Why does a giant surplus in calories result in immediate strength gains?

Question

I notice that days where I don't eat much, I sometimes fail to get up big lifts with weights.

On days when I sometimes get big surpluses, such as big feasts/etc., I feel powered and like there's lots of more driving force/energy in completing lifts. It's like a big surplus gives you more power.

Is there any explanation for this? Is this why a lot of heavy/obese people can get some big weights moving (like perhaps bench, deadlifts, presses, etc.), despite them not having too much training/etc.?

It's like there's a correlation between intake and outward energy from the foods/etc.

Answer 1

Glycogen. Glycogen is stored glucose that your muscles use to move explosively. Moving heavy weights requires a lot of energy to be expended really fast. Your muscles use the stored glycogen to get that energy. You deplete it throughout the day, and you won't replenish it if you don't eat. Then you don't have enough when you workout, and you feel exhausted. When you have a big feast, you replenish the glycogen and then use it in the workout. It's equivalent to "carb-loading" in the running world.

Being heavy/obese doesn't necessarily equate to being stronger. There's actually a question on this forum that deals with that topic in much greater detail than I'll ever be able to answer. I can't for the life of me find it right now. Though, a more heavyset person is more likely to have topped out glycogen stores simply because they would typically eat beyond their needs. They would experience the same phenomenon you are describing now.