My diet is very consistent, and I have maintained my weight of 139 lbs since I started taking control of my life, my disease, and my overall health. I kept a food journal for a year or so, beginning in 2006, and omitted wheat from my diet. The extra pounds stayed off, and I am healthier now than I was in my 20s-30s (I am 55). Daily yoga (15-20 minutes with Rodney Yee DVD called “AM Yoga”) and exercise (45 min a day, and a variety including walking, hiking, running, biking, yoga, tennis, etc.) help keep my weight consistent.
The question of willpower, for me, is almost a given: I follow a strict diet, and eat “food with one ingredient” (mostly), and no refined sugar at all (I do use honey and a bit of maple syrup).
Since most of the body’s serotonin is produced by the enteric nervous system, I feel better emotionally, too.
Here is a link to a good diet overview from the ccfa.org. They even mention the SCD diet, which I still use, in moderation.