Lactose is milk sugar, a carbohydrate compound in milk and other dairy products. While it can provide your cells with energy, it's by no means an essential component of diet -- you don't need it to survive or thrive. If you're lactose intolerant, however, lactose is important because you need to avoid it.
Lactose
Lactose is a disaccharide compound, meaning it's made up of two smaller sugar units called monosaccharides. The monosaccharides that comprise lactose are called glucose and galactose, which your cells can burn for energy or store for later use. When you consume lactose, you have to digest it into its component monosaccharides using the enzyme lactase; you can then absorb them into the bloodstream.
Lactase
Enzymes, including lactase, are protein molecules that help regulate chemical reactions in the body and also help them take place faster than they otherwise would. Almost all babies and children -- and most adults -- produce lactase, meaning they can consume dairy products, break down the lactose, and use it for energy. Enzymes are very reaction-specific; if you don't make lactase, you have no way to break down lactose.
Lactose Intolerance
The group of humans to whom lactose is most important are those with lactose intolerance, simply because they must work so hard to avoid it. If you have lactose intolerance, you don't produce the lactase enzyme, so lactose passes undigested into the large intestine. There, bacteria break it down, which produces large amounts of gas and results in painful bloating and cramping. If you're lactose intolerant, you have to know which foods contain lactose -- essentially, that's any food with dairy in it -- and avoid them.
Uses of Lactose
Even though lactose isn't uniquely important to those without lactose intolerance -- other molecules can provide you with the same benefits lactose can -- you can use it as a source of energy. Once you've absorbed the monosaccharides from lactose, you can burn them immediately to provide your cells with energy, or store them for later energy use. One storage form is called glycogen, which is a carbohydrate made by the muscles and liver. Another storage form is fat, into which you can convert monosaccharides.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
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