Corn Fed Re: Popcorn - Yes or No??

Isn't pellagra caused by eating corn to the exclusion of everything else? So if the rest of your diet is balanced, how could you get a pellagra-B12 deficiency? Or am I wrong and maybe the analogy is more like a carbon monoxide effect, where the B12 is rendered unassimilable? Could be, I don't know, never having been corn-fed (though I have been *called* corn fed). Either way, popcorn is one of life's main benefits!