Lipid

Lipid is a broad group of biological substances with common properties: they do not dissolve in water or dissolve poorly in it, but they do dissolve in organic solvents such as ether and chloroform. This group includes fats, oils, waxes, phospholipids, and sterols such as cholesterol.

Lipids are one of four major groups of biological molecules, alongside proteins, carbohydrates, and nucleic acids. Their primary functions are energy storage, formation of the cell membrane, and acting as hormones and signaling molecules within the body.

Chemical structure

Most lipids consist of chains of carbon and hydrogen (fatty acids). Fatty acids are classified as saturated or unsaturated, depending on whether there are double bonds between the carbon atoms. Fats from plants typically contain unsaturated fatty acids and are therefore liquid at room temperature; animal fats are typically solid.

The most common form of lipid in food and body storage is the triglyceride: three fatty acids attached to a single glycerol molecule. Phospholipids have a water-loving part (the phosphate head) and a water-repelling part (the fatty acid tails), allowing them to form a bilayer that makes up the cell membrane.

Function in the body

Each gram of lipid provides more energy than a gram of carbohydrate or protein, making it an efficient, compact form of energy storage. Lipids also carry fat-soluble vitamins A, D, E, and K. Cholesterol serves as a precursor for synthesizing steroid hormones and bile acids and is transported in the blood as lipoproteins (LDL and HDL).

Health and nutrition

The amount and type of dietary lipid are associated with blood cholesterol levels and risk of heart and vascular disease. Trans fats produced by industrial hydrogenation of oils are recommended for reduction by health authorities. Abnormalities in lipid metabolism are also associated with conditions such as obesity and type 2 diabetes.