Food does not say stack +2. It does say max +2, but that does NOT mean you can stack food. Rather, it's a limit on how high the buff will work. So, for example, if a piece of food says it gives +25% Vitality (max +5), that means you get a bonus of 1/4th your vitality, up to +5, which occurs at 20 Vitality. Past that, the food only ever gives +5 Vitality, even if your base is 500. This system means you must use low level food at low levels, as higher level food has lower percentages but higher caps.