Diet discussion is a sort of taboo in ME/CFS.
Is it? I haven't noticed that. Claims that "diet x will work for everyone!!!" aren't appreciated, since we haven't seen any evidence supporting such a thing. However if someone says that grapeseed oil gave them a benefit, or that avoiding <whatever food> helped, I generally accept that. I generally don't give the same diet a try, since the likelihood of it working the same way for anyone else is fairly small.
Claiming that "diet is the one true answer" is no different than claims for a drug or technique. It's not "the one true answer" until it's proven in large numbers of people.