Science Education

Breaking Down Lactose Intolerance

Whenever I drink milk, I get really gassy for no reason. I don’t understand: I’ve been drinking milk since I was a baby and it never bothered me before. Could it be that GMO thing I keep hearing about?

No. It most probably has nothing to do with genetically-modified organisms but rather with lactose intolerance.

What’s lactose?

Cow milk is not some miracle substance worthy of a special spot in the periodic table of elements. It is a mixture of proteins, fat, sugars, salts, vitamins, and minerals in water. Lactose is one sugar found in milk. At the molecular level, lactose is composed of two simple sugars bound together: glucose and galactose.

Oh, I see. So what’s lactose intolerance?

In order to absorb lactose into your bloodstream, the chemical bond between glucose and galactose needs to be severed. This surgical cut is made by an enzyme called lactase. When you see a word that ends in “-ase”, it’s usually an enzyme. Lactase is made by the human body, specifically the small intestine.

Problems arise when the body stops producing this enzyme.

Why do we stop producing this enzyme?

For a long time, human beings would naturally lose the ability to synthesize lactase after weaning, since there was no use to producing an enzyme that would serve no purpose. However, when cattle began to be domesticated, there was an advantage to continue producing lactase into adulthood, as milk is a fairly rich food which was quickly becoming more commonplace. Natural selection favoured those individuals who had a mutation that led to the sustained regulation of the gene which codes for lactase well into adulthood. This phenomenon is known as “lactase persistence”, but it does not, unfortunately, affect everyone.

So what happens to the lactose if it’s not digested by lactase?

The lactose does not leave your digestive tract to enter blood circulation. Rather, it continues on down to your colon where it is swallowed up by bacteria which can further process it. The problem is that, as they do, they release gas as a by-product, which means that your colon starts to inflate.

Is this dangerous?

No, simply uncomfortable and sometimes painful.

Can I do anything to avoid this? Gas is so not cool.

You can avoid dairy products, like milk, butter, cheese, yogurt, ice cream, and any processed food that contains “modified milk ingredients”, “whey powder”, “casein”, or “lactose”. While whey and casein are milk proteins, you don’t know how they were purified from milk and whether or not some lactose might be present. If you are only lightly intolerant to lactose, you may be able to digest the lactose found in cheese and yogurt, as the bacteria required for their fermentation tend to digest some of it, leaving fewer intact molecules of lactose in the final product. Avoiding dairy altogether, though, means you need to make sure you get enough calcium in your diet.

If you really want to indulge in dairy products, you can purchase tablets of the lactase enzyme. You can pop these pills before eating dairy: the enzyme will digest the lactose just as it would if your body were to produce it. Lactase tablets are available in most drugstores. Otherwise, certain dairy products are available in “lactose-free” form. The manufacturer pre-digested the lactose with lactase for you, so you can safely indulge in these.

What about eggs? Can I eat eggs?

Yes. Eggs do not contain lactose.

What about margarine? And dark chocolate? Are those OK?

Always check the ingredients list on the food you buy if you know you are lactose intolerant. Some margarines do contain milk ingredients, while others stick to vegetable oils. The same applies to dark chocolate: you would think that “dark” means “without milk”, but many manufacturers are adding milk to their dark chocolates to make them creamier.


That sounds stupid.

It is, it is. Don’t trust the front of the packaging. Always read the ingredients.


(Feature picture by perez-tonella)

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