Blasting is a great way to address the symptoms associated with gastritis. It is important to monitor and understand which foods cause irritation as everyone can be different with what they can tolerate. Including anti-inflammatory foods can help soothe the body. Check out this article for some great tips:
The foods listed by SIULOPEZ are also great to include!
Additionally it may be important to provide low fiber foods during a flare up where he may be experiencing diarrhea. Include foods like bananas, oats, peanut butter and coconut water.