plural: fats
fats, fæts
A term largely applied to storage lipids in animal tissues that are usually solid at room temperature



Fat is a triglyceride (a type of lipid) that is usually solid at room temperature. Hence, it will be inaccurate to consider the two terms synonymous. Fats are a type of lipid (other types of lipids are fatty acids, glycerol, glycerophospholipid, sphingolipid, sterol lipid, and lipid). By definition, a lipid is a fatty or waxy organic compound that is readily soluble in nonpolar solvent (e.g. ether) but not in polar solvent (e.g water). In food science though, fat and lipid are regarded the same or synonymous. However, in strict sense, fats are different from lipids as fats are lipids but not all lipids are fats. Oil is also different from fat. Oil is also a type of lipid. However, contrary to fat, oil does not solidify at room temperature. That is because the oil is comprised of short or unsaturated fatty acid chains, which when at room temperature, remains liquid.


Fat is comprised of fatty acids. A fatty acid pertains to any long chain of hydrocarbon with a single carboxylic group and aliphatic tail. Thus, fats belong to a group of molecules, the hydrocarbons. Similar to other lipids, fats are soluble in organic solvents and insoluble in water. Fats are generally hydrophobic.
As for the structure, fats are derived from fatty acids and glycerol. Fatty acids pertain to any of the group of a long chain of hydrocarbon with a carboxylic acid at the beginning and a methyl end. They may be classified based on the nature of covalent bond: (1) unsaturated fatty acid and (2) saturated fatty acid. The fatty acid component of fat molecules is mostly saturated. Saturated fatty acids lack unsaturated linkages between carbon atoms. This means that saturated fatty acids cannot absorb additional hydrogen atoms in which unsaturated fatty acids can. Fats are solid at room temperature because they are mostly comprised of long hydrocarbon chains or saturated fatty acids. The long hydrocarbon chains tend to form intermolecular attraction (particularly, van der Waals forces). Saturated fats stack in a tightly packed arrangement and therefore solidify rather easily at room temperature.
The fatty acid constituent of a fat molecule may also vary in length. A fatty acid with aliphatic tail of five or fewer carbons is called a short-chain fatty acid. Medium-chain fatty acid is one that has an aliphatic tail of 6 to 12 carbons. A long-chain fatty acid is one that has an aliphatic tail of 13 to 21 carbons. A fatty acid with an aliphatic tail of 22 or more carbons is called very long chain fatty acid. When the fatty acid chains are glycerated, the resulting fat molecule may therefore have varying lengths. Nevertheless, most dietary fats have medium to longer chains of fatty acids of equal (or nearly equal) length. Lard, for example, would have long hydrocarbon chains, i.e. about 17 carbons long.


Examples of fats are cholesterol, phospholipids and triglycerides. Cholesterol is a sterol or a modified steroid that is synthesized by animal cells to become an essential component of animal cell membranes. Because of cholesterol that provides cell membrane structural integrity and fluidity, animal cells need not to have cell walls such as that in bacterial and plant cells. Cholesterol in animal cell membranes also enables the animal cells to change shape and therefore are rather flexible than plant cells (which are less flexible in shape due to the presence of the cell wall). A phospholipid is a lipid consisting of a glycerol bound to two fatty acids and a phosphate group. Phospholipids serve as a major structural component of most biological membranes. They form the lipid bilayer in cell membranes of organisms. Examples of phospholipids include phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, lecithin, plasmalogens and sphingomyelins. A triglyceride is a glycerol with three fatty acids attached by ester bonds. As such, it would apparently resemble a letter “E”. Animal triglycerides are important energy source and present in adipose tissues, bloodstream, and heart muscle.
Dietary fats are exemplified by essential fatty acids (EFAs). They are referred to as essential because they are not easily synthesized in the body and therefore are obtained in the diet. Two major groups of EFAs in human nutrition are alpha-linoleic acid (an example of omega-3 fatty acid) and linoleic acid (an example of omega-6 fatty acid).

Common biological reactions

Common biological reactions

Fats are derived from fatty acids. Fatty acids form fats through dehydration synthesis and the formation of ester bonds. This process is referred to as esterification, which makes fats an ester. Triglyceride, for instance, forms when each of the three chains of fatty acid is attached to the –OH group of the glycerol and the concomitant release of water in the process.

Common biological reactions

Dietary fats are digested and degraded into fatty acids and glycerol through hydrolysis. In humans, the digestion of dietary fats involves the breaking down of fats by the enzyme lipases produced in the pancreas.

Biological importance

Fats are an important source of energy. They are one of the major energy sources that can be derived from the diet. Some lipids, such as EFAs, are not synthesized in the body from simpler constituents and therefore are derived from the diet. Thus, fat is an essential nutrient as they are an important energy source. Compared with carbohydrates, fats are more energy dense. Fat contains twice as much energy as a carbohydrate, and is stored by the body due to this. The heart and skeletal muscles prefer fatty acids. The degradation of fat releases fatty acids and glycerol. Glycerol can further provide energy when it is converted into glucose in the liver. Excess fats are stored in adipose tissue. The adipose tissue containing stored fats provides cushion and insulation. The fat tissue thereby protects the body against certain injuries and helps regulate body temperature during cold.


Derived term(s)

  • Buccal fat-pad
  • Fat body
  • Fat body of ischiorectal fossa
  • Fat body of orbit
  • Fat body of cheek
  • Fat cell
  • Fat droplet
  • Fat graft
  • Fat emulsions intravenous
  • Fat embolism
  • Fat indigestion
  • Fat metabolism
  • Fat necrosis
  • Fat necrosis tumour
  • Fat-soluble vitamin
  • Wool fat

Further reading


See also

  • lipid
  • fatty acid

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