All depression (and most other mental problems) is caused simply by a combination of stress and poor nutrition. A downward cycle with the stress requiring more nutrition, and the lack of it causing more depression.
There are two "hidden" sources of stress, and one other partially hidden. The two hidden (to most) are allergy stress, and toxic mineral stress. I've discussed these before.
Testing for these is difficult and few people know much about themselves in this regard.
Allergy stress is the most common, and the most difficult to test for, and even more difficult to solve.
Neuroliminal Training and Neurofeedback both solve this particular stress, albeit slowly. It can take a few years to solve ALL such stress, and the unconscious mind has it's own priority as I've learned over the years. Few people can afford Neurofeedback for this amount of time, so, NT, at it's single cost is considerably better.
The world is becoming more toxic with minerals affecting health and levels raising all the time. Autism is an epidemic in only a few years from mercury.
Depression from mercury is increasing as well as other minerals.
Toxic mineral stress is somewhat simpler to test for. There is blood testing which measures what is in the blood at the time to taking, and this changes by the minutes and hours. Urine testing, particularly collected over 24 hours, is more accurate. Being a PhD, and not an MD, I prefer hair analysis which is also not that accurate, but it does give a better picture of toxic minerals overall IMO.
If you think your depression is from any of the above, I urge you to go to http://drbate.com/Ref/articles.html
Download the article "Integrated 4 Part Therapy for Autism and Other Mental Problems." Read that, understand it, do it, and you will also solve any form of depression, along with two of it's worst symptoms, insomnia and anxiety.
Now, let's talk about a very different depression that is less understood by MD's. It's caused by hypoglycemia which is docterese for low blood glucose getting to the brain.
Many persons have the "sugar blues" a few hours after meals a lot of the time. It seems that sometime after eating sweet things, these people get a sudden dip in the glucose (blood sugar) as the stored glucose runs out, and the body tries to make glucose out of sex hormones.
It's called "Sugar Blues", or hypoglycemia. And it's not so hidden. This is often an individual reaction to the hypogycemic "dip" that occurs typically at some period after eating a high carb meal. This dip may make a person actually pass out, or come very close to that.
I wrote a paper for the Behaviorist newsletter in the early 80's showing that adult onset phobias were most often caused by that hypoglycemia dip, particularly driving phobias.
If a person is driving over a bridge, and they nearly pass out (not uncommon with this "dip"), they may develop a driving phobia to bridges or tunnels. Or simlpy driving.
Here's the physical side of this. You eat a very high carb meal. Humans are not designed (or evolved enough) to get that much sugar that fast, and so, your body releases insulin enough for three hours of sugar digestion, but it's all coming in less than one hour, so way too much insulin is released into the bloodstream "pushing" glucose into cells, and lowering glucose supply to the brain. (The brain lives on glucose and oxygen, and lack of either causes panic.)
The body counters with releasing adrenaline which then releases the stored sugar needed for the flight or fight response emergency. This works to counteract the too much insulin until the stored sugar runs out. Now, the body starts to change hormones into sugar for the "emergency". But this takes time, even several minutes sometimes, and the glucose supply to the brain is lowered, sometimes drastically. The brain can even shut down (fainting). Scares the hell out of you, and whatever you are doing may become associated with that scare, even creating a phobia.
If you eat an apple, it takes about 3 hours to digest it in the gut, and get all the sugar and nutrition out of it. The body senses it's an apple, and from experience, releases enough insulin to cover those three hours, and your glucose jumps for the first few minutes of eating, but fairly quickly goes back to normal, and stays there for the three hours.
Now, juice that apple, and get all the sugar immediately. This looks like a bushel of apples, and insulin is released to cover that much. Way too much, and the initial up turns into a fast down. Now, because glucose is essential for energy in the brain, several systems start to kick in. First, adrenaline, then converting fatty acids to glucose.
I's called hypoglycemia, but it's really hyperinsulinism. Your body released way too much insulin because it was fooled by modern technology.
This is the origin of "Sugar Blues", and it can happen to any one of us.
If you suspect that you may be depression after meals, or eating sweets occasionally, get a Glucose Tolerance Test (GTT). Do it for at least 5 hours, and check any and all symptoms whenever they measure. Also, there is a measured amount of the horribly sweet drink used, and too many MD's and hospital nurses simply give the patient the whole bottle. As a 6 foot man weighing around 200 pounds, I take only 6 ounces out of the 10. For a child, that bottle is way too much, and too many MD's don't know it.
If this should be even part of your problem, here's the way to solve it. Make up a ziplock bag with a bunch of peanuts (or other nuts) and raisins, about 4 nuts to every raisin. Every two hours after eating a meal, take a small handful of this mix, and eat it. The nuts give you long term sugar, and raisins give you short term sugar.
I once saved a marriage with that simple advice. He got angry with her every afternoon at work after a high carb lunch.
I hope that I've helped you and/or yours. Please feel free to copy the above and send it to friends or family. MD's don't recognize hypoglycemiaas as "disease" because it really isn't such. It's our diets that are wrong for our bodies.