Peter Barham writes: “Many people seem to think there is some great difference between a ‘fat’ and an ‘oil’. There is no real difference. We just happen to use the term ‘oil’ for those materials that are liquid at room temperature, and call those that are solid at room temperature ‘fats’. The distinction is thus rather arbitrary. Since we nearly always melt fats when we cook with them they should be called ‘oils’ in use.
All fats and oils produced by plants and animals are used to store energy. The molecular structure of oils and fats is very similar to that of the fuel you use to power your car. Just as with the petrol in a car engine, the energy is released when the fat is ‘burnt’. Burning, in this context, really means ‘oxidation’; the reaction of the fat with oxygen. …in our bodies we manage to carry out the reaction more slowly [than petrol in a car engine] in a controlled fashion so that the heat is not so concentrated, but nevertheless a similar amount of energy is liberated.”
Ref: p.10 Peter Barham (c2001) The Science of Cooking. Springer-Verlag: Berlin