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milk products digestion

Lactose intolerence

Many adults lose the ability to digest lactose, up to a stage were intake of dairy products is accompanied by abdominal cramps, bloating, flatulence and diarrhea.


The lactase enzyme is responsible for lactose metabolism. Genetic variations in genes regulating its production determine how well can you digest milk products.

Lactose intolerance (aka lactase non-persistence) is a condition of reduced ability to digest lactose, due to a relative low levels of the lactase enzyme in the small intestine.

Lactose is a sugar found in milk, and cannot be absorbed intact. The lactase enzyme breaks it down into glucose and galactose, which the body can utilize. When lactase enzyme levels are low, bacteria in the digestive system ferment the lactose, which produces gases and cause discomforts.


Lactase levels are high in babies and young children, allowing the intake of their mother’s milk. In many populations, lactase levels drop in adulthood and individuals tend to lose the ability to digest milk. However, in some ethnic groups (see figure), majority of individuals are lactose persistent, preserving the infantile ability that allows digestion of milk. Yet, lactose intolerance is quite a common condition even in these groups.

Prevalence of lactose persistence in ethnic groups, according to their geographical origins in the old world:

Most people of Middle Eastern and Caucasian origin tend to be lactose persistent (50-90%), while only 10%-20% are lactose persistent among people from South-East Asia. Some studies estimate lactose intolerance as high as 99% of the total Chinese population.

Genomic coordinates (GRCh38): 2:135,839,625-135,876,476

While LCT is the gene that encodes for the lactase enzyme, variations in the the MCM6 gene have the biggest effect on lactase levels in the digestive tract, and our ability to digest milk products. MCM6 serves as a regulator gene on the LCT gene activity levels. 

Lactose intolerant individuals who consume lactose-containing dairy products may experience abdominal pain, bloating, flatulence, nausea, and diarrhea beginning 30 minutes to 2 hours later.

However, most lactose intolerant individuals retain some lactase activity and can include varying amounts of lactose in their diets without experiencing symptoms. Often, affected individuals have difficulty digesting fresh milk but can eat certain dairy products such as cheese or yogurt without discomfort. These foods are made using fermentation processes that break down much of the lactose in milk.

















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