But I don't believe this is for older people. Dietary needs change.
The deal is that you have to stay warm in the winter when you are just standing there. Carbs and water do the trick, but you have to ease off in the summer, or skinny foreigners will talk about you in foreign languages and snicker.
At the risk of over-seasoning the pot, I will add my wisdom.
Protein is wonderful, but it must be very fresh. If it isn't sitting in a pool of its own blood and doesn't scream when you stick in the fork, it's not even food.
Vegetables are a must when you're having company for dinner and want to make the plate look colorful. If you own tropical pet birds, they will appreciate the leftovers.
Carbohydrates must only be eaten when decently dressed with things like marzipan, sacher tort chocolate, creamed rum sauce and the like.
Fat is the lubricant in your diet that makes all the parts work smoothly together. There is a reason they say, "It's better with butter," just as there's a reason I don't want the butcher to slice the fat off my steak. If you add enough melted asiago cheese to finely minced vegetables, they actually become tolerable.
Exercise -- something's gonna get you, no matter what you do.