But assuming you haven't been on the shitter, and haven't been exercising and sweating profusely, then you will weight exactly the same as when you ate UNTIL you visit the bathroom.
Just because your food is digested doesn't magically mean it weighs less. Conservation of mass. Unless of course, mass is given off with respiration? I don't know

I finished Bio in year 11, I'm looking at it from a Physics POV.
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Ooh, I got a sexy ex-staff title!