What Is the Function of Lactose?

Lactose is milk sugar. It's not as sweet as table sugar, but like table sugar, lactose provides your cells with energy when you eat it. You can use lactose for a number of other purposes, all of which it has in common with other carbohydrates like table sugar and starch.

Lactose in the Diet

The lactose molecule is classified as a carbohydrate, putting it in the same nutritional category as all the dietary sugars, as well as starch. Despite the fact that some carbohydrates taste sweet and others don't, all have the same number of calories -- 4 per gram consumed. Lactose tastes sweeter than starch but hardly as sweet as sugars like sucrose -- table sugar -- and fructose, which is fruit sugar.

Lactose Molecule

The lactose molecule is a disaccharide, meaning it's composed of two smaller sugar molecules called monosaccharides. These, specifically, are glucose -- a sugar that is ubiquitous in nature -- and galactose, which is less common. You can't absorb lactose, but instead break it into its monosaccharide constituents using digestive enzymes. You then absorb the monosaccharides into the bloodstream for cellular uptake, Dr. Lauralee Sherwood explains in her book "Human Physiology."

Uses Of Lactose

Because you can't absorb whole lactose, your cells can't use it. But they can use its component sugars, glucose and galactose. These give you a source of immediate energy, just as table sugar and starch do. Your cells can also convert the components of lactose into the storage carbohydrate glycogen, which provides a supply of sugar for periods of fasting, Drs. Reginald Garrett and Charles Grisham expalin in their book "Biochemistry." You can also convert the sugars into fat.

Lactose Considerations

None of the functions of the components of lactose are unique in the human body; you can do with sugars the same things you can do with lactose. For some people, however, lactose is unique in that they can't digest it. These people, who are lactose intolerant, experience digestive discomfort when they consume it as a result of it passing into the large intestine undigested, where bacteria break it down.

References (2)

  • Human Physiology; Lauralee Sherwood, Ph.D.
  • Biochemistry; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.

Photo Credits:

  • Maasdam Cheese and cheese with mould image by Galaiko Sergey from
