My wife and I were contemplating this, and realized that neither of us had heard of or could find research relating to actual digestive efficiency and whether it varies among people. She recommended asking here, of course!
I wonder, do any Dopers have light to shed on the question of whether and to what extent some people digest and take in more calories from a given food item? That is to say, if Person A eats a 300 calorie hot dog and Person B eats an identical 300 calorie hot dog, are there natural, genetic factors (besides disease*) that might lead A’s body to just take in 150 calories from consumption through digestion to elimination while B’s body takes in 280 calories?
To clarify:
I certainly understand that metabolic rates differ, and I’m not wondering about how people vary in their natural inclination to burn off calories that are already absorbed or stored as fat.
Similarly, I’m hoping for information that disregards exercise in relation to burning stored calories, but I would be interested to know whether regular exercise affects absorbed calories, whether by increasing or decreasing digestive efficiency.
From searching previous SD threads, I understand that there’s a difference between digestive efficiency for various foods - I wonder about the difference between various people for a given food.
Much appreciation for any responses! This is not an area where an engineer-turned-law-student has much knowledge.
*PS - For a friend of mine, Crohn’s disease manifested as essentially an inability to absorb food through the digestive tract, so he takes in calories intravenously. I wonder about the variation in relatively healthy person.
Here is a page that has a table of digestibility for various foods, broken down by protein, fats and carbohydrates; in general, carbohydrates are the most efficiently digested and proteins the least, except in animal products (it also appears that a mixed meal improves the digestibility over individual foods). It also notes that people vary much less in digestibility than commonly thought, so the thin person is likely just not eating as much or actually burning more calories (fat people in particular tend to underestimate what they eat). In addition, it says that eating a certain food over a period of time will cause your body to become more efficient at digesting it.
It’s certainly known that there are genetic differences in people in digesting certain substances (just as there are differences in people tasting certain substances.) Violent allergies are just an extreme instance of this.
I would have to guess that there are real differences among people in overall digestive prowess. We all are probably acquainted with people who are very uneasy eaters, and others with proverbial cast-iron stomachs.
Interesting link, Michael63129 - thank you. The idea of individuals digesting specifics foods more effectively after prolonged consumption makes sense, much in the way that it takes time to readjust to a meat diet after years as a vegetarian. I suppose the bacteria that aid in digestion of certain foods grow more numerous when their nutrition source is more readily available. I wonder whether some people are also naturally about to sustain higher populations of these bacteria, or whether calories digested per inch of intestine is different between people (vague memories of public school biology make me think that total intestinal tract length is about the same for a very fat and a very thin person).
Trinopus, allergic reactions or sensitivity to various foods definitely affects our food consumption. However, while I might avoid food that causes me distress due to allergies, does that also imply that I would not be able to extract all of its calories if I could keep it down? Or if spicy food made its way through me quickly because I had trouble with its fieriness, would that suggest that I would absorb fewer calories per unit of food than someone with a cast-iron stomach? I suppose, in that situation, time spent in the digestive tract would matter too, of course.
I did some quick googling and came up with this extensive journal article from Physiological Reviews. It’s over 50 pages before you even get to the references but this paragraph gives you a flavor and is on topic.
edit: note that this is from 2010 and a lot of progress has been made since then.
It’s an interesting question. If digestive efficiency between people does vary, I presume the only way to measure it would be stool analysis? (might explain why there isn’t much data on the matter)
That’s definitely in line with what I was looking for - thank you! It seems the paper does correlate diet-induced obesity with increased gut flora populations, suggesting that a person can break down food more efficiently if they’re already overweight. I’ll have to skim the references later and see what else has been written.
Bldysabba, good point - I would not want to do that research! Especially since it would seem to require complete intake and well, output, measurements over a number of days to account for the time delay of the digestive tract…I doubt I’d sign up to be a research subject either.
As a biologist, I would say that any trait that you can measure is going to vary between individuals, and further, that this statement is so trivial and obviously true that it can simply be asserted without evidence. Now, the real question is how large this variation is within a population.
As an anecdote, I’ll offer myself to be on the low end of the spectrum. I lost 30-40 pounds over the last couple of years due to what turned out to be my pancreas spontaneously shriveling up and dying. Because I had virtually no pancreas left, the digestive enzymes it’s supposed to be making weren’t getting into my gut, meaning that a lot of calories were being pooped out instead of absorbed into my body. So my digestion efficiency is much, much lower than the average person’s. I’m now on oral pancreatic enzymes, which I get to take with every meal. Incidentally, to make these, they buy pig pancreases from the local slaughterhouse, isolate the relevant enzymes, and package them in capsule form. They cost (my insurance company) about $900 a month.
Thanks for the info, Smeghead. Don’t lose that insurance!
Now, having achieved a consensus that some people CAN digest more and less efficiently than others, I hope no one will mind if I change the focus of the thread slightly:
Over the years, I’ve read various weight-loss things which purport (with varying degrees of truthiness) to improve one’s metabolism, so that more of the ingested calories will get burnt with the same amount of exercise. Here, I’d like to reverse that. Is there anything a person can do – short of a pancreatectomy! – to change one’s digestion, so that less of the food one eats becomes calories to begin with?
Lift weights. Muscle uses more calories even at rest that fat. Unless it’s brown fat. But I don’t think there much you can do about that. I vaguely recall if you’re willing to make yourself uncomfortably cold for a long period of time you might be able to bump up the ratio of brown to white fat, but don’t blame me if it doesn’t work.
edit: also, exercise raises your metabolism for a substantial period after you’ve finished, so . . . win-win.
Everything you point out would increase metabolism. But that’s not what Keeve was talking about. If I’m not wrong, he was asking if there are any ways to reduce the number of calories available to your metabolism, keeping food intake constant. Keeve - laxatives?
High fiber induces growth of the bacteria that digest the fiber. Consequently more calories are harvested from otherwise indigestable materials. Thing is the stuff it is broken into does all kinds of good stuff including sending messages to centers that regulate appetite and metabolism with the result of less input and more calories burned, often more than offsetting the extra calories extracted. They also have anti-inflammatory effects which are good to have.
So you could avoid most fiber foods and thereby extract less energy from the fiber you do eat. But it would cause more harm than good.
I just came across this which ties for being both interesting and disgusting.
It seems that being infected with roundworms causes a host of beneficial metabolic changes. This was discovered by virtue of the fact that as the rate of infection in developing countries has declined, autoimmune disorders have increased.
Essentially, that’s what metabolic/bariatric surgery does. The two most commonly done forms of metabolic surgery, the RNY/gastric bypass and the Duodenal Switch, bypass the upper part of the small intestine and divert pancreatic enzymes so that ‘normal’ digestion only occurs in a limited, lower part of the small intestine. I had the DS 9+ years ago, and it’s estimated (I personally have never been tested, but studies have been done) that I only absorb about 50% of the protein I eat, about 60% of the complex carbs, and about 20% of the fats. I do still—unfortunately!—absorb nearly 100% of simple carbs, like sugar and white flour.
A clarification - The Roux-en-Y gastric bypass (RYGB), which accounts for the majority of bariatric surgeries done in the United States, is a primarily restrictive procedure. A very small portion of the proximal intestine is bypassed. Malabsorption is not considered its prime mechanism of action. Changes in messengers from the gut to the brain and other locations are a major factor. Possibly altered gut flora are. But shortened gut and consequent malabsorption is not a prime part of RYGB. The more primary malabsorptive procedures (such as biliopancreatic diversion with or without duodenal switch) are infrequently done in the United States.
I’m serious. I read the first page, which is online.
No follow-up since 1925?
Plus, if the topic is not studied further, physical anthropology and medicine will not only suffer from the paucity of simple splanchnometrical data, obviously key in splanchnological studies, as well as denying further appearances in print of the words “splanchnometry” and “splanchnological.”
What the hell? Is that true?