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This week we are going to be looking at a gene that affects how well we can tolerate lactose. Roughly 65% of the world’s population lose the ability to digest lactose, the sugar found in milk, after weaning. From an evolutionary perspective, this makes sense – humans typically need to digest milk when they are babies because their main source of nutrition is breast milk; however, once the child has stopped breast feeding, historically there was no need for them to continue to digest lactose, because milk wasn’t readily available. However, as humans migrated out of Africa into Asia, and eventually into Europe, a small polymorphism occurred which enabled some of them to continue to digest lactose into adulthood.

This week we are going to be looking at a gene that affects how well we can tolerate lactose. Roughly 65% of the world’s population lose the ability to digest lactose, the sugar found in milk, after weaning. From an evolutionary perspective, this makes sense – humans typically need to digest milk when they are babies because their main source of nutrition is breast milk; however, once the child has stopped breast feeding, historically there was no need for them to continue to digest lactose, because milk wasn’t readily available. However, as humans migrated out of Africa into Asia, and eventually into Europe, a small polymorphism occurred which enabled some of them to continue to digest lactose into adulthood. This was useful because it now meant that instead of killing their animals for meat, they could consume their milk, thus creating a renewable source of nutrition. This, in turn, allowed humans to migrate even longer distances, spreading into Northern Europe. Today, between 85-95% of Britons are lactose tolerant, compared with around 60-75% of Southern Europeans. The number of lactose tolerant individuals gets smaller as we move into Asia and Africa; in some places 100% of the population are lactose intolerant.

 

Lactose intolerance occurs when the body is unable to digest lactose, the sugar found in milk. Instead of being absorbed through the small intestine, the undigested lactose travels to the colon, where bacteria begin to break it down via fermentation. This process creates a lot of gas, which leads to the symptoms associated with lactose intolerance – bloating, stomach cramps, excessive gas, and diarrhoea. The main cause of lactose intolerance is called primary lactose intolerance; this is where the body doesn’t produce lactase, the enzyme that breaks down lactose. This is genetic, and determined by the LCT SNP C/T(-13910.

 

The LCT SNP has two alleles, C & T; the T allele is what gives people the ability to continue to produce lactase, the enzyme which digests lactose, into adulthood. The table below summarises the different genotypes:

 

LCT Genotype

Effect on Lactose Tolerance

Dietary Recommendations

CC

Likely lactose intolerant

Should likely avoid milk-based products, at least in high amounts.

CT/TT

Lactose tolerant

Should be fine to consume milk and milk products.

 

In summary then, if you have a T allele, you have the ability to produce lactase, which means you should be able to tolerate milk products. Those without a T allele will likely have lost the ability to produce lactase, and as such will be unlikely to tolerate milk products. However, it’s worth pointing out that having at least one T allele doesn’t guarantee that you can tolerate milk products; this is because some people might have something called secondary lactose intolerance, which is not genetic, and is instead often caused by a bacterial infection, virus, or stomach injury/disease (such as coeliac disease). It’s also possible to be lactose tolerant, but have a cow’s milk protein allergy – although this affects less than 1% of people. The flipside of this is that even people with lactose intolerance can often consume small amounts of lactose without any symptoms. Nevertheless, knowing and understanding your LCT genotype can be important when it comes to seeing which foods you can tolerate, and explaining why you might experience certain symptoms with milk products.

Tags:

Gene In Focus Genetics DNAFit LCT Lactose Intolerance Lactose Diet Nutrition

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