Good point, I agree that the analogy is not perfect, but I don't agree that Nutritionism is equal to the faux sciences you list, everything you listed has a philosophy that at it's core is faux science, the philosophy of nutritionism says that what we eat and how much affects us. It's the individual nutritionist that may base their philosophy either on real or faux science. Dietician:Nutritionist and Sports Science:Fitness Trainer is probably a more accurate comparison.
But then how do you differentiate between the people who believe in the magic healing power of $FOOD_DU_JOUR and someone who's based on science? That's the difference between a dietician and a nutritionist.
A Fitness Trainer is not a good analogy either, because you can't stay in business long as a fitness trainer if you have no idea of the basics of fitness or anatomy. E.g. a fitness trainer who said that you breath through your feet, so you should wear sandals when running knows as much about biology as a nutritionist who thinks chlorophyll can oxygenate your blood. However the magic super food nutritionist had a prime time TV show! High ranking, popular nutritionists can believe things that are nonsense, what hope do you have about a local nutritionist?
A fitness trainer who believes you breathe through your feet would probably suggest you run barefoot. Hey what do you know, he's just created one of the most popular running fads (although this could go with running barefoot or in sandals, as both are popular among hardcore runners).
And dietician's pushed the traditional food pyramid for years, which many current dietician's find fault with, years after nutritionist's pointed out the same thing.
I've met successful doctors, lawyers, trainers, etc., that believe in crazy wild theories that have no basis in anything other than what they want to believe. Success amazingly often has very little to do with if people are right or wrong (I'm sure there are some very wealthy astrologers out there).
By your theory, it doesn't matter which doctor you pick, they are all trained physicians, so they all believe the exact same thing. Need a psychologist, just read Dr. Phil's book, he's board certified. Or don't agree with Dr. Phil, then all psychologist's are bad.
True. I'm a med student who loves nutrition. Here in germany the DGE forces actual dieticians to use extremely outdated information (they HAVE to adhere to their handbook). The official curriculum is 30-50 years behind current state of research
And don't get me started on surprising amount of doctors that have no concept of science at all. They just say: "Wer heilt hat recht!"/"Who Heals is Right!"
Ask for proof. Competent people will be able to provide it. And explain it logically in depth.
Fitness trainers believe amazing amounts of bullshit. And teach that nonsense.
There are less than 1 % of trainers that have a decent knowledge of anatomy or of how to train you for maximum results. Their real job isn't delivering results, but keeping you busy and "motivating" you.
I get what you are saying, but formal education only tends to weed out the absolute nutjobs.
Just look at Dr. Oz or Charles Poliquin. Completely crazy.
TLDR: Ask for proof. From my experience you overestimate the impact of formal education.