There are countless examples of past doctors claiming that psychiatric disorders are caused by some simple dietary issue. You can find people claiming that everything can be fixed by ketogenic diets, vegan diets, carnivore diets, Vitamin B12, niacin, magnesium, fish oil, you name it. For any vitamin or diet there is someone out there making passionate claims that it solves everything.

None of these hold up under actual studies. It’s the domain of wishful thinking that sadly preys upon people desperate for answers. Some times the placebo effect works for a while, but usually people just end up with a cabinet full of supplement bottles and a history of fad diets with no progress on their condition.

The dietary issue is infection (usually two or more, basic shit like candida in the gut, mold exposure, EBV recurrence, Lyme, parasites, more) causing systemic malnourishment, and lack of homeostasis, causing nervous and endocrine issues/misfires,

(at which point you'll often notice immunodeficiencies, minor "unexplainable" abnormalities in bloodwork),

and indeed cognitive issues, depression, anxiety, and other more severe brain malfunctions.

> None of these hold up under actual studies

I agree with you overall, but interestingly, research really has found a link between lower Vitamin B12/B6/B2 levels and ADHD. Also lower Vitamin D, and delayed circadian rhythm. You certainly can't use supplements as a replacement for stimulants but they may help.

A sizable (3-10%) part of the population can either not digest lactose or has a significantly reduced ability to absorb fructose in the gut. The resulting fermentation and low dosing of low quality alcohol can cause cognitive symptoms which can be totally alleviated by appropriate diet.

It is easy to test (drink a sugar challenge drink and measure H2 in breath) but as it is time consuming and not profitable rarely done.