A few years ago, I went on a ketogenic diet as well and noticed my mood was much more level and steady. Eventually when my depression went nuclear, I went back to full on carbs, also gained a lot of weight as well.

Not a scientific study by any means but I have noticed that too much sugar and white flour seems to coincide with mood being either unstable or very low. It's kinda of a chicken or the egg type thing, I'm not sure if the mood drives the craving or the cravings bring on the mood difficulties. They both seem to occur at the same time.

Right now I'm trying to take a more moderate approach, still eliminating grains and really starchy vegetables (like potatoes, yams) but including a lot more carbs from veggies (cooked and fresh).