I get that, and I disagree. I think the discussion about food should happen first.
The food you eat affects your chemical balance, and therefore your ability to process information when you are making a decision or analyzing a situation by overloading your circuits.
You can actually try this by eating a bunch of sugar and carbs for a few days, and then going without carbs or sugar for a few days. I guarantee your ability to process information will change, and your personality probably will change as well. If you have a spouse or roommate, ask them if they notice - I'll bet they will.
My point is about causality. We are basically (no pun intended) a big bag of chemicals, and those chemicals are used by our brain to do its work. Simply having the wrong level of salt in your body (not just NaCl, but any salts) can significantly affect your brain.
I just looked up the word because I couldn't remember it, but Hyponatremia is caused by not enough salt in the body and can make your brain physically swell. Think about that for a moment - just one chemical can make your brain change in size - imagine what the effects are from all foods you take in.
So to me, psychiatry has it wrong. It's like a mechanic trying to diagnose why your engine doesn't work when you put molasses in the gas tank, or why a heart surgeon talking to a 500 pound obese person and without discussing their eating habits. Why should the brain be any different?
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EDIT - Check out this page at the Mayo Clinic [0]. They list some of the symptoms of hyponatremia, which include, * "Confusion, Loss of energy, drowsiness and fatigue, Restlessness and irritability "*
[0] - https://www.mayoclinic.org/diseases-conditions/hyponatremia/...