system
Given the following post, respond as if you're commenting on Reddit:
human
What causes lactose intolerance?  Can someone 
lactose intolerant become tolerant over time?

Someone told me that the reason more Asians are lactose intolerant is due to the food culture.   Babies are born with tolerance due to the bacteria in their gut, but once they are weaned off breastmilk or formula, they no longer consume dairy products, since most Asians do not drink cow's milk or eat cheese.  This will lead to the lactose dependent bacteria in the gut to die off, rendering the person unable to digest lactose properly.  Is this true?

Is there a way to reverse the process?  Maybe ingest cultures of lactose-eating bacteria?
gpt
The ability to metabolize lactose is dependent on a protein called lactase. Those who have decreased levels of lactase or non-functional versions would be unable to digest lactose, so lactose would instead be "digested" by bacteria in the gut, which would then produce gas in the form of methane. This explains the symptoms of lactose intolerance - bloating, loose stools and flatulence.

The activity and presence of lactase varies significantly throughout your life. Most infants have the ability to digest lactose, but this activity decreases as you age. The great majority of the world adult population is unable to digest lactose in great quantities - such as that found in milk - with the exception of populations from Northern European origin, where presumably high levels of lactase activity evolved to allow milk drinking late into adulthood.

It is unlikely that one can regain tolerance as it has to do with decreased presence of a cellular enzyme.  People with lactose intolerance can take Lactaid, which provides exogenous lactase, to allow digestion and avoidance of symptoms.