The Obesity Code: Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight)

by Jason Fung

GLUCOSE, A SUGAR with the basic molecular structure of a six-sided ring, can be used by virtually every cell in the body. Glucose is the main sugar found in the blood and circulates throughout the body. In the brain, it is the preferred energy source. Muscle cells will greedily import glucose from the blood for a quick energy boost. Certain cells, such as red blood cells, can only use glucose for energy. Glucose can be stored in the body in various forms such as glycogen in the liver. If glucose stores run low, the liver can make new glucose via the gluconeogenesis process (literally meaning “making new glucose”). Fructose, a sugar with the basic molecular structure of a five-sided ring, is found naturally in fruit. It is metabolized only in the liver and does not circulate in the blood. The brain, muscles and most other tissues cannot use fructose directly for energy. Eating fructose does not appreciably change the blood glucose level. Both glucose and fructose are single sugars, or monosaccharides.