What are lipids?
Oils and fats both belong to one group: lipids. The difference between them is not chemistry but temperature.
Fat
Solid at room temperature.
Oil
Liquid at room temperature.
Chemical composition
As with carbohydrates, lipids contain carbon (C), hydrogen (H) and oxygen (O).
So what is different?
In a carbohydrate the H : O ratio is always exactly 2 : 1. In a lipid that ratio is always greater than 2 : 1 — there is relatively less oxygen.
Why lipids yield more energy
Because there is less oxygen, there is more hydrogen left to burn.
Solubility
- Lipids do not dissolve in polar solvents, including water
- But they do dissolve in organic solvents
This insolubility in water is what lets lipids build cell membranes and keep water out.
How lipids are formed
Fatty acids + glycerol → lipid + water
As with disaccharide formation, a molecule of water is released.
Lipid-rich foods
- Peanuts
- Coconut
- Sesame
- Margarine
- Vegetable oils