Overview

Lipids are a diverse family of naturally occurring organic molecules that are generally insoluble in water but soluble in nonpolar solvents. They are widely found in living organisms and include edible fats and oils as well as structural components of cells. Common dietary sources include algae, seeds, meat and dairy; some microscopic organisms such as algae are especially rich in certain lipid types.

Structure and classification

At the chemical level many lipids are long chains or rings composed primarily of carbon and hydrogen, often with oxygen, phosphorus or nitrogen atoms attached. Lipids are grouped by structure and function into several major classes rather than a single chemical family. Simple lipids include triglycerides (fats and oils) and waxes; complex lipids include phospholipids and glycolipids; sterols and steroid derivatives form another important category. Examples of complex membrane components are phospholipids, which contain both polar and nonpolar regions.

Common types

  • Fats (triglycerides) – esters of glycerol and fatty acids used mainly for energy storage.
  • Waxes – long-chain esters serving protective and waterproofing roles in plants and animals.
  • Phospholipids – amphipathic molecules that organize into bilayers in water.
  • Fat‑soluble vitamins (A, D, E, K) – small lipid-soluble molecules with specialized biological roles.
  • Sterols and steroid hormones – rigid ring structures that modulate membrane properties and act as signaling molecules.

Biological functions

Lipids play several essential roles in biology. A primary structural role is forming lipid bilayers, the basic framework of cell membranes, where amphipathic lipids arrange so that polar head groups face water and nonpolar tails face inward. Lipids also serve as concentrated energy reserves, provide thermal insulation, and form barriers such as plant cuticles and insect exoskeleton coatings. Certain lipids act directly in signalling, either as hormones, second messengers or precursors for signaling molecules.

Metabolism, diet and health

Dietary lipids are digested and absorbed as fatty acids and monoacylglycerols, reassembled into triglycerides for storage, or converted into membrane components and signaling lipids. The physical properties of lipids—saturation level of fatty acid chains and chain length—affect their melting point and biological behavior. In human health, different lipid patterns correlate with metabolic risk factors; however, lipids are essential nutrients and many have beneficial roles, such as fat‑soluble vitamins and essential fatty acids that must be obtained from the diet.

History and scientific importance

Scientists began recognizing and characterizing lipids during the 18th and 19th centuries as chemists separated animal and plant oils and studied fatty acids, glycerol and sterols. Today lipids are studied across biochemistry, cell biology and nutrition for their central roles in membrane architecture, energy balance and intercellular communication. For further reading on biochemical pathways, classification and applied uses see specialized resources and reviews on carbon‑based biomolecules and summaries of lipid classes and properties.

Notes: lipids are not a single polymeric class but a practical grouping of hydrophobic and amphipathic compounds; terminology overlaps with everyday words such as "fat" and "oil," which are often used with different meanings in nutrition and chemistry.

Additional references and educational materials: definition, occurrence, biological sources, membrane components, bilayer structure, cell membranes, triglycerides, waxes, fat‑soluble vitamins, lipid signalling, chemical composition, physical properties.