Colnago Mixte

Has anyone ever studied the variability of caloric absorption rates in humans? What I mean by that is, foods are assigned a calorie count, let's say a double quarter pounder with cheese is 750 calories. But just because there's 750 calories in that burger, doesn't necessarily mean every person's body will actually absorb every one of those 750 calories, does it?

Sure, if someone hasn't eaten for a week and is totally famished and eats that burger, it seems likely that all or nearly all of the calories from the burger would be absorbed. The body needs those calories badly. But what if the same person eating it had already eaten 4 huge meals earlier in the day, and had no appetite, but choked it down anyway. In that situation, you would think the body would have some sort of mechanism to just push food through the guy rather quickly, while doing only a minimal amount of digestion and absorption, since the calories were not needed at that time.

If such a phenomenon exists, wouldn't harnessing this effect and fooling the body be a great way for people to lose weight? Just thinking aloud here.

squirtdad

pretty sure the effect that evolution has built in is: If you have and abundance of food, eat it, turn it to fat so it can be used when you have no food. The body is not going to waste calories because you have no appetite....

DrIsotope

Yep, the body is a bioengine, it isn't just going to dump "unburned fuel" because it doesn't need it. It's gonna store it. That's why the rule of thumb states that 3,500kcal per week above what you need for your BMR + activity = 1lb of weight gain.

This is how people get so big that they need surgery to combat it. They're taking in +10,000kcal a day and not moving. They've basically turned their bodies into fat storage devices.

Colnago Mixte

Something like pure sugar, or pure animal fat, sure I can see that being absorbed quickly and easily by the body. But what about plant material like raw or lightly cooked vegetables?

I'm sure that once the gut churns that around long enough, it reaches a point where there are probably more calories that could be extracted during the next 12 hours, but it at some the gut decides, "Hey, here comes a chocolate milkshake! Why waste time on those raw Brussels Sprouts, let's dump that load and start on this one."

I know horse and cow dung was eaten, and seeds picked out of it by starving people during WWII, so apparently animals leave unused calories behind in their waste, so why not humans?

DrIsotope

Because grazing animals (ruminants) have horrible inefficient digestive systems. Rabbits eat their own poop because the system rockets the food through so fast they don't get everything out of it. Cows have multi-chambered stomachs, and chew cud, so they can maximize the energy they get from eating grasses-- aaaand their intestines are over a hundred feet long. Grass is super low cal, basically.

Also, vegetables are really quite low in calories, because it's mostly all indigestible fiber. That's how a whole Steamfresh bag of green beans is like 60kcal. Celery is negative gain-- it takes more energy to digest it than it has in it.

Humans are pretty good at pulling nutrient out of food, because we're omnivores.

Milton Keynes

That's not quite how the human digestive system works. It's going to digest both the veggies and the milkshake, and put that energy (sugar) into the bloodstream. What doesn't get used gets stored as fat. True, sometimes we don't fully digest things (not meaning to be gross here, but think of corn or peanuts in feces) but for the most part the amount of calories you eat is the amount of calories you absorb. And if there's an energy surplus your body will store it as fat. Now some people might have a faster metabolism than others, and your metabolism will change over time, but it still comes down to calories in vs. calories burned.

rgconner

I am pretty sure every calorie I eat not only makes it into the system, it finds 2 or 3 buddies to come along for the ride

DrIsotope

prathmann

There can be some minor amounts that are not digested - like the occasional kernel of corn that makes it through intact. But food that's been properly chewed will be used quite efficiently unless there's some major digestive upset resulting in symptoms like vomiting or diarrhea.

Colnago Mixte

I always wonder what additional digestion and absorption of calories and nutrients takes place when digested matter sits in the large intestine for an extra day, or two or even three. There must be a reason why the body sometimes decides to hang on certain meals longer, additional absorption of something would make sense.

JLDickmon

Your body will absorb all calories you take in. It will use the simple carbs (starches) to make fat, the "slower burning" complex foods for fuel. But it will absorb everything. That's why ketogenic (Atkins, Keto) diets are so popular. With the drastic reduction in starches, it triggers the body to begin consuming it's fat stores. When coupled with an increase in physical activity, the fat stores are burned at an increased rate.

One thing I learned yesterday.. the joint supplement I take? Chock full of carbohydrates.
Time to find a different way to not become the friggin' Tin Woodsman.

raria

To which I'll add the related questions

Is there an accurate method to estimate how many calories we need *after* which the first of the 3500 calories is counted?

How long before the excess calories get converted to fat?

Colnago Mixte

If human stools burn, would that not indicate there is still some food value in them still left to be extracted?

I just have difficulty believing the human body always, and without exception, absorbs every last single calorie we consume.

I thought things like diarrhea interfered with the absorption process, and for that reason, people suffering from this condition can become malnourished.

starkmojo

When it comes to calories I assume that every single one that enters my body is absorbed and add 10% for calories I forgot to log. My daily Intake is just over 3000 calories resting and I shoot for 2700. Usually I end up somewhere in between.

I also assume that I burn half the calories that the workout says it burned. Right now I am performing 5-7 hours a week of high heart rate bicycling along with the normal physical activity of owning 15 acres on a hillside.

I figure if I am wrong I will just lose weight a little faster; but if I am right I will lose weight on schedule.

After 109 days I have lost 32 lbs; My goal in this time frame was 28. So I overshot a little but not by much.

raria

You've got way too much time on your hands ... thinking about crap (literally) all the time :-) Crap being burnt, people picking through crap etc.

jsigone

eat, sleep. ride your bike

repeat often

DrIsotope

Some of the things we eat are indigestible-- it's called fiber. That's why a whole 12oz Steamfresh bag of broccoli has about 120kcal. Most of that just becomes bowl filler. Fiber burns great. Trees are pretty much fiber.

And yes, under extreme circumstances, you will shed calories that cannot be absorbed-- but this occurs when say you've put so much sugar into your system that your body cannot actively handle it, so it first tries getting rid of it in the urine or feces, and if that's not quick enough, you just go for the quick refund (back from whence it came!) Illness is a whole different issue-- the body thinks it's being poisoned, so it initiates the fire sale-- everything must go. As a somewhat long-term sufferer of diverticulitis, I know exactly how that goes. Sure, I can lose 15lbs in less than 24 hours just by swallowing a handful of cashews... but I wouldn't recommend it.

So yes, there can be extenuating circumstances. But if you're sitting on the couch eating Krispy Kremes, it's all getting stored.

KraneXL

The body absorbs it all, although mechanically digestion is a very inefficient process. Still, as mentioned, it takes what it needs for maintenance and upkeep and stores the rest as fat. You fat stores represent the amount of calorie intake beyond what is necessary.

This is why carbs get a bad rap. Carbs aren't inherently bad for you, its just that they're so easy to digest and move through your system. You could literally eat carbs continuously without feeling totally full.

Milton Keynes

Caloric burn is not exactly the same as a fire burning. Paper and wood burn, but they have little to no nutritional value. Our bodies take nutrition out of our food and either burn it for fuel or store it, and the fiber that's left gets sent out as waste.

At any rate, if you're trying to lose weight the last thing you want to do is convince yourself that all the calories you eat don't get absorbed by your body. If anything, you should overestimate the amount of calories you eat and underestimate the number of calories you burn. If you think, "Ah, I can eat a couple of donuts since my body won't absorb ALL those calories" then you're sabotaging yourself.

KraneXL

Far from it actually. One is molecular and the other chemical (inefficient). In addition there are animals/insects that feed on dung so you can see there's still a lot of energy still left in it after digestion

One more thing, getting absorbed and getting utilize may be though of differently. You body may absorb all the calories you eat (to its biological limit) but may not utilize all of those calories as building blocks or useful energy. That growing layer of fat is one indication of all the leftovers.

Colnago Mixte

So everyone seems to be saying that, if I have a mouthful of brown rice, it makes absolutely no difference if I even chew it, every last single calorie in it is gonna be absorbed anyway, so why bother? Heck, why even cook it if that's the case?

From a psychological perspective, I agree wholeheartedly. I'm just wondering, from a physiological perspective, if the body is so damned efficient at converting food, into fat or energy, why we even chew our food, or cook it for that matter.


I suspect the body is not as efficient as people believe.

KraneXL

Because you have to keep in mind the mastication (chewing) is a part of digestion. Therefore, you can't expect it all to be absorbed if you leave out this vital part of the process.

The same goes for cooking: Human digestion cannot break down many (uncooked) complex molecules. The heat (from cooking) is first necessary to convert them into a less complex form the human body can use.This supposition in correct. Relatively speaking, human digestion is highly inefficient.