Why Do People in Asia Often Experience Stomach Pain After Drinking Milk?

Lactose intolerance affects a significant portion of the global adult population, with estimates suggesting 68-70% struggle to digest lactose, the natural sugar in milk and dairy products. This digestive disorder can lead to uncomfortable symptoms such as bloating, diarrhea, abdominal pain, and nausea after consuming dairy.

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Lactose intolerance is more common among non-Caucasian races, including Asian communities. This is because they usually do not experience the mutation in the 'lactase persistence' gene that allows for the production of the lactase enzyme to continue into adulthood.

The prevalence of lactose intolerance varies significantly across different populations. While it affects roughly 5-15% of people of Caucasian descent, primarily due to a genetic mutation known as 'lactase persistence' that emerged in Northern Europe around 7,500 years ago, the situation is starkly different in Asia. In countries like China, Japan, Korea, and Vietnam, the rate of lactose intolerance soars to an astonishing 90-95%.

According to Prof. Ronny Rachman Noor, an ecological genetics expert at IPB University, this disparity is rooted in evolutionary genetics. Non-Caucasian populations, including those in Asia and Africa, generally lack the 'lactase persistence' gene mutation. This mutation enables the production of the lactase enzyme, which breaks down lactose, to continue throughout adulthood. In contrast, traditional diets in many Asian, African, and American regions did not historically center around fresh milk consumption, meaning the lactase persistence mutation was not strongly selected for in these populations.

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The lactase persistence gene mutation that occurred about 7,500 years ago in Northern Europe allowed adults there to digest lactose well, so Caucasians tend to have low intolerance rates, only 5-15 percent.

Indonesia, situated in Southeast Asia, also experiences very high rates of lactose intolerance, ranging from 85% to 98%. The condition is present even in young children, with 21.3% of 3-5 year olds affected. This percentage increases dramatically with age, reaching 57.8% among 6-11 year olds, and continuing to rise through adolescence and into old age.

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In Asia, Africa, and most of America, the culture of fresh milk consumption developed more slowly and was not a major part of the traditional diet. As a result, the lactase persistence mutation was not strongly selected and remains rare in these populations.