Sugars are crystallisable carbohydrates with oxygen and hydrogen existing in proportion to form water. There are several varieties of sugars, e.g., cane sugar, grape sugar, milk sugar, fruit sugar, and malt sugar. They present slight differences in their physical properties, such as specific gravity, solubility, and effect upon polarising light. They also differ in taste and digestibility.

Sugars have essentially the same use as starches, for all starch must be converted into glucose or dextrose before it can be made use of in the body.

Sugars are of value as energy and heat producers, and they also can be transferred into fat; they are, however, not essential for this purpose, as they can be replaced either by starches or fat They are largely used for preserving purposes. Thus, sugars and syrups are used to preserve fruits in solution, or in the dried form as preserved cherries and crystallised ginger.

Cane sugar requires to be converted into grape sugar before it is absorbed, and therefore grape sugar may be considered a predigested carbohydrate.

There has been a very striking increase in the consumption of sugar in recent years; the immoderate use of sugar gives rise to flatulent dyspepsia and disorders of nutrition (see Glycosuria).

There are three groups of sugars: -

1. Sucroses, or di-saccharids, examples of which are cane sugar, beet sugar, maple sugar, and malt sugar.

2. Glucoses, or mono-saccharids, grape sugar (dextrose), fruit sugar (levulose).

3. Invert sugar, best known as honey.