A nutrient is anything an organism uses to survive, grow, and reproduce. The need to consume nutrients in food applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or removed from cells to form non-cellular structures such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically broken down into smaller molecules in energy-releasing processes, such as carbohydrates, lipids, proteins, and fermentation products (ethanol or vinegar), producing end-products such as water and carbon dioxide. All organisms need water. Essential nutrients for animals include energy sources, certain amino acids that combine to form proteins, a subset of fatty acids, vitamins, and some minerals. Plants also require various minerals absorbed through their roots, as well as carbon dioxide and oxygen absorbed through their leaves. Fungi live on dead or living organic matter and obtain their nutrient requirements from their host.
Different organisms have different essential nutrients. Ascorbic acid (vitamin C) is essential for humans and some animal species, but most other animals and many plants can synthesize it. Nutrients can be organic or inorganic: organic compounds include most carbon compounds, while all other chemicals are inorganic. Inorganic nutrients include nutrients such as iron, selenium, and zinc, while organic nutrients include proteins, fats, sugars, and vitamins.
One classification used to describe the nutrient requirements of animals divides nutrients into macronutrients and micronutrients. Macronutrients (carbohydrates, fat, protein, water), consumed in large quantities (grams or ounces), are primarily used to create energy or incorporated into tissues for growth and repair. Micronutrients are needed in smaller quantities (milligrams or micrograms); they play minor biochemical and physiological roles in cellular processes, such as vascular function or nerve conduction. Low levels of essential nutrients or diseases that interfere with absorption lead to deficiencies that affect growth, survival, and reproduction. Consumer advisories for dietary nutrients, such as the United States Dietary Reference Intake, are based on the amount needed to prevent deficiency and provide macronutrient and micronutrient guides for both lower and higher intake limits. In many countries, regulations require food product labels to provide information about the amount of any macronutrient and micronutrient present in the food. Excess nutrients can have harmful effects. Edible plants also contain thousands of compounds, commonly called phytochemicals, that have unknown effects on disease or health, including a separate group of non-nutrient compounds called polyphenols, which are not well understood as of 2024.
Types of Nutrients
Macronutrients
Macronutrients are described in many ways.
The chemical elements that humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, called CHNOPS.
The chemical compounds that humans consume in the largest quantities and from which they provide the most energy are classified as carbohydrates, proteins, and fats. Water should also be consumed in large quantities, but it does not provide calories.
Calcium, sodium, potassium, magnesium, and chloride ions, along with phosphorus and sulfur, are included in macronutrients because their needs are greater than those of micronutrients, i.e., vitamins and other minerals, often called trace or ultratrace minerals.
Macronutrients provide energy:
Carbohydrates are compounds made up of different types of sugars. Carbohydrates are classified according to 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 consisting of amino acids linked by peptide bonds. Because the body cannot make some amino acids (called essential amino acids), they must be obtained from food. During digestion, proteins are broken down into free amino acids by proteases.
Fats consist of a glycerin molecule to which three fatty acids are attached. Fatty acid molecules contain a -COOH group attached to an unbranched hydrocarbon chain that is either linked by a single bond (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are essential for the formation and maintenance of cell membranes, maintaining body temperature, and maintaining skin and hair health. Because the body doesn't make some fatty acids (called essential fatty acids), they must be obtained from food.
Micronutrients
Micronutrients are essential dietary elements that are required in varying amounts for metabolic and physiological functions throughout life.
Dietary minerals, such as potassium, sodium, and iron, are elements found in the earth and cannot be synthesized. Their requirements in the diet are expressed in micrograms or milligrams. Just as plants obtain minerals from the soil, dietary minerals are obtained directly from plants or indirectly from the animals they eat.
Vitamins are organic compounds that are required in micrograms or milligrams. The importance of each dietary vitamin became apparent when it was discovered that a deficiency of that vitamin can cause disease.
Essential Nutrients
An essential nutrient is one that is essential for normal physiological function, that the body cannot produce at all or in sufficient quantities, and therefore must obtain from food. In addition to water, which is universally required to maintain homeostasis in mammals, essential nutrients are required for various cellular metabolic processes and the maintenance and function of tissues and organs. Nutrients considered essential for humans include nine amino acids, two fatty acids, thirteen vitamins, fourteen minerals, and choline. Additionally, several molecules are considered conditionally essential nutrients because they are required in certain developmental and pathological conditions.
Amino Acids
An essential amino acid is an amino acid that an organism needs but cannot make on its own, and therefore must obtain it from food. Of the twenty standard protein-forming amino acids, humans cannot make nine: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.
Fatty Acids
Essential fatty acids (EFAs) are fatty acids that humans and other animals must consume because the body needs them for good health, but the body cannot make them. Only two fatty acids are considered essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
Vitamers and Vitamers
Vitamers exist in several similar forms called vitamers. Vitamers of a given vitamin perform that vitamin's function and prevent deficiency symptoms. Vitamins are essential organic molecules that are not categorized as amino acids or fatty acids. They typically function as enzymatic cofactors, metabolic regulators, or antioxidants. Humans require thirteen vitamins in their diet, most of which are actually groups of similar molecules (e.g., vitamin E includes tocopherols and tocotrienols): vitamins A, C, D, E, K, thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12). Vitamin D requirement is conditional, as people exposed to excessive ultraviolet light from the sun or artificial sources produce vitamin D in their skin.
Minerals
Minerals are foreign chemical elements essential for life. Although the four elements carbon, hydrogen, oxygen, and nitrogen (CHON) are essential for life, they are so abundant in foods that they are not considered nutrients and mineral intake is not recommended. Nitrogen provides the necessary nutrients for protein, which is made up of nitrogen-containing amino acids. Sulfur is essential, but again, it is not recommended. Instead, the sulfur-containing amino acids methionine and cysteine are recommended.
The essential nutrient trace elements for humans, listed by dietary requirement (indicated in mass), are potassium, chloride, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, and selenium. Additionally, cobalt is a component of vitamin B12, which is essential. There are other minerals that are essential for some plants and animals, but may or may not be essential for humans, such as boron and silicon.
Choline
Choline is an essential nutrient. Choline is a family of water-soluble quaternary ammonium compounds. Choline is the parent compound of the choline class, containing three methyl substituents linked to ethanolamine and amino functions. Healthy humans who consume artificially engineered foods lacking choline develop fatty liver, liver damage, and muscle damage. Choline was not originally considered essential because the human body can produce small amounts of choline through phosphatidylcholine metabolism.
Conditionally Essential Nutrients
Conditionally essential nutrients are organic molecules that an organism can normally produce, but in small quantities under certain conditions. In humans, these conditions include premature birth, low nutrient intake, rapid growth, and certain diseases. Inositol, taurine, arginine, glutamine, and nucleotides are classified as conditionally essential and are particularly important for the nutrition and metabolism of the newborn.









