How many calories can you eat in a day?

August 26, 2007 6:53 PM

What's the maximum number of calories a human can digest in a day?

Is there a limit to how many calories the human body can digest in a day? If so, what is it? What happens if you eat more than this limit?

This is to settle a bet with a friend.

posted by christonabike to health (17 comments total)

I am sure there is some scientific answer based on weight, size, etc, but watching the Coney Island Hot Dog eating contest, 60+ dogs in a day is testing that limit.
posted by JohnnyGunn at 7:06 PM on August 26, 2007

I think what you're looking for is the LD50 of cooking oil or fat multiplied by the average weight of an adult (180lbs for an adult man) multiplied by 9 kcal per gram.

That would give you the average maximum number of calories that an adult man would be able to ingest via the most efficient means (largest number of calories per weight).
posted by bshort at 7:07 PM on August 26, 2007 [2 favorites]

I was watching some show about the morbidly obese at Brookhaven clinic in New York, and it was said that some of those people were doing 25-30 Thousand calories or more per day.

I would suppose that they were probably pretty close to the limit of human consumptive ability. These were people who, for whatever reason, would eat as much as they could as often as they could.
posted by Pogo_Fuzzybutt at 7:08 PM on August 26, 2007

During training and during competition in the Tour de France, riders go through upwards of 6000 calories per day, and unlike PF's example they do not get fat. They really are using that much energy on an ongoing basis.

(This page says "5900 calories per day average, 9000 max". This one says "6000-7000 calories per day".)
posted by Steven C. Den Beste at 7:15 PM on August 26, 2007

I'd suspect it's feasible to do around 25-30k dietary calories per day. When I rode a loaded touring bike cross-country, covering around 100 miles a day, I was consuming maybe 7,000-8,000 calories each day. I understand Tour de France riders eat around 10,000 a day.

I know of some people who were going for a speed record on the Continental Divide trail (a mostly off-road bike route from Mexico to Canada). They did the whole thing in 11 days and were drinking vegetable oil pretty much the whole time -- it's the most densely caloric thing a human being can easily consume. I'd guess you could get up around 20k calories/day pretty easily if you wanted to drink vegetable oil.
posted by killdevil at 7:18 PM on August 26, 2007

I think the question needs to be reframed--are you asking how many calories can be consumed, how many calories can be utilized(expended), or how many calories can be stored in one day. The latter two depend on expenditure. I believe calories are not digested but rather manufactured and stored.
posted by rmhsinc at 7:22 PM on August 26, 2007

One Betty White cheesecake clocks in at over 5k calories. I could probably eat 3 of those in one sitting, maybe 15-20 in a day. Even if I just manage 10, that's 50k calories. I see that as completely doable. I'm sure the number is in the 6 digits.
posted by damn dirty ape at 7:36 PM on August 26, 2007 [1 favorite]

I think we need to consider the difference between calories consumed and calories absorbed. As an avid consumer of beer, I'm pretty sure that the quantity of calories I consume does not equal the quantity of calories I absorb, or otherwise I'd be a lot more overweight than I am. Unless I'm mistaken, food calories are calculated as a theoretical maximum based on the physical energy content of the foodstuff. I strongly suspect this doesn't equal the biologically available energy. Put another way, every kCal ingested doesn't equal a kCal absorbed.
posted by mollweide at 7:47 PM on August 26, 2007

...some of those people were doing 25-30 Thousand calories or more per day.

Sounds like heaven. Must be expensive, though.

I know 3500 calories=1 lb weight gain, but I agree with mollweide: calories ingested doesn't equal calories absorbed. When we produce feces, I'm sure it's not calorie-free.
posted by HotPatatta at 9:08 PM on August 26, 2007

To help clarify: no matter how much you consume, you can only digest so many calories. The rest pass through your system "undigested". The poster wants to know how many you can actually digest, not merely consume.
posted by hermitosis at 9:09 PM on August 26, 2007

As others have said, once you reach a certain intake of calories, the rest will go right through you. So, are you asking how many calories I could stuff into my gullet, or how many calories my body could absorb? The answers will be quite far apart.

Off the top of my head, I'd suspect that the limiting factor for absorption would be enzymatic production. Large complex molecules aren't easily absorbed through the intestinal wall, so you need enzymes to break things down into small molecules (starches -> simple sugars, proteins -> amino acids, etc) If your pancreas (et. al) can't keep up, then much of that will simply slide right through the digestive tract. (and make excellent fodder for the 10 trillion or so bacteria living in your gut)
posted by chrisamiller at 9:14 PM on August 26, 2007

The TdF guys really are metabolizing their 6-8 thousand.
posted by Steven C. Den Beste at 9:20 PM on August 26, 2007

I read in National Geographic Adeventure (several months ago) about Arctic explorers who had to maintain 7k + calories each day. They did it by drinking a liter of olive oil (in addition to other stuff of course). Crazy Norwegians.
posted by special-k at 10:50 PM on August 26, 2007

Apparently a liter of olive oil has about 9000 calories, so those arctic guys weren't going about it very efficiently, it would seem.

I do remember reading about the tour de france guys and their 10000 Calories, and I seem to remember that it was their energy intake that was considered to be the limiting factor in their abilities. If that's true, that may be your answer (with the caveat that there may be methods of increasing it (like getting extremely fat) that are incompatible with being an athlete).
posted by alexei at 1:34 AM on August 27, 2007

i don't think there's a caloric limit--i think it's more of a question of volume.

i mean, assuming you had the wilpower, you could eat a stomachful of lard or a stomachful of lettuce. same volume, very different number of calories.
posted by thinkingwoman at 4:15 AM on August 27, 2007

I have no citation, but I read the Tour de France guys go to the extent of inserting a drip (or was it a feeding tube?) at night so they can absorb more calories while they sleep.
If that is true, it would seem the 6-7k calories is indeed a metabolic limit.
This has been discussed on MeFi before
posted by bystander at 6:39 AM on August 27, 2007

Although it may not live up to 30k-a-day mentioned above, this man (previously) apparently consumed 7,000 calories a day just in beer. Add in food and other liquor....

'Course Msr Le Giant was hardly "average".
posted by elendil71 at 10:39 AM on August 27, 2007