Simple carbohydrates are sugars whose bonds are easily broken down by digestion. Sugars are classified as mono- (one) or di- (two) saccharides.
Monosaccharides are glucose, fructose and galactose. The body can only absorb the monosaccharides into the bloodstream, but only glucose affects blood sugar levels, and therefore all other carbohydrates that are consumed are converted to this usable form in the body. Glucose can be obtained through digestion or through the process of gluconeogenesis. Fructose, also known as fruit sugar, has the same chemical composition of glucose, but has a different shape. Upon absorption into the bloodstream, it is transported to the liver, where it is metabolized to form glucose. Galactose does not exist freely in nature but can be found combined with glucose in milk. The 5-carbon monosaccharide ribose is an important driver of the coenzymes involved in energy production, including adenosine triphosphate (ATP), flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NAD). It is also an integral part of the genetic molecules of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Disaccharides are two monosaccharides bonded together and include maltose (two glucose molecules), sucrose (fructose and glucose) and lactose (galactose and glucose). Maltose is found in beer, cereals and seeds, whereas sucrose, commonly known as table sugar, is found in cane sugar, honey and maple syrup. Lactose is the only sugar not found in plants; it is found in milk.