Our brain depends on neurotransmitters to transmit signals. Neurotransmitters are made of animo acids, which come from protein in our food. Brain is protein dependent, it needs amino acid, which makes up protein, to manufactures these neurotransmitters.
Neurotransmitters that regulate mood also regulate our appetite. When we become deficient in our neurotransmitters, we start craving carbs and sugars. The more deficient, the more cravings we have for bad carbs such as refined sugar and processed carbohydrates.
If dietary improvement is not enough to relieve the depression and anxiety and to counteract the cravings for "bad mood foods" such as refined carbs, sugar, corn syrup, fructose-based substances etc. , then supplementation may be necessary. This is called amino acid therapy-the process is to identify negative mood and see what nutrient supplement that are most useful for the symptoms.
Most common reason for depression is serotonin deficiency. Precursor of serotionin is tryptophan , which is the first to be lost in a low calorie diet. It is most common for people who skip meals and are addicted to empty calories.