Lipids are long hydrocarbon (H, C, O) chains found in both plants and animals. They are insoluble in water. Lipids fall into one of three main groups:

Simple lipids - e.g. triglycerides

Compound lipids - e.g. lipoproteins (LDL & HDL)

Derived lipids - e.g. cholesterol, steroids

Triglycerides are the storage form of fat in the body (glycerol + 3 fatty acid molecules). There are two forms of fatty acid molecule, namely saturated and unsaturated fat. Saturated fat has the most number of Hydrogen atoms possible and is said to be monounsaturated with its single hydrogen bonds. Fats with double hydrogen bonds are said to be polyunsaturated and better for health.

The main category of compound lipids are the Lipoproteins. These are made with the joining of proteins and transport lipids in the blood. Low-density lipoprotein (LDL) delivers cholesterol to the arterial tissue where too much sticks to the artery walls. High-density lipoproteins on the other hand transports cholesterol to the liver to be mixed with waste products and secreted. HDLs are increased with exercise, altering the LDL:HDL ratio.

Derived lipids are mainly made up of steroid groups, an example of which is cholesterol. In minute quantities these perform major roles in the body. Lipids provide the largest nutrient store of potential energy for biological work. They protect vital organs and provide insulation from the cold. Lipids act as the carrier for the fat-soluble vitamins A, D, E and K.

During light and moderate intensity exercise, lipids contribute about 50% of energy for exercise. As exercise is prolonged this increases with fatty acid molecules providing more than 80% of energy requirements.