It's true that for some people diet can be the primary factor, but that is certainly not true for everyone. This is one of the reasons depression is so difficult to treat. The causes can be anything from diet, lack of exercise, trauma, to a genetic predisposition resulting in brain chemical imbalance.
If there were a simple answer, there would be little clinical depression. I inherited the chemical imbalance from my father and a simple diet change would have little effect on treating the disease. Two years of drug treatment did restore the proper balance to the point that I no longer needed to continue the drugs.
That worked for me and, as long as symptoms don't return I won;t need the drugs. It's been about 3 years or so since I was weaned off the drug therapy.
Unfortunately, the nature and various causes of the illness means that what works for one person may not work for another. One drug can work wonders for one, and do nothing for another. Diet changes may help one person dramtically, and do zilch for the next.
It's a very difficult illness to nail down.
