Food Science: What is Lactose Intolerance?

Food Science: What is Lactose Intolerance?

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Emma Christensen
Jan 27, 2009

More and more of us seem to be succumbing to lactose intolerance these days. And while having a built-in deterrent to eating lots of cheese and ice cream might seem like a boon if you're trying to watch your weight, intolerance to milk products definitely presents its own set of difficulties! So what's going with lactose intolerance and how does it happen in the first place? Read on...

It all comes down to one sugar in the milk called, predictably, "lactose." Young or old, our bodies can't actually absorb lactose as it is, and so we need another enzyme to break it down for us. Without this enzyme, digesting lactose causes gas, bloating, and possibly diarrhea.

This friendly digestive enzyme, "lactase," is present in high levels shortly after birth, but then slowly declines over the next several years. At 2-5 years of age, the levels of lactase reach an average minimum, which is where it pretty much stays through adulthood. The biological reason for this is that humans don't actually need milk after they're weaned and so the body stops producing the enzyme to digest it.

Here's where it gets interesting though! Several thousand years ago, there was a genetic change in some northern European populations that allowed them to continue producing lactase after infancy. In the cold climates where these populations were living, milk was a significant nutritional resource throughout life and the ability to digest it took on evolutionary importance.

This is why people today with northern European ancestry are generally able to easily digest milk and milk products, but people from other parts of the world generally are not. There are obviously exceptions to every rule, but what's important to realize is that the ability to digest milk after infancy is the exception rather than the rule.

Luckily, lactose intolerance doesn't actually mean you can't consume any milk or milk products at all. (Milk intolerance and milk allergies are separate conditions.) Adults with lactose intolerance still have a base level of lactase in their digestive systems, and they can generally consume about a cup of milk per day without any...er...ramifications.

There are also many milk products that don't present digestive difficulties to people with lactose intolerance. Hard or aged cheeses like parmesan and pecorino have little lactose and can be digested easily. Fermented milk products like yogurt and buttermilk can also usually be consumed because they contain a bacteria that assists in lactose digestion.

What has been your experience with lactose intolerance?

Related: On Cooking with Restrictions

(Image: Flickr member Bowena licensed under Creative Commons)

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