The Genes Behind Lactose Intolerance

Written by Yun Jun Ooi
Posted on July 16, 2019

Malaysians have such a strong coffee-drinking culture, which is a stark contrast to our milk-drinking culture. Let’s explore lactose intolerance and what you could do it you are lactose intolerant.

What is Lactose Intolerance?

Lactose is a type of carbohydrate, which is present in milk or any dairy products. It is normally broken down by the enzyme lactase, into glucose and galactose, which can be absorbed by our body.

But when your body produces less lactase, lactose doesn’t get digested, which can cause gastrointestinal complications. This is known as lactose intolerance.

But do you know that, even though you have low level of lactase in your body, you may still be able to digest lactose normally and not be considered as lactose intolerant? Lactose intolerant individuals are those with low lactase levels which causes symptoms after their dairy consumption.

What genes cause Lactose Intolerance?

LCT gene gives instructions to our body to produce lactase.

The occurrence of lactose intolerance in most of the infants is due to the mutations in the LCT gene. Low lactase production will lead to severely impaired ability to digest lactose in breast milk or formula.

While for adults, the occurrence of lactose intolerance is due to the decreasing activity of the LCT gene. The LCT gene expression is controlled by a DNA sequence called a regulatory element, located within a nearby gene called MCM6. By having a different expression of MCM6 gene, it may impact the LCT gene expression, leading to the occurrence of LI.

What is the mechanism behind it?

Normally, when we consume dairy product, lactase in our small intestine, will break down the lactose and our body will absorb it. But in individuals with lactose intolerance, the lactose is not broken down.

Instead, it will continue traveling in the digestive system to the colon where good bugs present, known as gut microbiota. The microbiota will ferment the lactose and produce gases like hydrogen and carbon dioxide, which causes bloating and diarrheoa.

How many types are there?

Among all the Malaysians there are about 80-100% of them who are lactose intolerance, according to the survey by Food Intolerance Network.

There are 4 different types of lactose intolerance (LI) which are present nowadays:

  • Primary LI
  • Secondary LI
  • Developmental LI
  • Congenital LI

Primary LI

This is the most common LI present among Malaysians. It happens due to the reduction of lactase production in an person’s body by about the age of 5. The reduction of lactase production increases the difficulty of the digestion of dairy products.

Secondary LI

Secondary LI occurs due to the physical impacts on the small intestines. For example, injury, illnesses or even surgery. When the small intestine is affected, it may cause a reduction in lactase production. Here are a few examples of diseases which are linked to low lactase production, such as Celiac disease, Crohn’s disease.

Developmental LI

For pre-matured babies, they may be born with developmental LI. They have insufficient intestinal lactase due to the incomplete development of their small intestine. It only lasts for a short while after birth. Once the body starts to develop, the baby will have a complete development of enzymes.

Congenital LI

Congenital LI is the rarest type of LI. An individual with congenital LI has no lactase (or very low amount of lactase) produced by the small intestines since birth. It is a genetic disorder where 2 autosomal recessive genes are received from the parents. This form of LI results in severe diarrheoa acidosis as well as hypercalcaemia.

What should you do if you have lactose intolerance?

If I am lactose intolerant, does it mean that I can’t consume any dairy product?

The answer is No. There are some replacement products available for LI individuals. For example, lactose-free or lactose-reduced milk, and ice cream can be found in the supermarket.

Furthermore, you can also consume supplements, like Lactaid (an enzyme which helps you in breaking down milk sugar) if you still want to consume the real dairy product.

Besides drinking milk, you can also consume other food sources which contain high amount of calcium and vitamin D to substitute with the dairy product. For example, almonds, fatty fish, tofu, kale, soy milk, and others.

Do note that there is no way to boost your body’s production of lactase, but you can do something to avoid the discomfort caused due to lactose intolerance.


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