When you eat blueberries, the anthocyanins - those fancy antioxidants that give them their signature color - aren't fully absorbed by your body. Instead, they make their way into your digestive system, where they can cause some pretty cool (and weird) effects.
As the anthocyanins move through your gut, they can bind to other compounds and create a range of colorful byproducts. And, yes, that includes the possibility of turning your poop a blackish or dark purple hue. But don't worry, it's totally harmless - just a fun little side effect of eating these delicious berries!
But here's the thing: beets and rhubarb can also cause similar color changes in your stool. So, if you're eating a rainbow of fruits and veggies, you might notice some pretty wild and wacky things happening in the bathroom. Just remember, it's all about the pigments and how they interact with your body.