My paternal-grandfather, who lived to 102, when asked about diet responded, "eat variety, eat in moderation, have lots of colors on your plate"
Anecdotally, the folks I know who practice some kind of extreme diet, seem to spend an inordinate amount of time thinking about their diet. All that planning, charts, dietary interactions, classes, support groups, supplements, and books books books...it never sticks, they end up sick and it all seems to be just a giant waste of time and energy and potential.
Now I'm going to say something that's going to be offensive to many folks out there, but it's coming from a similarly personal place and it's about how people use their control of food as a proxy to control their lives.
This mechanism seems to show up in a wide variety of ways, extremely picky eaters, binge eating, anorexia, etc. Some rise the level of psychological or health disorder, some are just patterns and habits. One pattern that seems to show up over and over (and over) again is highly specialized diets for no specific health disorder.
My mother jogs from diet to diet every few years, she dives deep into the diet she's currently landed on: Atkins, Paleo, Gluten-free, Vegetarian, etc. buys and reads dozens of books, finds food sources, and restocks the entire house. Growing up I was fed under probably no less than 6 or 7 diets of this sort. My mother is a treasure trove of semi-scientific nutritional information and alternative medicinal practices.
My mother had a very out of control young childhood. She uses food and her diet as a mechanism to try and bring control to her life because that's something she can control.
I've found a similar pattern in my friends who also practice a similar relationship to food. Divorced parents, absent fathers, attention draining mentally-ill siblings, alcoholic parents, long lists of childhood illnesses, etc. all seem to be the backstories of the people I know who have intense desires to control their foods.
Anecdotally, it seems to be that these diets speak to a deep place in people. These diets, and the endless books and "information" available in these dietary communities seems to make them feel like if they can just learn the information in the diet, they can achieve some kind of control over that aspect of their life. It's like a complex OCD tick that's only satiated in this way.
There's some endless justification for it, ethics, or evolution, or morals, or health or whatever. But it usually seems to just boil down to people who want and need to bring what they feel is order to a life that's careening out of control.
It usually ends, like it does with all of my friends and family who go down this route, with some mysterious health problem that they try and solve by first doubling down on their diet, then is miraculously solved by just eating like a normal person for a few months.
And inevitably they'll start to overthink their diet, and find some other direction to go and the cycle will repeat. Because their feeling of wellbeing can't overwhelm their feeling of establishing control.
I've heard almost this exact story [1], word for word, dozens of times over the years.
[1] - http://kristensraw.com/blog/2013/03/17/my-vegan-diet-caused-...
Eating healthy is not that hard, and it doesn't really require that much thought or time. You don't really have to read lots of books on the subject, or adhere to an ideology, write blogs, or read food manifestos.
Just "eat variety, eat in moderation, have lots of colors on your plate".