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clop
2009-Jul-30, 08:04 AM
One calorie is 4.184 joules. One kilocalorie is 4.184 KJ.

I've just eaten a 50g Cadbury Dairy Milk chocolate bar. On the wrapper it says that it contains 1115 kJ of energy, or 266 kilocalories (in normal conversation we tend to drop the kilo prefix and say "266 calories").

If I go to the gym and play on the elliptical stepping machine for half an hour it generally tells me that I have expended around that number of calories (it means kilocalories).

My questions are these:

Does the human body absorb all the calories in the food it eats? If not, what fraction does it absorb? i.e. Do I need to step for half an hour to offset the chocolate bar or can I offset it in 10 or 20 minutes?

Will my body absorb a greater fraction of the calories I eat if I'm ravenously hungry?

Will my body absorb a smaller fraction of the calories I eat if I absolutely stuff my face full with mud cake, creme eggs and chips?

What else can make it change?

I guess what I'm trying to say (in a less gross way) is "what is the calorific content of human faeces and what factors affect the value?"

clop

G O R T
2009-Jul-30, 11:10 AM
Not every person has every functional peptide, and so utilization of specific food constituants vary.

Metabolic pathways like liver function vary in the population and are subject to change with health and age.

Intestinal flora do much of the pre-digestion and so the numbers and specific variants of of those flora also affect absorbtion.

Being ravenously hungry would have little effect, but being actually starving increases absorbtion.

Very large meals are frequently evacuated before normal absorbtion occurs.

Gluttony (eating more than needed) eventually causes pervasive metabolic changes like insulin resistance which affect storage efficiency more than absorbtion.

clop
2009-Jul-30, 11:27 AM
Not every person has every functional peptide, and so utilization of specific food constituants vary.

Metabolic pathways like liver function vary in the population and are subject to change with health and age.

Intestinal flora do much of the pre-digestion and so the numbers and specific variants of of those flora also affect absorbtion.

Being ravenously hungry would have little effect, but being actually starving increases absorbtion.

Very large meals are frequently evacuated before normal absorbtion occurs.

Gluttony (eating more than needed) eventually causes pervasive metabolic changes like insulin resistance which affect storage efficiency more than absorbtion.

Thank you, so on average how many of the 266 kc in the chocolate bar do you think I will retain?

G O R T
2009-Jul-30, 12:00 PM
Typically a base would be derived empirically. In lieu of that I can only guess.

If you digest fats normally, I would hazard a guess of 85%.

If you had not eaten for qiute some time before (+12hrs), this would go up.

clop
2009-Jul-30, 12:10 PM
Typically a base would be derived empirically. In lieu of that I can only guess.

If you digest fats normally, I would hazard a guess of 85%.

If you had not eaten for qiute some time before (+12hrs), this would go up.

So when they publish the calorific content of food are they giving us the theoretical absolute maximum based on a person having every functional peptide and not having eaten for two days? Maybe a slimming pill that deactivated the dominant enzymes would be an effective way to lose weight?

clop

G O R T
2009-Jul-30, 12:48 PM
Missing peptides and enzymes cause problems like lactose intolerance and oligosaccharide intolerance. These conditions reduce digestion and absorbtion but frequently cause quite undesirable gastrointestinal effects.

Any simple carbohydrates and simple sugars in food will be absorbed quickly if the intestinal lining is healthy. Not much can be done about this except to limit their inclusion in your diet.

Protiens and complex sugar digestion is affected by gastriintestinal acids, enzymes, and peptides.

Fat digestion is strongly influenced by Pancreatic and Hepatic (liver) secretions like Bile.

The most effective way to lose weight is to reduce caloric intake by replacing some of the bulk of the food with increased fiber content, and reducing the Glycemic Index (http://www.glycemicindex.com/)of your diet in general.

Nick Theodorakis
2009-Jul-30, 02:59 PM
The caloric content of food can be determined by bomb calorimetry, but I doubt that's routinely done for every nutrition facts label you see; rather, I suspect they estimate the caloric content based on the amount of digestible carbs, fats, and protein (and ethanol, I suppose for drinks) per serving and use already calculated values for those. This would, as you suspect, give the maximal possible value. If one wanted to find the fraction of absorbed calories in a clinical setting, one could do bomb calorimetry on the total food fed a test subject, collect the waste over the same period, and do bomb calorimetry of the output, and the difference would be the absorbed calories.

Nick

nauthiz
2009-Jul-30, 09:12 PM
Cooking can also make a difference; the percentage of calories we absorb from raw foodstuffs can be as little as half of the percentage we absorb from the same food when it's cooked.

clop
2009-Jul-30, 10:47 PM
The caloric content of food can be determined by bomb calorimetry, but I doubt that's routinely done for every nutrition facts label you see; rather, I suspect they estimate the caloric content based on the amount of digestible carbs, fats, and protein (and ethanol, I suppose for drinks) per serving and use already calculated values for those. This would, as you suspect, give the maximal possible value. If one wanted to find the fraction of absorbed calories in a clinical setting, one could do bomb calorimetry on the total food fed a test subject, collect the waste over the same period, and do bomb calorimetry of the output, and the difference would be the absorbed calories.

Nick

It's the difference I'm looking for. Or a range of difference. Do we vary from 50% to 100%? Has anyone done a study?

Amber Robot
2009-Jul-30, 11:53 PM
one could do bomb calorimetry on the total food fed a test subject, collect the waste over the same period, and do bomb calorimetry of the output, and the difference would be the absorbed calories.


As I was reading this I was picturing some poor grad student who had to blow up someone's poop for his thesis work.. hehe...

Tucson_Tim
2009-Jul-31, 12:09 AM
Cooking can also make a difference; the percentage of calories we absorb from raw foodstuffs can be as little as half of the percentage we absorb from the same food when it's cooked.

In a similar vein, I remember reading a long time ago that the human body burns more calories attempting to digest raw foods like lettuce (or it may have been celery?) than it obtains from the meager number of calories in those vegetables. Does anyone know if this is true?

BTW, good questions clop.

robross
2009-Jul-31, 12:24 AM
I don't have any study data to support this hypothesis, but I'm quite convinced that in my particular case, my body seems to absorb in the neighborhood of 110% of the calories ingested.


Rob

Tucson_Tim
2009-Jul-31, 01:55 AM
I don't have any study data to support this hypothesis, but I'm quite convinced that in my particular case, my body seems to absorb in the neighborhood of 110% of the calories ingested.


Rob

I think I'm in the 110% bracket too. I think age is part of the equation. The older you get the higher the percentage--at least it seems that way.

Nick Theodorakis
2009-Jul-31, 02:43 AM
It's the difference I'm looking for. Or a range of difference. Do we vary from 50% to 100%? Has anyone done a study?

It's done sometimes as part of a medical study, but usually with patients that may have trouble absorbing nutrients. This paper (http://www.ncbi.nlm.nih.gov/pubmed/19046971), for example, looked at patients with short-bowel syndrome (those who had parts of their intestines removed).

Nick

Gillianren
2009-Jul-31, 03:18 AM
In a similar vein, I remember reading a long time ago that the human body burns more calories attempting to digest raw foods like lettuce (or it may have been celery?) than it obtains from the meager number of calories in those vegetables. Does anyone know if this is true?

Depends on whom you ask, apparently.

http://www.straightdope.com/columns/read/2507/does-chewing-celery-consume-more-calories-than-it-provides

Tobin Dax
2009-Jul-31, 04:14 AM
As I was reading this I was picturing some poor grad student who had to blow up someone's poop for his thesis work.. hehe...
You don't need an explosion, you can just light a match. In high school biology, we took a peanut and burned it to find its caloric content. No explosives were necessarily needed.

Gillianren
2009-Jul-31, 05:17 AM
"Bomb calorimeter," as I understand it, has to do with the fact that it looks like one of those old-fashioned bombs, not because things are actually blown up in it. I could be wrong, though.

mike alexander
2009-Jul-31, 05:24 AM
"Bomb calorimeter," as I understand it, has to do with the fact that it looks like one of those old-fashioned bombs, not because things are actually blown up in it. I could be wrong, though.

That's correct. High pressure hydrogenators are also called bombs.

Ivan Viehoff
2009-Jul-31, 02:27 PM
There was very recently a paper publicised arguing that the bomb calorimetry measure of calorific value of food is inaccurate for the intended purpose. Maybe you can google it, I can't be bothered.

Specifically, the bomb calorimeter will combust things like fibre that actually pass through the body, and proteins that are absorbed but (usually) not fully used for energy. So fibrous food, especially, has fewer absorbed calories than that it says on the label, and also high protein food. Fatty and sugary foods are those that are closest to what it says on the label, though some (especially low melting point) oils are less completely combusted by the body than others, with noted effect on ones waste.

Someone said that cooking things reduces calories. That makes sense, because cooking reduces the fibrousness. But curiously, sometimes cooking things reduces the useful calories. I once read, in a book on the chemistry of food, that if you hold cooked rice at a warm temperature for a period after then end of its normal cooking time, say 10-20mins, it has an internal structural change that results in some of the carbohydrate linking up into so-called "soluble fibre". Interestingly, I prefer the taste of rice that has been left to stand (in its closed cooking pan) for 15 mins or so after the end of the normal cooking time. But starving people should clearly try to eat it as soon as it is cooked.

Ivan Viehoff
2009-Jul-31, 02:30 PM
... 1115 kJ of energy, or 266 kilocalories (in normal conversation we tend to drop the kilo prefix and say "266 calories").
Scientists do the same, but they use a capital C for the Calorie that means kilocalorie.

Ivan Viehoff
2009-Jul-31, 02:38 PM
I think I'm in the 110% bracket too. I think age is part of the equation. The older you get the higher the percentage--at least it seems that way.
Some of the cells in your body are in the form of brown adipose tissue, also known as brown fat, that is effective in converting to heat the excess energy that would otherwise form white fat. It will even consume the white fat you have. Some people have more brown adipose tissue than others - they are the kind that don't put on weight very easily. But we all lose brown adipose tissue as we get older, which is part of the explanation for middle aged spread.

On the New Scientist website today is a news item that scientists have found a way of culturing and then injecting brown adipose cells into mice, and it "takes" and they then get less fat. The research team hopes that this can in future be the basis of a "treatment" for overweight people. I think they said as little as 50-100g of additional brown adipose tissue in an adult human would do a useful job in consuming fat.

clop
2009-Aug-01, 08:00 AM
All very interesting but still I'm wondering - what percentage of the available calories in a bar of chocolate would the average healthy person absorb? Close to 100%? Or much lower?

Lord Jubjub
2009-Aug-02, 01:06 AM
Chocolate bar? Eaten by itself, I think a good estimate is around 95-100%.

nauthiz
2009-Aug-02, 05:42 AM
Yeah, in a chocolate bar pretty much all the calories will be in the form of simple sugars and fat, and they're not not really protected by cell walls or anything like that so the body should have an easy time digesting it very efficiently.

mugaliens
2009-Aug-02, 08:37 AM
Lean mass requires approximately 16 kcal/lb/day for both men and women to sustain it's mass. Thus, determine your %body fat, and your basal metabolic rate is approximately:

BMR = Weight * (1-%body fat) * 16. For me, this comes to around 2,460 food cal per day.

The cool thing is that this works regardless of whatever percentage of calories are absorbed. Naturally, maintaining lean body mass also requires consistant, all around exercise, so one has to add that and one's other daily tasks to the mix to come up with a maintenance caloric intake.

If you want to lose weight, increase exercise moderately (20-30 min aerobics, 2-3x/wk, + light to medium varied weightlifting (think Nautilus) while decreasing food intake moderately (a 25% reduction from your maintenance caloric intake is a good target - no more than 30%).

All the hype about what "type" of caloires is nonsense, except that some foods are known to satiate hunger, long-term, while others are known to accentuate it.