.

**Foraging** Foraging is the process of seeking out nutrients in the environment, and it can also include using those resources afterward. Some organisms, like animals and bacteria, can navigate to find food.