Title: Can You Become Lactose Intolerant After Eating a Vegan Diet?
Headings: What is Lactose Intolerance? Can You Become Lactose Intolerant after Eating a Plant-Based (Vegan) Diet?
What is Lactose Intolerance? Can You Become Lactose Intolerant after Eating a Plant-Based (Vegan) Diet?
60% or more of humans are lactose intolerant.
Lindsay S. Nixon

Content: Those with lactase persistence have a genetic mutation either from European or African ancestors. Small populations of African peoples were historically cattle herders, and that's where their lactase persistence genes come from. The European mutation appeared approximately 7,500 years ago in dairy farmers who lived in the Funnel Beaker region. Today, the highest proportion of people with lactase persistence live in Northwest Europe, especially the Netherlands, Ireland and Scandinavia, though research suggests that dairy farmers carrying this gene variant probably originated in central Europe. ( Source)
Back to the original question: Why would someone experience "lactose intolerance" symptoms after being dairy-free for a short period? I'm not a doctor, nutritionist, or scientist — but I think the reality is you were always lactose intolerant and you just didn't know it. I've worked with dozens, if not hundreds, of clients who after they cleaned up their diet, realized things they thought were "normal" actually weren't. A common saying among them is "I had no idea how sick I was or how awful I really felt until I knew what it was like to feel well and thrive." Many of my clients used to experience bloating, gas, diarrhea, heartburn, and other unpleasant things that they thought were "normal" and then, after switching to a plant-based diet, realized that wasn't normal and they didn't have to experience those discomforts.