when i was growing up (in the eighties...wow) I remember friends being OBSESSED with calories, counting calories, eating things that were lower in calories, and as the years went by, scientists started to claim counting fat grams was key, so everyone i know went nuts eating low fat in the nineties.

Ultimately, it's all about balance. Don't eat any food group excessively, exercise regularly, and if you are exercising and training a fair bit, remember to give your body a chance to rest.