If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one.
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.
Quite a lot people do start diets without consulting a physician.
The tongue-in-cheek answer would be to say that they are not in their right mind.
But I'd rather ask: Is it worthwhile to consult a physician before a diet change? Since, from my lay understanding, dietary needs are highly individual I'd say yes. Except for the dietary change the vast majority of people need: To consume fewer calories and more vegetables.