I'm struggling to think of a way you could use "the category for food" in good written English. I guess you could say something like, "There are five categories of goods which contribute to the consumer price index ... The category for food ..." but I would say that "category" is redundant in this case. It could mean "the category of which food is a part" but that doesn't really fit the context. "The category of food" would be correct, but clumsy. I think this is a classic example of bad business English. I would just say, "Food inflation, which accounts for half the consumer price index, hit 8.4%".