Simple sugars are carbohydrates. Glucose and fructose are monosaccharides and sucrose is a disaccharide of the two combined with a bond. Glucose and fructose have the same molecular formula (C6H12O6) but glucose has a six member ring and fructose has a five member ring structure.
Fructose is known as the fruit sugar as its make source in the diet is fruits and vegetables. Honey is also a good source.
Glucose is known as grape sugar, blood sugar or corn sugar as these are its riches sources. Listed in food ingredients as dextrose.
Sucrose is the sugar we know as sugar or table sugar. Typically extracted as cane or beet sugar. If sucrose is treated with acid or heat, it hydrolyzes to form glucose and fructose. This mixture of sucrose, glucose and fructose is also called invert sugar.
Nutritionally, these sugars are the same as they all provide 4 Cal/g. This is true for starch and other digestible carbohydrates too. Of the three sugars, fructose is the sweetest and glucose the least sweet, so typically less fructose can be used than table sugar (sucrose) – if sucrose has a sweetness of one, fructose is 1.7 and glucose 0.74
Fructose is more soluble than other sugars and hard to crystallize because it is more hygroscopic and holds onto water stronger than the others. This means that fructose can be used to extend the shelf life of baked products more than other sugars.