It doesn't matter how much you eat if you are not absorbing it.
Maybe a diet that restricts foods that aggravate (or even cause) the disease.
Most diets that i have seen people claiming good results for share a few basic similarities:-
No Cereal grains with a high gluten content
Limited or no Cereal grains without gluten, but are dense and high glycemic index, and contain other anti-nutrients (rice seems to be the safest)
No Sugar and fructose (limited use of natural sweeteners)
No Foods with nutrients / fibre removed – grains, sugars, refined carbohydrates
No Vegetable seed oils, chemically extracted, high in omega 6 and damaged / oxidised fat
No Added synthetic chemicals, flavours, antioxidants, sweeteners, colours, preservatives
The diets that work (SCD, Paleo, GAPS -in my humble experience) are usually very low carb (they exclude all foods high in carbs -grains and tubers) but there is recent evidence that rice and tubers are well tolerated and do not shorten remission
This diet doesn't limit carbs, It is a well balanced diet and a good starting point -
http://perfecthealthdiet.com/2010/07/ulcerative-colitis-a-devastating-gut-disease/