WEBVTT - Are Humans Built to Drink Milk After Childhood? 0:00:01.960 --> 0:00:07.160 Welcome to brain stuff production of iHeartRadio. Hey, brain stuff, 0:00:07.200 --> 0:00:11.520 laurin vogel bomb here. When people can't digest milk, we 0:00:11.560 --> 0:00:15.960 call that lactose intolerance. This might seem to signify that 0:00:16.000 --> 0:00:19.800 it's an unusual condition that most people are just fine 0:00:19.880 --> 0:00:23.840 consuming dairy products like milk, cheese, and ice cream, But 0:00:23.920 --> 0:00:27.480 it turns out that we pour souls who get gassy, crampy, 0:00:27.560 --> 0:00:31.880 and otherwise digestively miserable after eating dairy products are actually 0:00:31.920 --> 0:00:35.360 in the majority worldwide. It's the people who can handle 0:00:35.400 --> 0:00:39.520 milk where the weird ones. A. Lactose is the main 0:00:39.560 --> 0:00:42.559 sugar in all mammal milk, and everyone is born with 0:00:42.560 --> 0:00:45.600 the gene that codes for producing lactase, which is the 0:00:45.680 --> 0:00:49.479 enzyme in our bodies that processes lactose, so when we're babies, 0:00:49.600 --> 0:00:52.960 we all have the ability to digest milk. The human 0:00:53.000 --> 0:00:56.440 body produces lactase in the small intestine, where it breaks 0:00:56.440 --> 0:01:00.200 down lactose into glucose and glactose, which are bodies can 0:01:00.240 --> 0:01:04.640 easily absorb into our bloodstream, But for reasons unknown, the 0:01:04.720 --> 0:01:07.440 gene for lactase tends to shut off at about the 0:01:07.480 --> 0:01:09.240 time that most of us would be weaned off of 0:01:09.280 --> 0:01:13.280 breast milk and onto solid foods. Most people's bodies don't 0:01:13.319 --> 0:01:15.920 create any lactase, or very little of it by the 0:01:15.920 --> 0:01:19.160 time they're five years old or so. In the absence 0:01:19.160 --> 0:01:22.040 of lactase, the excess sugar sitting around in your small 0:01:22.040 --> 0:01:25.080 intestines causes your body to try to flush it out 0:01:25.400 --> 0:01:29.280 by secreting fluids and moving things along faster than normal. 0:01:30.400 --> 0:01:33.400 By the time the lactose reaches your colon, the mostly 0:01:33.440 --> 0:01:38.399 helpful microorganisms there eat it and poop things like carbon dioxide, hydrogen, 0:01:38.520 --> 0:01:42.960 and methane. In combination. This can lead to those unpleasant 0:01:42.959 --> 0:01:48.600 symptoms of diarrhea, gas, and cramps. Some lucky people, however, 0:01:48.800 --> 0:01:51.800 carry a genetic mutation that allows the lactase gene to 0:01:51.960 --> 0:01:55.400 keep working. Sometimes it continues for just a few more years, 0:01:55.640 --> 0:01:59.480 sometimes for a lifetime. Up to ninety percent of Americans 0:01:59.520 --> 0:02:02.440 have a functional lactase gene, so in the US it's 0:02:02.440 --> 0:02:06.440 a little unusual to be lactose intolerant. About worldwide, more 0:02:06.480 --> 0:02:09.760 than sixty percent of people lose the ability to process lactose. 0:02:10.320 --> 0:02:13.840 Because lactose intolerance is the more common condition around the globe, 0:02:14.120 --> 0:02:16.919 scientists and researchers in the field actually use the term 0:02:17.080 --> 0:02:20.399 lactase persistence for the rarer case of people who can 0:02:20.480 --> 0:02:23.960 digest dairy. Because the function of the gene is genetic, 0:02:24.400 --> 0:02:27.919 certain populations are more prone to lactase persistence than others. 0:02:28.800 --> 0:02:32.000 Northern Europeans, especially Scandinavians, tend to hang on to a 0:02:32.040 --> 0:02:35.640 functional lactase gene, along with some populations from West Africa, 0:02:35.840 --> 0:02:39.799 East Africa, and the Middle East. People from Southern Europe, 0:02:39.840 --> 0:02:42.720 the rest of Africa, much of the Americas, Central Asia, 0:02:42.800 --> 0:02:45.960 and Northern Asia are less likely to have tolerance, and 0:02:46.240 --> 0:02:50.600 it's super rare in Southeastern Asia. Based on these patterns 0:02:50.639 --> 0:02:53.640 and non genetic research, it seems that the mutations that 0:02:53.720 --> 0:02:58.000 code for keeping the lactase gene active appeared about seven thousand, 0:02:58.080 --> 0:03:01.560 five hundred years ago among cattle farming populations in Central 0:03:01.560 --> 0:03:04.600 Europe and Eastern Africa, and in camel herders in the 0:03:04.639 --> 0:03:08.520 Middle East. The theory is that the mutation was random, 0:03:08.639 --> 0:03:12.880 as all mutations are, but it became genetically advantageous in 0:03:13.000 --> 0:03:17.720 these dairy eating populations and thus spread rapidly. To this day, 0:03:17.760 --> 0:03:20.560 there are still high rates of lactase persistence in these areas. 0:03:21.520 --> 0:03:24.679 Lactase persistence might not be a necessity for survival in 0:03:24.720 --> 0:03:27.600 the modern world, but it can make life easier and 0:03:27.760 --> 0:03:33.440 perhaps more delicious. So if you can enjoy conventional ice cream, Sundays, milkshakes, 0:03:33.440 --> 0:03:36.240 and pizza with no problem, remember that you're one of 0:03:36.240 --> 0:03:39.120 the lucky ones. If you're not, remember that there are 0:03:39.160 --> 0:03:47.400 lots of dairy alternatives out there. Today's episode is based 0:03:47.400 --> 0:03:49.880 on the article are humans built to drink milk as adults? 0:03:49.960 --> 0:03:52.880 On How stuffworks dot Com? Written by Alison Cooper. Rain 0:03:52.920 --> 0:03:54.920 Stuff is production of by Heart Radio in partnership with 0:03:54.960 --> 0:03:57.200 how stuffworks dot Com, and is produced by Tyler Klang. 0:03:57.760 --> 0:04:00.200 For more podcasts from My heart Radio, visit the heart 0:04:00.240 --> 0:04:02.920 Radio app, Apple Podcasts, or wherever you listen to your 0:04:02.920 --> 0:04:03.640 favorite shows.