hello weight reduction is necessary as hel strt gettin low back ache and knee pain....he can strt wid diet changes...hve small meals..and min 30 min exercise daily...no need to go fr vigorous things.. as far as gastritis is concerned...avoid oily nd spicy food...drink lots of water...avoid keeping stomach empty fr long....u can try sucralfate o syrup too...aftr food twice/thrice a day...if gastritis still persists u might need to get endoscopy done..meet a gastroenterologist