Lactose is a sugar that some individuals have trouble digesting. This condition, called lactose intolerance, leads to uncomfortable digestive symptoms upon consumption of lactose. If you're lactose intolerant, you can drink milk that's lactose free. Rather than remove all the lactose from milk, manufacturers use chemicals to modify the lactose.
Lactose
Lactose is a kind of sugar, closely related but not identical to table sugar. Sugars all consist of one or two chemical units called monosaccharides. Lactose and table sugar each have two monosaccharides chemically bonded together -- to absorb the monosaccharides from these sugars, you have to digest lactose and separate them from one another using digestive enzymes. The two monosaccharides in lactose are called glucose -- this is the most common monosaccharide -- and galactose, which is similar in structure. This process is mimicked to make lactose-free milk.
Lactose-Free Milk
Because many lactose-intolerant individuals enjoy milk and other dairy, some manufacturers produce lactose-free milk. It's quite difficult to remove the lactose from milk, and doing so would change the taste and the nutritional content tremendously. Instead, manufacturers "chemically digest" the lactose, splitting it into glucose and galactose. In her book "Human Physiology," Dr. Lauralee Sherwood explains that you can absorb glucose and galactose directly -- you don't need to digest them -- meaning that even if you're lactose-intolerant, you can handle glucose and galactose.
Adding Lactase
To chemically digest lactose, manufacturers add an enzyme called lactase to the milk and allow it to process for about 24 hours, explains OrganicMeadow.com, a lactose-free milk producer. Enzymes are proteins that help chemical reactions take place faster than they otherwise would. If you're lactose-intolerant, it's because you lack the lactase enzyme. By adding lactase to the milk and allowing the enzyme to "pre-digest" the lactose, it makes the milk easily digestible to you.
Other Considerations
Often, lactose-free milk tastes sweeter than regular milk. This is because lactose doesn't bind strongly to the sweetness receptors in your mouth, but glucose does. Many lactose-free dairy products like lactose-free ice cream have had the lactose modified in the same way as lactose-free milk, meaning they're safe for you if you're lactose-intolerant. Most individuals with lactase deficiencies can consume yogurt without it having been chemically modified, since the bacteria that produce the yogurt pre-digest most of the lactose.
Lactose Intolerance
The reason you can consume lactose-free milk even if you're unable to consume normal dairy is that lactose intolerance isn't an allergy -- it's simply an inability to digest the sugar in milk. Enzymes in the digestive tract are very specific -- the enzymes that digest table sugar, for instance, aren't the same as those that digest proteins, carbohydrates or milk sugar. As such, by chemically digesting the lactose, milk is modified in such a way that it no longer contains any component you aren't able to process.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- OrganicMeadow.com: Lactose-Free Milk
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