If this were somehow true I would definitely not be a Dr.Pepper. Or a cranberry juice. Or a pickle. Or a shrimp. Not only are these foods that I really do not like and would never eat again, but that would make me incredibly sad if I were to become one of those things. Or apple cider vinegar, but that's more of a condiment than anything else so I'm not sure if one could turn into a cooking ingredient...
Not that I'm saying people should become cannibals because that is weird and personally freaks me out beyond belief and I do not endorse cannibalism in any way, shape, or form. Do not turn into Hannibal Lector my dear readers.
However if everything you eat is a vegetable then that makes you a vegetable and that's not a good thing when you know what a vegetable is besides a healthy treat of yumminess, or disgustingness depending on how you wish to look at it or what type of vegetable you are eating. But being a vegetable of a person is not something to be happy about, it is actually quite tragic.
And if you eat tacos does that automatically make you a Mexican? Or if you eat fish and chips does that make you British? And if I were to eat a danish pastry does that mean I'm from Denmark? No. No it does not.
I will never enjoy this expression. I have quite the everlasting dislike of it. Why am I blogging about this you may ask? Because someone I know actually took the expression seriously. Eat whatever you want in moderation, make good choices, live life as a person, not a watermelon.