Chocobo food works with % grade 1 1%, grade 2 2% grade 3 3%.
When you feed it see that you can get a random bonus stats, but isnt really random its % round up. If you chocobo max stat is 100 doenst matter it always going to be 1 point using grade 1 food.

But if it is 110 to 190 you can get 2 points instead of 1, so save your food if you only get 1 point stats, if his max stat is 200 doesnt matter it alwayts going to be 2 points using grade 1 food...