Polyunsaturated fatty acids, which are abundant in dietary oils, are degraded by oxygen, heat and light.
This phenomenon of rancidity may become dangerous due to the formation of complex compounds (hydroperoxides).This is why the addition of antioxidants to food is indispensable.
Fatty acids are the main constituents of lipids. The are characterised by the number of carbon atoms they possess, hence the expressions short-, mediumor long-chained fatty acids. They can be saturated (no double chemical bond between 2 carbons) or unsaturated (with 1 to 6 double bonds). Though the latter, more fragile, are subject to rancidity, theyinclude many fatty acids that are essential to vital functions.
Saturated fatty acids are exclusively energy sources (one talks about "empty" calories since they play no other role). Short-chain saturated fatty acids (6- 10 carbon atoms) are a very good source of fast energy for sports dogs, diabetic animals and newborn puppies. The function of polyunsaturated fatty acids is structural (in membranes or in blood lipoproteins); they include the omega 3 and omega 6 chemical series that have vital functions and cannot be synthesised by the body.
These are the same as for lipids: vegetable and animal oils and fats. The higher the unsaturated fatty acid content in the food, the greater the protection against oxidation (the increase in the antioxidant level – including vitamin E – is necessary).