I haven’t been to a functional doc. But I’ve been reading about it this past year. I’ve had depression for decades. And I used to be on antidepressants and antipsychotics. That isn’t what led me to dietary changes, though. I was a sugar addict for my whole life. And weight I had gained wouldn’t go away in my 40s. I had been decreasing sugar for a while. I didn’t make a big difference. Then I tried low-carb paleo. That helped a fair amount. Though I felt better, it was only when I when went very low-carb (keto) that I realized my depression had entirely disappeared. No moody funks, brooding, apathy, irritability, etc. Just gone. For all the doctors, psychiatrists, and therapists I went to, not a single one ever recommended functional medicine or anything like it. I never had any tests on much of anything. Most simply told me to take drugs.