There’s just no productive reason to eat a whole head of lettuce when you have access to a more diverse option of food.
You can’t be unaware about how humans interact with food. There’s all kinds of non-productive eating we do. The question I’m posing is “how is this one harmful?”
It’s basically just a bunch of water with some fiber,
Thats my point. Its pretty benign. Nothing bad or dangerous in a quantity a human could eat.
so it may also lead to some interesting bowel troubles later in the day
If eating a whole head of lettuce in a day causes you bowel troubles, I think you could easily argue your diet outside of the lettuce is much much more worrisome.