I think there are other plausible answers, and I'm generally skeptical of people who believe there are diet cure-alls, especially for depression. I'm not a psychiatrist, but I do have a bipolar 2 diagnosis. I only found out it wasnt a unipolar depression because I had a hypomanic episode. I can only describe a hypomanic episode as a wave of constant energy, and I've also heard it described as: 'being on meth for a week straight'. It gave me the energy to forego food for multiple days because I didn't feel the pain of hunger pangs. I also didn't sleep for a few days, not because I wanted to, but because I just had too much energy.

I'm not a doctor, but hopefully this is an example of other places to look that aren't diet related.