Absolutely nothing.
So Zenimax indicated they wanted to make drink buffs competitive with food buffs rather than making it so people can use both. Well after seeing what they've done to both, and asking around pretty much everyone I meet, I have to conclude that pretty much no one is using drinks over food. Which is exactly what is happening prior to 1.6.
Personally I think there are two primary reason keeping people from using drinks over food.
1) A lot of important things like damage, ultimates, shield absorption, class skills, etc scale off of the over all pool size. In contrast the only things scaling off recovery are a few low percentage passive traits via armor, one or two champion skills, and maybe a class skill or two.
2) Health is extremely important. No health comes with drinks, only health recovery. All the recovery stats in the world don't help you if you get one shotted by a boss or enemy. The squishier classes in lighter armor that focus more on their resource pool often need the extra health from food in order to take the bigger hits.
While having enough recovery to keep resources sustained is great, the above two reasons seems to me to be the biggest, though likely not the only factor involved.
Suggestions:
These are meant to be taken independently from one other, not all together.
1) Drop the recovery rates on food to 30% of their current value and let people use it in conjunction with food. This will ensure people will always want to use both.
2) Keep the recovery rates the same and add some Max Health onto drinks as well. Not to the same degree as food, but enough provide some extra health buffer for the squishy people looking to survive a one shot attack.
3) Increase the recovery on drinks by about 50%. Right now the values are nowhere near enough to draw people away from all the advantages of the max stats.
Anyway, hope you take it into consideration. Thanks.