If I were your treating doctor I would advice you for cholecystectomy first better go for it rather consultation regarding diet. Among diet you can take anything just remember to take low fat and low cholesterol diet and no alcohol, other than these you can use appetizers like nusowin drink, aptivate syrup before meals for weight gain, boss powder and ensure powder is basically protein and vitamin powder it is also a good supplement for weight gain. But as far gall stones are considered gall stones form due to gall bladder non functioning and other factors once gall stones are formed there is no function of gall bladder in general so better remove it before its complications sets in. Hope I have answered your question. If you have any further questions I will be happy to help