It is not thought that any food triggers or worsens UC. However, during periods of increased activity some patients note that certain foods (coffee, uncooked vegetables, popcorn) may make them worse. This is very different from person to person and should be discussed with your doctor.
There is some evidence that fish oil may be anti-inflammatory though the amount of fish oil that needs to be ingested is often quite large and difficult to take. The use of probiotics is controversial though some patients feel they improve when using them. These are also issues that should be discussed with your doctor.