Why Are So Many People Lactose Intolerant?

Humans are the only mammals who eat dairy into adulthood.

Dr. Linda Dahl


Photo by Mae Mu on Unsplash

When I was a junior in college, I thought I’d developed an ulcer. I would get gnawing gut pains, sometimes accompanied by burping or bloating. I looked up the symptoms in a textbook (there was no internet in those days), and all signs pointed to acid reflux. It made sense, what with all the stress I was dealing with in my pre-med classes and work-study. I could almost feel the acid burning a hole through my stomach.

The remedy, I had read, was to eat a lot of dairy. It was thought to “neutralize” acid. That sounded great to me. My favorite meal was ice cream. On really bad nights, I would scarf down an oversized chocolate peanut butter cone in place of dinner and try to convince myself I felt better. To my surprise, my symptoms got worse. I even started getting diarrhea. And the gas–so noxious it would have knocked out Arnold Schwarzenegger. (Terminator 2 was super popular back then.)

One day, I asked the medical student in my research lab what she thought.

“Lactose intolerance,” she diagnosed, confidently.

“What’s the treatment?” I asked.

In the days before Lactaid, her answer was funereal. “Stop eating dairy.”

She may as well have told me to stop eating everything. As a midwestern girl, my entire diet was coated in cream. How would I survive?

I’m sure you’ve heard of lactose intolerance. It’s a condition where you lack the enzyme lactase, which breaks down lactose, the sugar found in dairy products, like milk, yogurt, cream, or cheese. Without this enzyme, undigested lactose passes into your colon where gas-producing bacteria devour it, letting off gas that causes the associated symptoms of bloating, flatulence, nausea, abdominal pain, and diarrhea. Not everyone with lactose intolerance has terrible symptoms, but some (like yours truly) really suffer.

Interestingly, nearly all newborn babies make loads of lactase when they are born. They need it to digest breast milk (or animal milk if breastfeeding doesn’t work out). But once they wean off the udder, lactase production goes way down. Quelle horreur, you may think. How are we supposed to eat frozen…



Dr. Linda Dahl

Physician. Author of Tooth and Nail:The Making of a Female Fight Doctor & Better Breastfeeding, http://www.drlindadahl.com @doctorlindadahl