Carbohydrates consist of single-sugar units called monosaccharides, double-monosaccharide units known as disaccharides and multiple-monosaccharide molecules that make up starches. The predominant purpose of the carbohydrates you eat is to provide fuel to your cells. Disaccharides and starches undergo digestion to reduce them to their individual sugars, and, once absorbed, they travel to the cells and tissues throughout your body to power your physical activities. Proteins consist of 20 different amino acids, mixed and matched to create a vast array of larger molecules that support every process in your body. Digestion of protein results in a pool of single amino acids that your cells incorporate into new proteins as the need arises in your body. These molecules make up muscles and organs, transmit signals between cells, constitute immune molecules, help create the new proteins your tissues require and can serve as a fuel source in a pinch. Your cells contain two types of nucleic acids, ribonucleic acid and deoxyribonucleic acid, or RNA and DNA, respectively. They differ from the other macronutrients in that they are not a source of calories in your diet, and their role is strictly to direct the synthesis of new protein molecules. Made up of units called nucleotides, the nucleic acid DNA contains the genetic blueprint that influences your personal characteristics, while the nucleic acid RNA pulls together amino acids to form new proteins as your cells need them.
