Sometimes its not how much we eat but what we're eating. Maybe try an elimination diet to weed out problem foods. Many have trouble with wheat, soy, dairy, or nightshades.
I have had tummy troubles most my life, which caused mood issues. I had the celiacs/ gluten test and it came back neg. But when I eliminated grains, magically much of my problems disappeared. I ended up discovering no dairy, nor grains = stable mood more energy, no IBS symptoms or bloating, and a quick 10lb weight loss.
But everyone's system is different, so you have to find out for yourself.
Open your mind and take a look a paleo/primal. Eat the way humans have eaten for 100,000 years, not the 10,000 year old agriculture diet, or the 60 year old low fat diet.