Glucose is the main outcome of carbohydrate digestion (80%) and constitutes the fundamental source of energy for cell metabolism. In minor quantities (about 20%), carbohydrate digestion also produces two other forms of sugars, galactose, and fructose. After gastrointestinal absorption, liver cells convert most galactose and fructose into glucose, through an enzymatic process known as monosaccharides interconversions. As the liver cells are rich in the enzyme glucose phosphatase, one of the metabolites of interconversion, glucose-6-phosphate, can be easily broken into glucose and phosphate, allowing glucose to pass through the hepatocytic membranes, thus entering the blood circulation. Therefore, 95% of circulating monosaccharides are glucose, the final conversion product.

Once in the blood circulation, glucose is transported to cells in the several body tissues, where it is transported through the cell membranes in association with molecules of protein carriers, a process known as facilitated diffusion...