Cho shouldn't count calories
Between Rod stacks, Overgrowth, levels, etc the damage on Feast goes up nearly constantly, and it's awfully embarassing when you leave an enemy champ with 10 health because you accidentally carried a 2 in Cho's food diary.
In an ideal world, digestible champions would be marked (ala Urgot's Fear Beyond Death) and in a perfect utopia this mark would replace their character model with a roast chicken. As this would take time and energy away from legitimately more important aspects, simply updating the tooltip on Feast to show the total damage (instead of just Base + AP + Health) would help Cho chow down without first going to the blackboard.