Thank Your Ancestors For Your Ability to Drink Milk

Niha Zubair, Arivale Clinical Research Scientist, PhD
Niha Zubair
Arivale Clinical Research Scientist, PhD

Are we supposed to drink milk? Of course, as infants, yes. But, as adults? Across the wellness space, you’ll run into headlines arguing both ways.

The “no” camp makes some good points. Humans are the only mammal species that continues to drink milk into adulthood, and roughly two-thirds of adults worldwide experience symptoms of lactose intolerance. The “yes” camp will argue that while most humans do lose the ability to digest milk, there are still many adults who can drink it without problems. For those people, milk can be a solid source of calcium, vitamin D, and protein. So … got milk?

Let’s save arguments on the nutritional importance of milk for a later day. The real question isn’t whether or not humans should drink milk, but rather, can you? And to answer that question, we have to look at your ancestry.

How Lactose Intolerance Works

Before we delve into the details of ancestry and drinking milk, it’s important to understand what causes lactose intolerance.

For your gut to digest lactose—the kind of sugar found in milk—it needs an enzyme called lactase, and the LCT gene gives your body the instructions to make it. But, as you age, your LCT gene gets turned “off.” When this happens, lactose no longer gets absorbed into your blood stream, but rather goes directly to your colon undigested. Here, it reacts with your gut bacteria to create all kinds of unpleasant symptoms—bloating, gas, upset stomach, diarrhea, the works. In other words, lactose intolerance.

But for some people, this never happens.

As humans evolved as a species, certain populations developed what’s known as lactase persistence. Due to some genetic changes near the LCT gene, people gained the ability to keep their LCT gene turned “on” so they could keep making that lactase.

Ancestry and Lactose Intolerance

Lactase persistence is most common in populations that domesticated cattle. It’s not surprising these groups evolved to develop a tolerance. For them, milk was a rich source of energy. And while there are many alternative ways today to get the nutritional benefits ancient populations found in milk, this inherited tolerance is still present in many people’s DNA.

It’s long been known genetics impact lactose intolerance, but most genetic tests just focus on one variant that’s most common in people of Northern European and Indian descent. This is problematic, as many populations developed the ability to digest milk over time. Several other variants near the LCT gene—common in people of East African, South African, and Middle Eastern descent—can also lead to lactase persistence and should be tested for accurate results.

Arivale currently looks at four variants associated with lactase persistence. If you’re an Arivale Member, you can find them in the Optimal Nutrition section of your dashboard. Scientists acknowledge there could still be more undiscovered variants that lead to lactase persistence.

The Gut Microbiome Curveball

Interestingly, some people who have the genetics associated with lactose intolerance still can digest milk without problems. Depending on your gut microbiome composition, it is possible that the bacteria in your gut can break down undigested lactosekeeping the symptoms of intolerance at bay.

Here’s where it gets even more interesting. For those people, it’s especially important to keep consuming dairy products, as going dairy-free for a period could alter their gut composition and create symptoms of intolerance if they decide to reintroduce dairy into their diet.

On the other hand, some people with the genetic ability to digest lactose do have intolerance symptoms. It could be because their small intestine was physically injured after an illness, surgery, or by medication, resulting in a decrease in lactase production.1-4

These exceptions are a good reminder that our genes aren’t our destiny. But they can give us some fascinating clues into both our health and ancestry.




  1. Kosnai I, Kuitunen P, Savilahti E, Rapola J, Köhegyi J. Cell kinetics in the jejunal crypt epithelium in malabsorption syndrome with cow’s milk protein intolerance and in coeliac disease of childhood. Gut. 1980 Dec;21(12):1041-6.
  2. Ulshen MH, Rollo JL. Pathogenesis of escherichia coli gastroenteritis in man–another mechanism. N Engl J Med. 1980 Jan 10;302(2):99-101.
  3. Carrera E, Nesheim MC, Crompton DW. Lactose maldigestion in Ascaris-infected preschool children. Am J Clin Nutr. 1984 Feb;39(2):255-64.
  4. Brunser O, Castillo C, Araya M. Fine structure of the small intestinal mucosa in infantile marasmic malnutrition. Gastroenterology. 1976 Apr;70(4):495-507.