Fats

Fats, also known as lipids, are a broad class of organic molecules that are insoluble in water but soluble in organic solvents. In nutrition, fats commonly refer to triglycerides, but the category also includes phospholipids and sterols such as cholesterol. Fats provide concentrated energy, contribute to flavor and texture, and serve various roles in biology and metabolism.

Most dietary fats are triglycerides, molecules formed by glycerol esterified to three fatty acids. Fatty acids vary in chain length and degree of unsaturation. Saturated fats have no double bonds; unsaturated fats contain one or more double bonds and are further categorized as monounsaturated or polyunsaturated. Essential fatty acids, such as linoleic acid and alpha-linolenic acid, must be obtained from the diet.

Digestion and transport involve emulsification by bile salts, pancreatic lipase, and absorption of fatty acids and monoglycerides, which are reassembled into triglycerides and packaged into chylomicrons for transport via the lymphatic system and bloodstream. In tissues, fats are stored in adipose tissue, used for energy, and can be mobilized when needed.

Functions include energy storage (providing about 9 kcal per gram), insulation and protection of organs, and serving as major components of cell membranes through phospholipids. They are carriers for fat-soluble vitamins and precursors to signaling molecules such as eicosanoids.

Dietary considerations emphasize replacing saturated fats with unsaturated fats and avoiding most trans fats to reduce cardiovascular risk. Total fat intake is commonly advised to fit within a range of roughly 20-35 percent of daily calories, with emphasis on sources such as fish, nuts, seeds, and plant oils.

In mammals, adipose tissue stores energy as triglycerides. White adipose tissue predominates for energy storage, while brown adipose tissue dissipates energy as heat. Lipids also interact with cholesterol metabolism and lipoprotein transport, linking dietary fats to blood lipid profiles.