Nutrient

A nutrient is any substance an organism uses to survive, grow, and reproduce. Animals, plants, fungi, and protists all need dietary nutrients. These substances can be taken into cells for metabolism or expelled to build non-cellular structures like hair, scales, feathers, or exoskeletons. Some nutrients, such as carbohydrates, lipids, proteins, and fermentation products like ethanol or vinegar, can be broken down to release energy, with water and carbon dioxide as end products. Every organism needs water. Essential nutrients vary among organisms: animals require energy sources, certain amino acids, a few fatty acids, vitamins, and specific minerals; plants need a wider range of minerals absorbed through roots, plus carbon dioxide and oxygen from leaves; fungi obtain nutrients from living or dead organic matter. Nutrients can be organic (most carbon-containing compounds) or inorganic (everything else). For example, iron, selenium, and zinc are inorganic, while proteins, fats, sugars, and vitamins are organic. Ascorbic acid is essential for humans and some animals, but most other animals and many plants can produce it themselves.

A common classification for animal nutrition divides nutrients into macronutrients and micronutrients. Macronutrients—carbohydrates, fats, proteins, and water—are consumed in large amounts (grams or ounces) and are mainly used for energy or tissue growth and repair. Micronutrients—vitamins and minerals—are needed in tiny amounts (milligrams or micrograms) and play subtle roles in processes like vascular function and nerve conduction. A deficiency occurs when essential nutrients are lacking or absorption is impaired, harming growth, survival, and reproduction. Dietary guidelines, such as the U.S. Dietary Reference Intake, set lower and upper intake limits to prevent deficiency. Many countries require food labels to list significant amounts of macronutrients and micronutrients. Consuming too much of a nutrient can be harmful. Edible plants also contain thousands of phytochemicals, including polyphenols, whose effects on health or disease remain poorly understood as of 2024.

**Types**

**Macronutrients** are defined in several ways. The chemical elements humans consume most are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS). The compounds providing bulk energy are carbohydrates, proteins, and fats; water is also consumed in large amounts but has no calories. Calcium, sodium, potassium, magnesium, chloride, phosphorus, and sulfur are considered macronutrients because they are required in larger amounts than micronutrients. Macronutrients provide energy: carbohydrates are sugars classified by sugar units (monosaccharides, disaccharides, oligosaccharides, polysaccharides); proteins are amino acids linked by peptide bonds, with essential amino acids needing to come from diet; fats consist of glycerol and three fatty acids, which may be saturated or unsaturated, and are vital for cell membranes, body temperature, and skin and hair health—essential fatty acids must be obtained from food.

**Micronutrients** are essential dietary elements needed in varying amounts throughout life for metabolic and physiological functions. Dietary minerals like potassium, sodium, and iron are Earth elements that cannot be synthesized and are required in microgram or milligram amounts, obtained from plants or animals. Vitamins are organic compounds needed in microgram or milligram amounts; their importance was discovered when diseases appeared if they were missing from the diet.

**Essentiality**

An essential nutrient is one required for normal physiological function that the body cannot produce at all or in sufficient quantities, so it must come from diet. Apart from water, which is universally needed for homeostasis in mammals, essential nutrients are indispensable for cellular metabolism and tissue maintenance and function.