In India, milk is just as indispensable. For many, it begins with a glass before school and continues into adulthood through endless cups of chai. It is widely available and bound to cultural rituals, from festive sweets to everyday meals.

That said, it’s not uncommon to also hear people say that drinking milk makes them sick to their stomachs—literally. In fact, many people claim that their health only improved after they cut milk from their lives. For some, the culprit is milk intolerance, which can show up not only in digestion but also through acne, sinus allergies, chronic fatigue, brain fog and general inflammation.

I’m one of those people. After experiencing frequent gastro upset, fatigue, and a host of other unexplained issues, I decided to study molecular nutrition. What I learned about the common side effects and health issues associated with regular cow’s milk consumption inspired me to reduce my own consumption—and what followed can only be described as a change in my physical condition for the better. Below, a look at all the reasons I decided to give up milk, and what happened once I quit.

The impact of casein on the intestines

Casein is the main ingredient in milk—it accounts for about 80%. Though casein is a type of protein that contains a very large number of amino acids, it has also been linked to intestinal inflammation. Casein is actually now thought to be one of the causes of milk intolerance or dairy sensitivity.

There are several types of casein. Type A1 casein, which is found in many types of milk—especially in the milk from cows that originated in northern Europe, like Holsteins—is particularly prone to causing inflammation of the digestive tract, as it’s difficult for humans to digest. This undigested casein ferments in the intestines, producing gases and inflammatory substances that irritate the intestines.

On the other hand, A2 casein—which is mainly found in Guernsey, Jersey, and other cow breeds that originated in the Channel Islands and southern France—is considered relatively easy to digest and may cause fewer symptoms in people who are more likely to react to A1 casein.

Unless labelled “A2,” most regular milk contains both types of casein, meaning most milk can be difficult for a lot of people to digest. “Consumption of milk containing A1 beta-casein was associated with increased gastrointestinal inflammation, worsening of post-dairy digestive discomfort symptoms, delayed transit, and decreased cognitive processing speed and accuracy,” one study that looked at the effects of casein on the gut and brain reports.

Lactose intolerance

Lactose is a sugar found in dairy products. To break it down efficiently, our bodies use the enzyme lactase. However, the body’s ability to produce its own lactase often declines with age, making lactose difficult to digest—especially as we get older.