Since when do you have to be God Almighty to utter a legitimate truth? You already admitted the analogy was valid. You just claim it's fallacious because it conflicts with your doctrine and you can't find another out than pretending the person uttering it is contradicting God when what they really are doing is contradicting your interpretive doctrine.
You need a reading comprehension course. The only way it could be valid is if the nutritionist had God's authority and credibility. That point was made. No one does. Again, broccoli isn't 'good' for everyone, God's Word OTOH is, unless that contradicts Catholic doctrine.
Later you spoke of truth. Now I know this is again from the Bible, John 17: 16 They are not of the world, just as I am not of the world. 17 Sanctify them[b] in the truth; your word is truth. 18 As you sent me into the world, so I have sent them into the world. 19 And for their sake I consecrate myself,[c] that they also may be sanctified[d] in truth.
God's Word is truth, not Catholic doctrine. But what does Jesus know?