WEBVTT - Are Humans Built to Drink Milk as Adults?

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<v Speaker 1>Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,

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<v Speaker 1>Lauren Bogle Bomb here. When people can't digest milk, we

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<v Speaker 1>call them lactose intolerant. This seems to signify that it's

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<v Speaker 1>an unusual condition, that most people are just fine with milk,

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<v Speaker 1>cheese and ice cream, and that lactose intolerance is something

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<v Speaker 1>that needs to be fixed or helped. But it turns

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<v Speaker 1>out that those poor souls who get gassy, crampy, and

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<v Speaker 1>otherwise digestively miserable after eating dairy products are actually in

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<v Speaker 1>the majority worldwide. It's the people who can handle milk

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<v Speaker 1>who are the weird ones. Lactose is the main form

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<v Speaker 1>of sugar in all mammal milk, and everyone is born

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<v Speaker 1>with the gene that codes for the creation of lac taste,

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<v Speaker 1>which is the enzyme that processes lactose. When we're babies,

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<v Speaker 1>in other words, we all have the ability to digest milk.

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<v Speaker 1>The small intestine produces lac taste. It breaks down lactose

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<v Speaker 1>into glucose and galactose, which can be easily absorbed into

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<v Speaker 1>the bloodstream. But for reasons unknown, the lactaste gene tends

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<v Speaker 1>to shut off about the time we're weaned from breast milk.

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<v Speaker 1>Most people don't create any lactaste, or very little of

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<v Speaker 1>it by the time they're five years old or so.

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<v Speaker 1>In the absence of lactaste, undigested lactose just sits in

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<v Speaker 1>the colon and ferments, causing all kinds of uncomfortable side effects. Basically,

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<v Speaker 1>your gut bacteria eat it and they excrete gas and

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<v Speaker 1>other wastes, which you then have to excrete. Some people, however,

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<v Speaker 1>carry a genetic mutation that allows the lactaste gene to

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<v Speaker 1>keep working. Sometimes it continues for just a few more years,

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<v Speaker 1>sometimes for a lifetime. Of Americans have a functional lactaste gene,

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<v Speaker 1>so in the United States it is unusual to be

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<v Speaker 1>lactose intolerant, but worldwide, more than six people lose the

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<v Speaker 1>ability to process lactose. Because lactose intolerance is the more

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<v Speaker 1>common condition around the globe, scientists and researchers in the

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<v Speaker 1>field actually use the term lac taste persistence for people

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<v Speaker 1>who can digest milk. Certain populations are more prone to

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<v Speaker 1>lac taste persistence than others. In the United States, people

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<v Speaker 1>of Caucasian descent are much more likely to be able

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<v Speaker 1>to digest dairy and people of African American, Hispanic, and

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<v Speaker 1>or Native American descent are not. Northern Europeans, especially Scandinavians,

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<v Speaker 1>tend to hang onto the lactaste gene. Folks from Southern

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<v Speaker 1>Europe are split about fifty fifty, but a full ent

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<v Speaker 1>of Asians are lactose intolerant, hence the absence of dairy

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<v Speaker 1>in many traditional foods from around the continent. Parts of Africa,

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<v Speaker 1>with the history of cattle farming have populations with as

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<v Speaker 1>much as lactaste persistence. Scientists aren't sure why some people

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<v Speaker 1>lose the lactaste gene, but they have figured out that

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<v Speaker 1>the genetic mutation appeared about seven thousand, five hundred years

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<v Speaker 1>ago among dairy farming populations in Central Europe and eastern Africa.

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<v Speaker 1>The theory is that the mutation was random, as all

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<v Speaker 1>mutations are, but it became genetically advantageous in these dairy

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<v Speaker 1>eating populations and thus spread rapid lee. To this day,

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<v Speaker 1>there are still high rates of lactea persistence in those areas.

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<v Speaker 1>Lactase persistence might not be a necessity for survival in

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<v Speaker 1>the modern world, but it does make life more pleasurable

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<v Speaker 1>for many people. So if you can enjoy ice cream, Sundays, milkshakes,

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<v Speaker 1>and pizza with no problem. Remember that you're one of

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<v Speaker 1>the lucky ones. Today's episode was written by Alison Cooper

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<v Speaker 1>and produced by Tyler Klang. Brain Stuff is production of

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<v Speaker 1>I Heart Radio's How Stuff Works. For more on this

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<v Speaker 1>and lots of other topics, visit our home planet, how

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