40 ml of GFR means chronic kidney disease (CKD) stage 3. Avoid routine pain killers called NSAIDS. Blood pressure needs to be kept below 130/80 mmHg. As for diet is concerned calories should be 35 kcal/kg body weight, proteins 0.7 gm/kg, salt 3 to 4 gm/day, depending on BP and swelling. Should stop smoking. Cholesterol and other lipids should be kept below targets.