My friend Ron Allan forwards a lot of interesting material to me, and I acknowledge him as the source of the following two slivers of good advice:
Dietary: “Eat what grandma used to eat.”
Life style: “Exertion and exercise, like grandpa used to do.”
That’s not an either/or thing, by the way. If you eat dripping sandwiches and treacle pudding, as many grandmas did not so long ago, you need to do 10 hours of hard physical labour six days a week.
StroppyGit 
I ate prodigious amounts of food when I was young. Teenage friends with similarly “hollow legs” shook their heads at the amount I consumed. But I was never overweight. Why?
I believe the identity for energy balance is:
Energy in = energy burnt (used) + energy stored (fat) + energy expelled (* )
I doubt that even 10 hours a day of exercise would have burnt all the energy that went down my throat. My explanation for remaining trim is that my active life style told my body not to carry excess weight. Accordingly, my body expelled more of the energy I ate. (What a waste! Waist?) Had I been a sedentary soul, like today’s “gamers”, I expect I would have been fat if I’d not cut back on my food intake.
Am I talking about the phenomenon that people loosely term “metabolism” or “metabolic rate”?
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