try essential fatty acids, as our brains are 60% fat, many derived directly from efa's. canola and corn oil i find are very good sources, nuts may be better, but depending on the severity of the disease, they may not digest nuts at all, so corn oil and canola oil are good for someone who cannot digest nuts.
essential fatty acids are polyunsaturated fatty acids alpha-linolenic(omega-3) and linoleic acid(omega 6). my own anger issues became better once i started getting closer to my RDI in EFA's. The average adult needs about 1.7 grams omega 3, and 19 grams omega 6.
I take half the RDI, as i find if i go any higher, it actually leads to more depression, i believe that is because in active disease state, or possibly even inactive, we produce more free radicals then the typical person, then these fats tend to become oxidized, this is something you will have to test to prove to yourself. ingesting more antioxidants may counteract higher intakes of polyunsaturated fats.
Then try taking a b12 supplement, as crohns typically involves the ileum and severely interferes with not only its absorption, but in maintaining those levels. we have a much higher requirement for b12 then normal people. i need to replenish mine every other day, i find that none of it is stored and i quickly become depleted and feel low energy after a few days. adenosyl cobalamin is stored better then methylcobalamin, i take about methylcobalamin every other day and adenosylcobalamin every 4 days. but perhaps its easier to start out with cyanocobalamin, as your body can convert it into either form as needed, but i prefer the preformed and i divide them into ratios that agree with my body. our body requires both forms methylcobalamin and adenosylcobalamin, there is a third form called hydroxycobalamin, these are all the forms in meat/fish/seafood. cyanocobalamin is a synthetic form, which can be converted in the human body.
magnesium is also another major mineral involved in depression, and is frequently depleted in crohns disease, i take magnesium citrate daily, it takes away 50% of my depression within hours. but since i take it daily, the lows arent really low at all!!!
those are probably the most likely dietary issues someone with crohn's may have, depending on the severity of course.