From food to weight – how long does it take?

I have a friend who is obsessed with the number on her scale in the morning and thinks it’s directly related to whatever she ate the day before. I feel like I remember hearing it takes longer than that. Logically, there are other biological functions that play a role – water weight, hormones, contents in bowels, etc. From your research, what would you estimate is the time it takes to go from the lips to the hips?