Foods such as Potatoes, Rice, Peas, Bulk of Wheat and Other Grains; all comes under the category of Starch Foods. The starches can be digested only after they are turned into sugars in the body. If you put salt with sugar or starch, although it will mix perfectly and give its taste to the mixture, neither the salt nor the starch nor the sugar will have changed at all, but will remain exactly as it was in the first place, except for being mixed with the other substances. But if you were to pour water containing an acid over the starch, and then boil it for a little time, your starch would entirely disappear, and something quite different take its place. This, when you tasted it, you would find was sweet; and, when the water was boiled off, it would turn out to be a sugar called glucose. Again, if you should pour a strong acid over sawdust, it would “char” it, or change it into another substance, carbon. In both of these cases — that of the starch and of the sawdust–what we call a chemical change would have taken place between the acid and the starch, and between the strong acid and the sawdust.
If we looked into the matter more closely, we should find that what has happened is that the starch and the sawdust have changed into quite different substances. Starches are insoluble in water; that is, although they can be softened and changed into a jelly-like substance, they cannot be completely melted, or dissolved, like salt or sugar. Sugar, on the other hand, is a perfectly soluble or “meltable” substance, and can soak or penetrate through any membrane or substance in the body. Therefore all the starches which we eat — bread, biscuit, potato, etc. – have to be acted upon by the ferments of our SALIVA and our PANCREATIC JUICE, and turned into sugar, called glucose, which can be easily poured into the blood and carried wherever it is needed, all over the body. Thus we see what a close relation there is between starch and sugar, and why the group to which they belong is sometimes called the Starch-Sugars or Carbohydrates.