1 00:00:01,920 --> 00:00:07,040 Speaker 1: Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff, 2 00:00:07,120 --> 00:00:11,160 Speaker 1: Lauren Bogle Bomb here. When people can't digest milk, we 3 00:00:11,240 --> 00:00:14,880 Speaker 1: call them lactose intolerant. This seems to signify that it's 4 00:00:14,880 --> 00:00:18,200 Speaker 1: an unusual condition, that most people are just fine with milk, 5 00:00:18,280 --> 00:00:21,400 Speaker 1: cheese and ice cream, and that lactose intolerance is something 6 00:00:21,440 --> 00:00:24,640 Speaker 1: that needs to be fixed or helped. But it turns 7 00:00:24,640 --> 00:00:27,600 Speaker 1: out that those poor souls who get gassy, crampy, and 8 00:00:27,760 --> 00:00:31,680 Speaker 1: otherwise digestively miserable after eating dairy products are actually in 9 00:00:31,720 --> 00:00:34,640 Speaker 1: the majority worldwide. It's the people who can handle milk 10 00:00:34,640 --> 00:00:38,120 Speaker 1: who are the weird ones. Lactose is the main form 11 00:00:38,159 --> 00:00:41,600 Speaker 1: of sugar in all mammal milk, and everyone is born 12 00:00:41,680 --> 00:00:44,320 Speaker 1: with the gene that codes for the creation of lac taste, 13 00:00:44,560 --> 00:00:48,640 Speaker 1: which is the enzyme that processes lactose. When we're babies, 14 00:00:48,640 --> 00:00:51,440 Speaker 1: in other words, we all have the ability to digest milk. 15 00:00:52,120 --> 00:00:55,600 Speaker 1: The small intestine produces lac taste. It breaks down lactose 16 00:00:55,640 --> 00:00:58,800 Speaker 1: into glucose and galactose, which can be easily absorbed into 17 00:00:58,840 --> 00:01:03,000 Speaker 1: the bloodstream. But for reasons unknown, the lactaste gene tends 18 00:01:03,040 --> 00:01:05,440 Speaker 1: to shut off about the time we're weaned from breast milk. 19 00:01:06,080 --> 00:01:09,000 Speaker 1: Most people don't create any lactaste, or very little of 20 00:01:09,040 --> 00:01:11,000 Speaker 1: it by the time they're five years old or so. 21 00:01:11,840 --> 00:01:15,319 Speaker 1: In the absence of lactaste, undigested lactose just sits in 22 00:01:15,360 --> 00:01:20,280 Speaker 1: the colon and ferments, causing all kinds of uncomfortable side effects. Basically, 23 00:01:20,520 --> 00:01:23,360 Speaker 1: your gut bacteria eat it and they excrete gas and 24 00:01:23,400 --> 00:01:28,720 Speaker 1: other wastes, which you then have to excrete. Some people, however, 25 00:01:28,800 --> 00:01:31,679 Speaker 1: carry a genetic mutation that allows the lactaste gene to 26 00:01:31,760 --> 00:01:35,360 Speaker 1: keep working. Sometimes it continues for just a few more years, 27 00:01:35,400 --> 00:01:40,200 Speaker 1: sometimes for a lifetime. Of Americans have a functional lactaste gene, 28 00:01:40,520 --> 00:01:43,080 Speaker 1: so in the United States it is unusual to be 29 00:01:43,200 --> 00:01:47,640 Speaker 1: lactose intolerant, but worldwide, more than six people lose the 30 00:01:47,680 --> 00:01:51,800 Speaker 1: ability to process lactose. Because lactose intolerance is the more 31 00:01:51,800 --> 00:01:54,800 Speaker 1: common condition around the globe, scientists and researchers in the 32 00:01:54,840 --> 00:01:58,240 Speaker 1: field actually use the term lac taste persistence for people 33 00:01:58,240 --> 00:02:02,720 Speaker 1: who can digest milk. Certain populations are more prone to 34 00:02:02,800 --> 00:02:06,120 Speaker 1: lac taste persistence than others. In the United States, people 35 00:02:06,160 --> 00:02:08,519 Speaker 1: of Caucasian descent are much more likely to be able 36 00:02:08,560 --> 00:02:12,120 Speaker 1: to digest dairy and people of African American, Hispanic, and 37 00:02:12,320 --> 00:02:17,239 Speaker 1: or Native American descent are not. Northern Europeans, especially Scandinavians, 38 00:02:17,440 --> 00:02:20,720 Speaker 1: tend to hang onto the lactaste gene. Folks from Southern 39 00:02:20,800 --> 00:02:25,040 Speaker 1: Europe are split about fifty fifty, but a full ent 40 00:02:25,120 --> 00:02:28,680 Speaker 1: of Asians are lactose intolerant, hence the absence of dairy 41 00:02:28,720 --> 00:02:32,440 Speaker 1: in many traditional foods from around the continent. Parts of Africa, 42 00:02:32,480 --> 00:02:34,640 Speaker 1: with the history of cattle farming have populations with as 43 00:02:34,720 --> 00:02:40,400 Speaker 1: much as lactaste persistence. Scientists aren't sure why some people 44 00:02:40,440 --> 00:02:43,040 Speaker 1: lose the lactaste gene, but they have figured out that 45 00:02:43,080 --> 00:02:45,919 Speaker 1: the genetic mutation appeared about seven thousand, five hundred years 46 00:02:45,919 --> 00:02:50,160 Speaker 1: ago among dairy farming populations in Central Europe and eastern Africa. 47 00:02:51,040 --> 00:02:53,320 Speaker 1: The theory is that the mutation was random, as all 48 00:02:53,440 --> 00:02:57,440 Speaker 1: mutations are, but it became genetically advantageous in these dairy 49 00:02:57,480 --> 00:03:01,560 Speaker 1: eating populations and thus spread rapid lee. To this day, 50 00:03:01,600 --> 00:03:04,520 Speaker 1: there are still high rates of lactea persistence in those areas. 51 00:03:05,960 --> 00:03:08,760 Speaker 1: Lactase persistence might not be a necessity for survival in 52 00:03:08,800 --> 00:03:11,720 Speaker 1: the modern world, but it does make life more pleasurable 53 00:03:11,760 --> 00:03:15,840 Speaker 1: for many people. So if you can enjoy ice cream, Sundays, milkshakes, 54 00:03:15,880 --> 00:03:18,440 Speaker 1: and pizza with no problem. Remember that you're one of 55 00:03:18,480 --> 00:03:26,160 Speaker 1: the lucky ones. Today's episode was written by Alison Cooper 56 00:03:26,200 --> 00:03:28,760 Speaker 1: and produced by Tyler Klang. Brain Stuff is production of 57 00:03:28,800 --> 00:03:30,920 Speaker 1: I Heart Radio's How Stuff Works. For more on this 58 00:03:31,000 --> 00:03:32,960 Speaker 1: and lots of other topics, visit our home planet, how 59 00:03:33,000 --> 00:03:35,600 Speaker 1: stuff Works dot com. And for more podcasts for my 60 00:03:35,640 --> 00:03:38,720 Speaker 1: heart Radio, visit the iHeart Radio app, Apple Podcasts, or 61 00:03:38,760 --> 00:03:40,400 Speaker 1: wherever you listen to your favorite shows.