Jerry Rice -- I Always Played On an Empty Stomach

Forget protein bars or power shakes or a pasta carb-loading ... Jerry Rice tells TMZ Sports he used to take the field on an EMPTY STOMACH.

Seriously, kinda crazy considering how dominant he was -- but #80 swears he never scarfed down any food before a game.

Rice was just out in NYC -- nicest guy ever btw -- and we chatted about food, TD dances and hecklers.