Differences Between Simple Sugars & Starches

Simple sugars and starches are part of a large group of compounds known as carbohydrates. Sugars are monosaccharides, or single units of specific molecules such as glucose, fructose, and mannose. Starches, on the other hand, are polysaccharides, long chains of chains of single sugar molecule subunits linked together.

Close-up of a cake being sliced. (Image: eugenelucky/iStock/Getty Images)

Sugar Molecules

Simple sugars have a general chemical formula of CnH2nOn, where C stands for carbon, H stands for hydrogen, O stands for Oxygen, and n indicates a whole number. Glucose, for example, has the chemical formula, C6H12O6. There are two main types of simple sugars; aldoses, such as glucose, and ketoses, such as fructose.


Starches are made up of chains of sugar molecules linked together. The specific stereochemistry of their linkage is important. Starch molecules link glucose units together by alpha-1,4 and alpha-1,6 glucosidic bonds. Cellulose links glucose units together as well, but by beta-1,4 glucosidic bonds. In human cells, only the alpha-1,4 and alpha-1,6 bonds are recognized by enzymes involved in breaking down the starch. The beta-linkages are not. Even though both molecules are made of glucose, only starch can be digested, cellulose cannot.

Sources of Simple Sugars

Simple sugars are abundant in the average American diet. They are readily found in such processed foods such as sodas, cakes, cookies, and ice-cream. However, simple sugars are also found in unprocessed foods such as fruits and honey. They provide a quick source of energy to cells. In excess, however, simple sugars are converted to stores of energy, or fat.

Sources and Uses of Starch

Sources of starch in the diet include rice, breads, potatoes, and corn. Unlike simple sugars, in order to use the energy of the sugar molecules in the starch, the body has to first break down the links between each sugar subunit. Thus, eating something starchy does not give as quick of an energy rush as eating a simple sugar; it takes time to digest the linkages.

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