Suppose at dinnertime, I pig out, and eat three pounds worth of food. Naturally, if I get on a scale afterwards, I will weight three pounds heavier than before. How long will it take for that three pounds of fine cuisine to pass through my system and out of my bowels (assuming normal digestion and whatnot)?
Similarly, if I had guzzled a half-gallon’s worth of water (approximately 4.15 lbs., IIRC), how long will it take for that half-gallon to get passed out as urine?
Not all the cuisine will be passed through your digestive system. Some of it will be digested. How fast the undigested portion will pass will depend upon what the food contained. Fiber will expedite the passing. It will also depend upon on the health of your peristalsis, which depends, in part, on your abdominal musculature.
Similarly, not all the water will pass as urine. Some will be absorbed. In addition, other foods other than water contain water. Most foods contain some water, and veggies contain a lot. The bladder can normally hold about 400 ml of water and you get the urge to pass some when it contains about 250 ml.
You have asked a question that is in the major league “It Depends” category.
Liquids pass through the digestive tract very quickly, but most water should be absorbed into the body before it hits the colon. Some conditions can interfere with this, which is how diarrhea forms, but water should get passed on to the bladder in a matter of minutes to hours.
Solid foods depend even more on the conditions under which they are eaten. Different foods are broken down in different places. Digestion begins in the mouth, though only to a small extent. The stomach does a better job of breaking food down to what is called chyme. But most true digestion takes place in the small intestine, where hundreds of enzymes digest - break down into amino acids, simple sugars, and fatty acids - the food. Again, the liquid content as well as the solids composition will affect this. Food normally passes very slowly through the small intestine so that all the molecules have a chance to be hit on by the enzymes. Some enzymes are released into the chyme; others are produced at the brush border of the villi that form the inside surface of the intestine so that the molecule has to attach itself to the surface for the enzyme to crack it.
Think of an assembly line at a recycling plant. All sorts of paper, plastics, cans and bottles are tossed in at the beginning. And each one has to be picked out and sorted into the right slot before the end, but all the non-recyclable materials have to be left on the belt to be discarded. This is obviously easier if it’s all bottles or all paper rather than a mix.
I’ve seen the “average” time from mouth to anus at around ten hours, but that number has a huge amount of variation in it. Rapid transit, irritable bowel syndrome, and other intestinal problems can speed the food through without proper breakdown and digestion. OTOH, food can sometimes take a day or two to complete the journey. Undigested lactose can be fermented by bacteria in the colon for up to three days.
Don’t be fooled by needing to defecate immediately after a meal. That’s not the food you’ve just been eating, but a reaction known as the gastrocolic reflex.
No one knows. Every person is different and time will vary from 24/48 hours minimum to as much as several day. You can eat a few charcoal tablets to act as a marker and wait fot them to show up. Ask you Pharmacist about them.
A few to several hours. Ask your Pharacist about a dye marker to detect the first amount.
36 hours, exactly. At least that’s how long it took for the first solids to make the tour after my last pre-colonoscopy total purge.
Your experience is not universal. Bowel transit times have ranged from 5 minutes to 3 weeks or longer.
5 minutes? How on earth would one manage that? Even with no digestion going on, the digestive tract is about 20-30 feet long. It would take me close to that amount of time to manually squeeze a piece of food though a tube that long.
If you want a low-tech marker, eat something really spicy and see how long it is before it feels like you’re passing razor blades.
Thanks for all the replies!
Well, that’s only six feet per minute…
Any beer drinker could have given you average figures for water passing through the system. Start pounding beers at a party, then check to see when your urine goes from its normal shade to Bud Light. 
Have your gallbladder taken out–I think you’d find that five minutes might be a serious overestimation! 
The stardard advice to new mothers is to give the infant a spoonful of chocolate syrup, which will show up as a very dark stain in the stool.
Short bowel syndrome. There are folks out there who, thanks to surgery, have about 15 feet of small intestine and no large intestine to speak of, along with foreshortened stomachs.
Even without surgical restructuring, liquids can pass thru in less time than that if someone has “lead pipe” syndrome. No bowel motility, pour it in the top, it runs out the bottom.
Hyperactive bowels (the gut is really just one long muscular, absorbant tube, after all) can also result in real fast transit time.
I once had a colonoscopy and 6 hrs after I ate I had my first good sized bowel movement. I wonder if this is part of the reason I stay skinny cuZ food literally goes right through me. I generally have 3-4 BMs a day. Tmi I know!
Sometimes even zombies contain useful information. I wonder how common the week+ times are?
When I was in grade school, I typically had one BM a day. But after I stopped growing, and my metabolism started slowing down, the time in between gradually lengthened. For some years now, I generally go 4 or 5 days between BM’s.
I thought the stomach took 20 minutes between “empties.”
FWIW, If I have a tall, cold glass of apple juice, I better be heading to the can by the time I finish it (slight exaggeration).
I have eaten some SPICY food in my life, yet have never, ever felt a burning capsaicin reaction when defecating. It kind of baffled me when younger when people would say they could detect spicy food exiting their body.
Is my butthole made of steel or if there another reason?
I have burped up to 6-8 hours post eating something with a distinct taste or odor, and strongly detected it in that burp.
Test.
Go eat peanuts and corn.
Record time.
Check for said corn and peanuts in your droppings.
Record time.
There’s your answer.