Two key concepts emerged. For example, a plain baked potato or a plate of rice and beans provide much more eating satisfaction, calorie for calorie, than French fries or T-bone steak. My Dad used to say he never let being full stop him from eating more. I'm the same way. Like the comic strip character Hagar, my only limit is that I never eat anything I can't reach.
Many masters are the same way.
Masters are careful about portion sizes. Most of them have learned from long experience to gauge portion size by eye. But if their weight starts creeping up they go back to weighing and measuring portions, especially foods which are higher in calories, such as meat or dairy products. When I'm preparing for photos, as I am at this writing, I weigh or measure portions and write everything down in my training diary. This gives me a handle on how much I'm eating and allows me to adjust my diet as necessary to achieve peak condition.