Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff, Lauren Bogle Bomb here. When people can't digest milk, we call them lactose intolerant. This seems to signify that it's an unusual condition, that most people are just fine with milk, cheese and ice cream, and that lactose intolerance is something that needs to be fixed or helped. But it turns out that those poor souls who get gassy, crampy, and otherwise digestively miserable after eating dairy products are actually in
the majority worldwide. It's the people who can handle milk who are the weird ones. Lactose is the main form of sugar in all mammal milk, and everyone is born with the gene that codes for the creation of lac taste, which is the enzyme that processes lactose. When we're babies, in other words, we all have the ability to digest milk. The small intestine produces lac taste. It breaks down lactose into glucose and galactose, which can be easily absorbed into
the bloodstream. But for reasons unknown, the lactaste gene tends to shut off about the time we're weaned from breast milk. Most people don't create any lactaste, or very little of it by the time they're five years old or so. In the absence of lactaste, undigested lactose just sits in the colon and ferments, causing all kinds of uncomfortable side effects. Basically, your gut bacteria eat it and they excrete gas and
other wastes, which you then have to excrete. Some people, however, carry a genetic mutation that allows the lactaste gene to keep working. Sometimes it continues for just a few more years, sometimes for a lifetime. Of Americans have a functional lactaste gene, so in the United States it is unusual to be lactose intolerant, but worldwide, more than six people lose the
ability to process lactose. Because lactose intolerance is the more common condition around the globe, scientists and researchers in the field actually use the term lac taste persistence for people who can digest milk. Certain populations are more prone to lac taste persistence than others. In the United States, people of Caucasian descent are much more likely to be able to digest dairy and people of African American, Hispanic, and
or Native American descent are not. Northern Europeans, especially Scandinavians, tend to hang onto the lactaste gene. Folks from Southern Europe are split about fifty fifty, but a full ent of Asians are lactose intolerant, hence the absence of dairy in many traditional foods from around the continent. Parts of Africa, with the history of cattle farming have populations with as
much as lactaste persistence. Scientists aren't sure why some people lose the lactaste gene, but they have figured out that the genetic mutation appeared about seven thousand, five hundred years ago among dairy farming populations in Central Europe and eastern Africa. The theory is that the mutation was random, as all mutations are, but it became genetically advantageous in these dairy
eating populations and thus spread rapid lee. To this day, there are still high rates of lactea persistence in those areas. Lactase persistence might not be a necessity for survival in the modern world, but it does make life more pleasurable for many people. So if you can enjoy ice cream, Sundays, milkshakes, and pizza with no problem. Remember that you're one of the lucky ones. Today's episode was written by Alison Cooper and produced by Tyler Klang. Brain Stuff is production of
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