Of the twenty amino acids, eight are called essential. Essential amino acids must be provided by your diet. Carbohydrates Carbohydrates provide a major source of energy for the body and are used to power muscular contraction and as a fuel for the central nervous system. Carbohydrates spare protein from being synthesized into glucose, and they are a metabolic primer for fat metabolism. Monosaccharides and disaccharides are also called simple sugars or simple carbohydrates, and polysaccharides are called complex carbohydrates.
Complex carbohydrates are starch, glycogen, and cellulose.
Regardless of the original form of a carbohydrate, the liver converts them into glucose which is blood sugar. Some glucose is stored in the liver and muscles as glycogen, some is used as energy, and some is converted into fat. Lipids Fats are the chief storage form of energy in the body. Fat insulates and protects vital organs, and provides fat-soluble vitamins. Fat molecules are made up of simpler units called fatty acids.