Why Milk Makes You Sick: The Truth About Lactose Intolerance

Dahyun Kim

June 20, 2025

Lactose intolerance, also called lactose malabsorption, is when you are not able to fully digest and consume the lactose, which is the sugar in milk. According to Mayo Clinic, the enzyme produced in lactase, small intestine is responsible for lactose intolerance. Although you can digest dairy products with low levels of lactase. If you have severely low levels, you become lactose intolerant, showing symptoms after consuming dairy products. National Health Institute states that most people have primary / secondary lacotse intolerance, where they are not born with this condition; they develop it after infancy due to changes in diet and environment or disease in small intestine. Only about 40 cases worldwide are reported to be congenital, meaning having this condition from birth. About 68% of the world is population has lactose intolerance, it being more prominent in East Asians, Hispanc/Latino, and African Americans. Statistics show that over 80% of East Asians and 70% of African Americans are lactose intolerant. On the other hand, Europeans tend to show less percentage of lactose intolerance, approximately only 25%, only 5% being Northern European due to historical patterns of dairy farming and natural selection according to Nature. 

Symptoms vary depending on individual’s lactase level, but it is pretty similar. According to Mayo Clinic, the few common symptoms are: diarrhea, nausea with vominiting sometimes, stomach cramps, bloating, and gas. While these may not be extremely painful, it will cause discomfort to some extent, limiting people’s diets. Limit of diary products in diet may not effect people directly nutrition wise but those with lacotse intolerance will have to find an alternative to consume calcium and vitamin D that is absent from not consuming dairy products. 

How do people know if they are lactose intolerant? Sometimes, this is pretty self-explanatory as you will not feel well after eating things such as ice-cream, milk, cream, etc, anything that has to do with dairy. However, for more exact observation and results, there are a few tests that can be conducted, mainly focused on the blood sugar level. According to Mayo Clinic, the two main tests consist of Hydrogen breath test and lactose tolerance test. Hydrogen Breath test is where the doctor will measure the amount of hydrogen in your breath at regular intervals after you drink a high-lactose liquid, and once you breathe out too much hydrogen, it indicates that you are not able to fully digest and absorb lactose. Lactose tolerance test takes longer, where you will undergo blood tests to measure the amount of glucose in your bloodstream after drinking high-lactose drink. If your glucose level stays stable, you are not able to digest the drink, indicating symptoms of lactose intolerance. 

As common as this is, there are many products that lactose intolerant people can use as an alternative these days, such as lactaid before eating dairy products to alleviate the after symptoms and discomfort, and lactose free products.