
19. Milk and yogurt upset your stomach
If you experience gastrointestinal or other symptoms after consuming milk or yogurt, you might be lactose intolerant. Lactose is the natural sugar in milk. To digest lactose, we require adequate quantities of the enzyme lactase. The trouble is, early humans lacked this enzyme and were unable to digest milk products.

An estimated 65% of humans struggle to digest lactose and milk products after infancy. This rate of intolerance is much higher in some areas of the world, with the rate as high as 90% in people of East Asian descent.
Symptoms differ in severity from person to person, but lactose intolerance usually manifests as gastrointestinal symptoms that are similar to those of IBS, namely cramping gas, bloating, diarrhea or constipation, and abdominal pain. The most obvious solution is to avoid milk products, but read product labels carefully as milk sneaks into thousands of products.