According to Chinese Medicine colon health is associated with depression. This science states every organ system is associated with an emotion and when our organs become out of balance so do our moods. If your colon is unhealthy you may be experiencing depression. So, get your colon healthy.
One way to do this is to follow the blood type diet. Why do I say this? I say this because, it is a low lectin diet. Lectins that react with your biochemistry in undesirable ways cause inflammation and deterioration in the colon. If you follow the blood type diet, and get on a diet that is compatable with your colon it can rejuvenate and heal your colon, thus making you feel more happy.
If you are already following the blood type diet and you are still not feeling the best you can feel, try eliminating gluten from you diet. Your blood type diet plan may not suggest this, but, you may also be gluten sensitive. This is one of the only flaws that I have found with this diet. But, it was picked up by Dr. D'Adamo (the creator of the blood type diet) when I went to visit him in person. Since, not everybody can visit Dr. D'Adamo in person, to get a more personalized diet plan, just experiment.
One indication of having a gluten intolerance, if having a more lines on the palms of your hands than people around you. The more lines you have on your palms the worse the integrity of your colon. This is something I discovered by going to Dr. D'Adamo's Clinic and also by studying the blood type diet myself, and becoming a practitioner. So, gluten may be causing inflammation and degradation in your colon, if you have a lot of lines on the palms of your hands.
Depression can also be caused from emotional causes, as well, as physical. If you are surrounding yourself with people and making life choices that don't support your soul's purpose or mission...you may start to feel depressed. You may feel like the universe is not supporting you and helping you on your path to happiness. Well, this is easy to change. Start looking at the life choices you are making and change the ones that surround you with these people or these events, as an after effect.