There's a connection between the solar plexus (not the chakra, but the actual nerve group), the vagus nerve, and depression. An over active solar plexus is depleting to the neurochemistry, but in these people appetite is heightened because there is a more stimulatory action happening to the vagus nerve. There's also an underlying nutrient deficiency, but because these people pleasure eat, they seldom eat the right foods to correct the imbalance. It's kind of like how whole grain bread contains 0.002% of your RDA for iron, and if you're iron deficient you'd just eat bread all day to get at that small bit of nutrient. In this group, their depression can be cured with targeted nutrition. Nutrient rich with moderate calories. There's usually also blood sugar imbalances in these people -- livers that don't store sugars properly, so hypoglycemia pushes them toward sugary foods.
The reverse is people who have low solar plexus activity, probably due to depleted neurochemistry, so they have no appetite, and so their mood-lifting neurotransmitters don't get restored as easily. They're sluggish, have poor lymph clearance, are under-active and "just can't". They'll ultimately have nutrient deficiencies but the origin of their condition is endocrine, usually at the onset of puberty. You fix these people by giving them low dose metabolic adaptogens, like ginseng, or digestive bitters.
Pre-cursors to neurotransmitters like serotonin are made in the gut, and the link between appetite and mood is pretty established through this understanding. If your gut isn't healthy, your brain won't be healthy. The solar plexus is also the emotional center... so people with intense experiences or trauma often have down-regulation to that aspect of the body. The solar plexus / brain feedback loop therefore becomes dysfunctional or incomplete.
It's true that fasting detoxes the body. Hippocrates would ask every patient to fast for a time (usually 2-3 days) in order to clear excess from the body, so that the true condition would emerge. Based on what he could see, he would then prescribe appropriate treatments. This method was used all the way until western alchemy was endorsed in the 13th century, which tossed out the Hippocratic system completely. A shame, because it had its uses.
I don't think depressed appetite is a fasting thing though, it's an imbalance in of itself. People with suppressed appetite still eat, just not as often. Their systems are really sluggish and stagnant and motility is a bit of a train wreck. Most of them are de facto fasting, but not by choice, so it's not the same thing. Their bodies have a low basal metabolic rate, the internal organs are sluggish, and the hunger mechanism is suppressed. The organs can't handle any burden, including food itself.
However, I am trying to just live for the good days and maintain a semblance of tolerance and compassion for myself - it's the only panacea that, although not ideal, works. 
