The canned drink can be counted, but to what extent I dont know, and may not be totally equivalent. I know liquid intake in general should be 80 percent liquids by mouth, and 20 percent liquid through food in a perfect world, and someting is better than nothing, but doubt you are over hydrating him, if consuming 48 ounces is difficult, vomiting, and just using protein drinks. My intake should be 16 cups daily, which equals 128 ounces, according to this calculator. I usually went by half my body weight, 180 lbs (90 ounces) plus factor in food by 20 percent, which is almost the same. My glucerna 1.5 cal is 8 ounces, so x that by 6 daily is only 48 ounces, so 80 ounces is still needed to be consumed, but needs are different due to activity, health status. The 500 calories x 6 is in the range, which needs generally vary from 2500 -3000 or even higher. Maybe see the nutritionist at the hospital, who can advise best.