Ever Wonder Why Some People Can’t Drink Milk?

By Howard J. Bennett

In the movie, “Finding Nemo,” a seahorse named Sheldon sneezed himself right off the screen after telling everyone he was H2O intolerant. The line got big laughs from most of the audience, but anyone younger than twelve may have missed the joke.

Although fish cannot be H2O (water) intolerant, lots of people have something with a similar sounding name—lactose intolerance—hence the joke in “Finding Nemo.” However, if you are lactose intolerant, you won’t sneeze. Instead, you’ll be bothered by one or more of the following symptoms: nausea, stomachache, burping, loose poops and farting.

This brings up two questions. First, what is lactose? Second, why are some people intolerant to the stuff?

Lactose is a type of sugar. It’s found in mammalian milk, which includes breast milk that babies drink and cow’s milk that kids drink. There are lots of other sugars, however. Besides lactose, the three most common sugars include the following:

• Fructose is the sugar found in fruit.

• Glucose is the main sugar your body uses for energy.

• Sucrose is used as a sweetener in candy and cereal. (If you see the word, sugar, on a food label, it means sucrose.)

Before I explain lactose intolerance, I need to review a bit about your intestinal tract. Food goes from your mouth, via your esophagus, to your stomach. After your stomach churns up what you’ve eaten and mixes it with digestive enzymes and hydrochloric acid, it pushes the gooey material (chyme, pronounced kime) into your small intestine.

The first part of the small intestine is called the duodenum (do-wad-in-um). The lining of the duodenum is covered with tens of thousands of fingerlike projections called villi. (Villi increase the absorptive surface of your small intestine by 40 to 50 times.) Lying within the villi are cells that make lactase, the enzyme that digests lactose.

If you don’t make lactase, any lactose you eat will pass undigested into your large intestine. Once lactose enters your large intestine, the bacteria that live there do you a “favor” and digest the milk sugar for you. Unfortunately, the byproducts released by these tiny creatures can make you sick, causing the symptoms I described earlier.

Lactose intolerance is not an all-or-nothing phenomenon. Some people are mildly lactose intolerant and can handle small amounts of milk sugar. Other people are severely intolerant and any amount of lactose will make them sick.

If you catch a stomach virus with vomiting and diarrhea, you may become temporarily lactose intolerant. This is why doctors usually recommend a milk-free diet for a few days after someone gets the “stomach flu.”

The best way to deal with lactose intolerance is to avoid milk sugar. Most people do this by drinking 100% lactose-free milk or taking lactase enzyme supplements before they eat yogurt, ice cream or cheese. If you forget, your rear end will remind you (and everyone else in the vicinity) that you did!


© 2012 Howard J. Bennett. All Rights Reserved.
(First published in the Washington Post 10/16/11.)

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