I'd like to encourage anyone feeling depressed to take a good, hard look at their diet and to consider the possibility that they lack some essential nutrients.
I'm not saying that a poor diet or lack of nutrients will necessarily be the only or even the main cause of depression, but these factors could have an impact (sometimes a profound impact) on the severity or frequency of depression.
For most of my life I've had a pretty poor diet, and while I knew diet could affect one's mood, I really didn't realize how profound an effect it could have until poor health recently forced me to make drastic changes in my diet and to consider and study the potential effects of diet on mental and physical health.
What I learned was that many, many nutrient deficiencies could have very severe consequences on one's mental (not to mention physical) health -- including depression, dementia, and even death. Symptoms of a nutrient deficiency are not always obvious, and some of them take a long time to manifest -- so long that they kind of sneak up on you and you could almost feel like what you're experiencing is "normal" or just the way you are (ie. depressed, just because you have a negative outlook on life).
Once I improved my diet and started taking supplements for essential nutrients which my diet still lacked, I felt so much better, and have had much more energy than I'm used to, don't need as much sleep, and my mood and motivation have dramatically improved.
I now firmly believe that many people who suffer mental issues, including depression, may be malnourished or nutritionally deficient in some way. Taking one's diet seriously, reading up on it, and improving it could really change your life.