Lactose Intolerance Genes

Key takeaways:
~ Your genes control whether you will likely produce lactase as an adult.
~ It’s easy to check your 23 and Me raw data to see if you are likely lactose intolerant.
~ Even if you don’t produce lactase, your gut bacteria make it possible to break down some dairy.

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Lactose and Lactase:

Lactose, a sugar in milk, is broken down by lactase, an enzyme produced in the small intestines. This is how babies can digest breast milk.

While essential for babies and children to be able to break down lactose, for many people, the production of the lactase enzyme stops before adulthood.

Whether or not you still produce lactase as an adult is based on your genes. A genetic variation near the LCT gene drives the persistence of lactase.

Thus, many adults are genetically predisposed not to be able to digest larger quantities of milk, also known as lactose intolerance. Others may be able to consume all the dairy that they wish to with no digestive problems.

Personally, I had always thought it a bit strange when people drink a big glass of milk with dinner. It just didn’t appeal to me…. yuck. I never thought about lactose intolerance, though, because I still drink small amounts of milk in my coffee and cereal. It turns out that I am one of those people who doesn’t produce lactase as an adult. I rely on bacteria in my gut to break down lactose, so I naturally steer away from drinking a lot of milk at once.

What exactly is lactose?

Lactose is a compound sugar, meaning it is two different sugar molecules stuck together. Glucose and galactose make up lactose. The lactase enzyme splits apart the sugar molecule, and your cells then use the glucose and galactose for energy.

Without lactase to split up lactose, it ends up traveling through your intestines and feeding your gut microbes. An overabundance of lactose can disrupt your microbial balance – giving you bloating, cramping, and even diarrhea.

Lactose intolerance: Asian vs. European Ancestry

The percentage of the population with genetic variations differs quite a bit among people with different backgrounds.

  • Producing lactase as an adult is the most common genotype for European Caucasian populations (90%+ can digest lactose).
  • In Asian populations, the vast majority (~99%) do not produce lactase as an adult.

A theory for this occurrence seems to be an adaptation by Caucasian populations in Europe who relied on dairy products as a source of protein. Those born with the LCT variant could thrive on the higher protein afforded by dairy products. This made it a survival advantage to digest dairy in areas where sheep and cattle were used for milk.

For people with European Caucasian ancestry, the main variant to look at is rs4988235. It is located in the MCM6 gene, which influences the LCT gene. Approximately 90% of Caucasians will have A/A or A/G and still produce lactase to break down milk as an adult. In Asian ancestry, less than one percent will carry the G allele.

People with African ancestry may find that they carry a different variant (rs145946881) in the MCM6 gene that also causes lactase persistence as an adult.

Bacteria in the gut can also break down lactose, so even those who don’t produce lactase can often handle digesting limited amounts of milk.

Lactose Intolerance Genotype Report


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Check your genetic data for rs4988235 (23andMe v4, v5; AncestryDNA):

  • A/A: Still produces lactase as an adult
  • A/G: Still produces lactase as an adult, but less than those with A/A[ref]
  • G/G: No longer produces lactase as an adult

Members: Your genotype for rs4988235 is .


For people of African ancestry, a different variant of the MCM6 gene occurs in about 10-25% of the population and is associated with being able to produce lactase as an adult.

Check your genetic data for rs145946881 (AncestryDNA):

  • C/C: Still produces lactase as an adult[ref]
  • A/C: Still produces lactase as an adult
  • A/A: No longer produces lactase as an adult

Members: Your genotype for rs145946881 is .


Rare mutations: A very small number of people may also have a rare mutation (not covered by 23andMe or AncestryDNA) that causes the lactase gene not to function at all, even in childhood.

Lifehacks for Lactose Intolerance

Navigating Foods High in Lactose:[ref]
The foods highest in lactose are dairy products:

  • Milk and buttermilk contain about 12 g/cup.
  • A cup of evaporated milk contains about 25 g of lactose.
  • Ice cream varies by brand, because some brands add in extra lactose.

Butter and cream contain virtually no lactose, and hard cheeses are usually pretty low in lactose as well.

Yogurt does contain lactose, but it also contains Lactobacillus bacteria that can break down the lactose. Many people with lactose intolerance do fine with yogurt in moderate amounts.

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Probiotics to the rescue!

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About the Author:
Debbie Moon is the founder of Genetic Lifehacks. Fascinated by the connections between genes, diet, and health, her goal is to help you understand how to apply genetics to your diet and lifestyle decisions. Debbie has a BS in engineering and also an MSc in biological sciences from Clemson University. Debbie combines an engineering mindset with a biological systems approach to help you understand how genetic differences impact your optimal health.

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