I think I had some level of depression/anxiety my whole adult life. Actually, probably even as early as elementary school. I was never completely incapacitated by it, though, and so I was reluctant to get any professional help. My sister had a serious drug problem into her 20s and then spent 15 years looking for the right kind of therapy and anti-depressant. She eats an above average SAD and is pretty happy with where her prescription meds have gotten her.
I started out losing weight on a SAD calorie counting plan and found that the foods that were working for me were mostly primal. As I ate more and more primal and less and less processed food, my mood really changed! At one point, I was so worried about how different my mood was that I started to wonder if I was actually bipolar and I'd just gone from some 20 year depressive episode to some kind of mania. After about 6 months of feeling amazing, I don't think I'm delusional and I haven't done anything really stupid, so I no longer worry about mania. This is just how a normal person feels, I guess.
I'm not super strict, either. I probably eat a single portion of wheat twice a month, a single portion of rice 2-4 times a month and (a few non-wheat) beers every weekend. My carbs are typically between 100-150/day, but can range from 75-200, depending on whatever. I've just started playing around with dairy, because it may be that my daily 1/2C of yogurt is messing with my digestion. As far as I can tell, though, it hasn't impacted my mood.
CW-125, part calorie counting, part transition to primal
GW- Goals are no longer weight-related