Lactose1Are you a milk drinker?  I had always thought it a bit strange that my husband like a big glass of milk with dinner.  It just didn’t appeal to me at all. I didn’t think ever think about lactose intolerance, though, because I still put milk in coffee and on cereal. Turns out that I am one of those who doesn’t produce lactase as an adult…

Getting into the science:
Lactose, a sugar in milk, is broken down by the enzyme lactase which our bodies produce in the small intestines.  For some people, the production of the lactase enzyme stops when they become an adult, driven by a genetic variation near the LCT gene.  This means that some adults are genetically predisposed to not be able to consume larger quantities of milk.  (This is just one way, not the only way, that people become lactose intolerant.)


The percentage of the population with the genetic variations differs quite a bit among people with different backgrounds.  Producing lactase as an adult is the most common genotype for Caucasian populations, while in Asian populations, the majority do not produce lactase as an adult.

For Caucasians, the main polymorphism to look at is rs4988235.

Check your 23andMe results for rs4988235 – LCT gene:
AA: Still produces lactase as an adult
AG: Still produces lactase as an adult (probably less than those with AA – study)
GG: No longer produces lactase as an adult

If your genotype is GG on rs4988235, you will not produce lactase and will probably not be able to handle larger quantities of milk as an adult. From talking with other people about this, it seems that those with GG naturally limit their intake of milk and are probably not pouring themselves a glass of milk every night at dinner.  Bacteria in the gut can also help break down lactose, so even those who don’t produce lactase can often handle some amount of milk.

Interestingly, a Dutch study showed that while the GG genotype resulted in adults having a lower dietary calcium intake, that did not correspond to a lower bone density or more fractures.

For those of African origin, a different polymorphism found in the MCM6 gene is found in about 10-15% of the population and associated with being able to produce lactase as an adult.  Other polymorphisms also exist that aren’t covered by 23andMe.

Check your 23andMe results for rs41380347 — MCM6 gene:
C: Still produces lactase as an adult [study]
AC: Still produces lactase as an adult
AA: No longer produces lactase as an adult


Probiotics to the rescue?

Quite a few studies have looked at the effect of probiotics on lactose intolerance.  One study from May 2016 found that a specific strain of Lactobacillus acidophilus was significantly effective in reducing the symptoms of lactose intolerance.  There are many types of lactobacillus bacteria available as probiotics and in yogurt or other fermented foods.  It is likely that some strains will be much more effective than others in reducing lactose intolerance symptoms for an individual, and it may be worthwhile to try several different types of Lactobacillus probiotics.

If you are interested in digging deeper into the types and numbers of lactose-consuming bacteria in your gut, you could do a microbiome sample from uBiome (referrer link – get 15% off!).

More to read:

originally published 2/23/15, updated 10/17

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