The food pyramid is meant to insure that people who use it as a guide will get the right amounts of vitamins and minerals, fiber, protein, etc. and not gain weight in the process.
In the end, calories for the day can be apportioned any way you want them. And whatever works for you, works for you. I have heard the 'I lost weight and then I gained, doing the same thing' applied to every diet (including low-carb diets). You just adjust, adjust, adjust. For one thing, your body is not stuck in time. You're getting older, and your hormonal profile (for a woman, that's an entirely different thing...) is changing with every bit of aging, too.