How do edible fats and oils differ in the amount of energy (kilojoules) they provide and how does this affect weight gain?

Any pure edible fat provides approximately 37 kilojoules (kJ) per gram. This is more than twice the energy level of one gram of protein or carbohydrate. As butter and margarine both contain some water (around 20%), they provide less than 30 kJ per gram. Cream contains even more water, so the energy content is usually less than 14kJ per gram. Cooking oils and fats generally contain little or no water, so they provide the full 37kJs per gram.

Although all pure fats provide about the same amount of energy, evidence shows that the effects of different fats differ according to their chemical composition. For instance, the degree of saturation influences the amount of weight gained or lost on an otherwise similar diet. Poly-unsaturated fats are less 'fattening' and may even be protective against obesity due to their varying influences on insulin resistance, metabolism and so forth.