There are a few responses one hears repeated when the topic of what foods are permitted and which are verboten on the ketogenic, low carb/high (LCHF) diet. In no particular order, the following jump to mind:

"I can't do that diet. I hate eggs."
"Oh, that's the high protein diet I've heard about"
"My doctor won't let me do that. She says my cholesterol will go sky high."
"What? No fruit?! That's a deal breaker."