I wish it were something that could be solved by food choices. So, there is some suggestion of the connection between the gut and the brain. Perhaps you have heard about autism improving with gluten-free/casein-free diet. I have read about connections between leaky gut and bipolar, but I have healed my gut partially and haven't had improvement in my bipolar. Also, I have had bipolar since I was a child (IMO) and I don't think I had leaky gut to begin with. Anyway, I think that obviously sugar and carbs can affect your blood sugar which can affect your mood. I also think if you have any food allergies (known or unknown) that those can affect your mood. I did a whole30 to pinpoint some of my allergens, if you are into that sort of thing. It's an elimination diet. There is also the GAPS diet (Gut And Psychology Syndrome) that focuses on healing the intestinal lining. I could go on an on or offer more tips if you are interested, but those are the major things I have gleaned in my research.