Don't worry, they'll tell you. I take it that is the answer you were looking for.
Not always the case - my grand daughter has a vegan diet and never tells anyone - just gets on with her life - doesn't seem to do her any harm given that she's winning plenty of races on her track and now gravel bikes
anyone with half a functioning brain would always seek out supporting and contradictory evidence to any 'claim' - whether that's about food or any other thing in life