# How quickly can the human body absorb fat from food? **URL:** \ **Category:** Factual Questions\ **Created:** [May 17, 2010, 9:59pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820 "2010-05-17T21:59:53Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [May 17, 2010, 9:59pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/1 "2010-05-17T21:59:53Z")
So, was talking to a co-worker the other day, and he proposed a theory that if you ate an entire pizza at once, you could basically lemming-rush your digestive system and not absorb all of the fat (and other content) of the pizza before it passed through the body. This was contrasted to eating the pizza one or two slices a night for a week, when your body could more easily take it down in, well, pieces. Any truth to this theory, or can my body quite effectively take down an entire large pepperoni pizza from Papa Johns in one pass and absorb all of the fat to be deposited on my ass? ---
**Author:** ![GilaB](https://avatars.discourse-cdn.com/v4/letter/g/8e7dd6/32.png) [@GilaB](https://boards.straightdope.com/u/GilaB)\ **Post date:** [May 18, 2010, 3:08am UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/2 "2010-05-18T03:08:09Z")
Your body can very effectively absorb huge amounts of fat. If you eat a pizza in one sitting, do you see any oil/grease floating in the toilet when you poop the next day? If not, it was absorbed by your system. There’s a diet drug that blocks your body from absorbing fat (orlistat/Xenical), and if someone taking the drug eats a lot of fat, not only do they see fat in the toilet along with their other wastes, they can actually have explosive, uncontrollable diarrhea. Presumably, if you had unabsorbed fat in your feces, you’d know about it. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [May 18, 2010, 3:31am UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/3 "2010-05-18T03:31:08Z")
I love his theory, but the absorption of nutrients happens in the intestines, not the stomach and there’s more than enough time to pull out the fat over the day or two the food makes it’s way through you. In fact, I’m tempted to think that challenging the body with a massive caloric intake bomb is going to cause more of the excess calories to be stored as fat,not less, as the body will not be able to burn the food efficiently, and physiologically your appetite is likely to go back online the next day, even though you still have massive overload of calories in your system. ---
**Author:** ![Shmendrik](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shmendrik](https://boards.straightdope.com/u/Shmendrik)\ **Post date:** [May 18, 2010, 4:58am UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/4 "2010-05-18T04:58:34Z")
Let’s talk about the crust for a second. Your digestive system is incredibly efficient at absorbing carbohydrates, and can absorb 20 pounds of sugar in one day. I’m not sure about the limit for fat absorption, but I doubt it would be overwhelmed by a single pizza. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [May 18, 2010, 6:03am UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/5 "2010-05-18T06:03:36Z")
> [@Shmendrik](#): > > Let’s talk about the crust for a second. Your digestive system is incredibly efficient at absorbing carbohydrates, and can absorb 20 pounds of sugar in one day. I’m not sure about the limit for fat absorption, but I doubt it would be overwhelmed by a single pizza. Re the 20 lbs of sugar in a day do you have a cite for this claim? ---
**Author:** ![Shmendrik](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shmendrik](https://boards.straightdope.com/u/Shmendrik)\ **Post date:** [May 18, 2010, 6:54am UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/6 "2010-05-18T06:54:18Z")
> [@astro](#): > > Re the 20 lbs of sugar in a day do you have a cite for this claim? Sort of. It’s in the notes from a medical physiology course I took. Unfortunately, the professor doesn’t give a source, and some googling [suggests](http://www.edulife.com.br/dados%5CArtigos%5CNutricao%5CNutricao%20Esportiva%20e%20Suplementacao%5CCHO%20intake%20in%20sport.pdf) a figure closer to 5.5 lbs/day. Still enough for several pizza crusts, but not quite as impressive. I emailed the professor to ask for his source. ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [May 18, 2010, 12:07pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/7 "2010-05-18T12:07:19Z")
I recall a study relating to bulimea, where it was shown that purging with laxatives does not prevent significant calorie absorption. So even if high-calorie food passes through your intestine very rapidly, you still absorb the calories (though you’ll miss out on various other nutrients). I imagine the same is true if you eat an entire pizza – no way you’re going to completely overwhelm your digestive tract, to the point that it cannot absorb more fat. ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [May 18, 2010, 12:21pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/8 "2010-05-18T12:21:01Z")
> [@astro](#): > > Re the 20 lbs of sugar in a day do you have a cite for this claim? Fun story, he won a bet that way… (joke) 😃 ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 18, 2010, 1:52pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/9 "2010-05-18T13:52:45Z")
> [@lazybratsche](#): > > I recall a study relating to bulimea, where it was shown that purging with laxatives does not prevent significant calorie absorption. [This one](http://www.ncbi.nlm.nih.gov/pubmed/6190422), no? I actually cited it fairly recently - [here](http://boards.straightdope.com/sdmb/showthread.php?t=557314). ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [May 18, 2010, 2:23pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/10 "2010-05-18T14:23:41Z")
> [@KarlGauss](#): > > [This one](http://www.ncbi.nlm.nih.gov/pubmed/6190422), no? I actually cited it fairly recently - [here](http://boards.straightdope.com/sdmb/showthread.php?t=557314). Yep, that’s the one, and your post was probably where I saw it first. But early this morning my pubmed-fu wasn’t good enough to find the actual cite… ah well, time to caffeinate. ---
**Author:** ![Shmendrik](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shmendrik](https://boards.straightdope.com/u/Shmendrik)\ **Post date:** [May 18, 2010, 3:58pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/11 "2010-05-18T15:58:17Z")
> [@lazybratsche](#): > > I recall a study relating to bulimea, where it was shown that purging with laxatives does not prevent significant calorie absorption. So even if high-calorie food passes through your intestine very rapidly, you still absorb the calories (though you’ll miss out on various other nutrients). I imagine the same is true if you eat an entire pizza – no way you’re going to completely overwhelm your digestive tract, to the point that it cannot absorb more fat. I assume you know this, but just to be nitpicky: Your intestines don’t absorb calories, since calories are an abstract concept representing the energy your body can use from various nutrients, such as carbohydrates, fats, and proteins. ---
**Author:** ![Shmendrik](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shmendrik](https://boards.straightdope.com/u/Shmendrik)\ **Post date:** [May 18, 2010, 6:15pm UTC](https://boards.straightdope.com/t/how-quickly-can-the-human-body-absorb-fat-from-food/539820/12 "2010-05-18T18:15:57Z")
> [@Shmendrik](#): > > Sort of. It’s in the notes from a medical physiology course I took. Unfortunately, the professor doesn’t give a source, and some googling [suggests](http://www.edulife.com.br/dados%5CArtigos%5CNutricao%5CNutricao%20Esportiva%20e%20Suplementacao%5CCHO%20intake%20in%20sport.pdf) a figure closer to 5.5 lbs/day. Still enough for several pizza crusts, but not quite as impressive. I emailed the professor to ask for his source. Ok, here’s what he had to say: > [@](#): > > I hope you don’t have too much money riding on this. The data is obtained from extrapolation of data from Am. J. Clin. Nutr. 1989 vol 49: 1247. > > At max glucose solutions tested, uptake is ~30 mmol/10 cm/hr. Assuming a small intestinal length of ~ 625cm = 1,875mmol/hr = 45,000 mmol/24hrs 1mmol glucose = 180 mg= 8.1kg glucose /intestine/day ~18 lbs. > > Hope this helps. Of course this is more theoretical than practical, but it does show the remarkable capacity for glucose uptake. I suspect the practical limit is probably closer to 5 pounds per day. OTOH, looking at glucose absorption alone should give a low figure, since other carbohydrates use different transporters to cross the intestinal epithelium.