We have billions of complex chemical processes involved in all of this, and know things like "absorption rates of medicine, vitamins, and nutrients" are affected by everything from random vitamins to environmental factors to whatever else.
But body mass, that we have down 100% for-sure, and it's just that simple formula, no variables, no possibility for any other affecting factors. Sure.
Fat tissue is no exception. Your body is only able to make it if you give your body sufficient raw materials to make it.
Similarly, if your body is doing work, it is burning energy. Human bodies are not perpetual motion machines, they exploit energy stored in chemical bonds. You don't get that for free, you get that from the food you eat.
You do not need to fully understand every nook and cranny of a system to examine it from first principles.
What is your proposed mechanism for counting calories in and out for a given person (Note: nutrition labels will 100% fail you here, because of how they are calculating)?
It doesn't matter if they are exact for a given person so long as the labels are consistent. They are sufficiently consistent.
I'm curious - have you tried losing weight, and is this from personal experience? Because I found it trivial by just counting calories and keeping a watch on my weight. I don't doubt that sometimes the calories I absorbed were less or more than what I wrote down, but that doesn't really matter in the long run - they're sufficiently accurate.
You argue this with literally no data, and all available data says the opposite.
The people charged at the FDA with coming up with the mechanism for these labels disagree with you, and have found 30-50% variance for a ton of foods.
"I'm curious - have you tried losing weight, and is this from personal experience? "
I can lose weight fine (and i'm actually at a normal BMI, FWIW :P), and i don't violate the laws of thermodynamics.
However, counting calories from labels was the most useless thing i could ever do.
I literally burned 1500+ calories in exercise a day, and ate less than 1500 calories by nutrition label calculations, and did not lose weight. I tried a variety of different foods/etc. I'm a scientific guy, i have logs of data :P I didn't cheat, kid myself, whatever.
It turns out, for various medical reasons i won't get into, i am not in the "vast majority" for whom these labels are targeted, and so the numbers on them are simply wrong by about 20-30% for me (this is factual, and was actually part of a controlled study). The out calculation was accurate enough (IE the exercise part of it). But as you can imagine, when trying to lose weight, 20-30% in variance matters a lot.
You can argue "i'm outside the norm", but i suspect, based on what i saw, that i am not.
I was not fitbiting or any crazy mechanism to count getting up from the couch as exercise, or counting anything other than the actual exercise calories as "calories burned". Thus, it should have been a significant underestimate due to resting calories burned, etc.
In any case, it was running 5 miles a day, as reported by GPS, at 8:15 pace (which is roughly 120-150 calories per mile, depending who you believe, but i took the low side), and then running 1000 calories on an elliptical (which is about 1-1.5 hours at high resistance and fast pace, depending on pace).
The elliptical i used was one which slightly underestimates calorie count (by about 3%, at least according to two peer-reviewed studies), unlike most, which overestimate (by about 15-20%).
Also, doing that much exercise, you can maintain a calorie deficit (a real deficit of calories absorbed vs. burned) and not lose weight by gaining muscle as fast as you are losing fat (muscle has a lower stored-energy content than fat); you'd need more than just stepping on a scale to distinguish that.
AFAIK, the main reasons that the calorie counts are not accurate for all people is variations in absorption for particular nutrients due to metabolic variations. These variations between people are specific to particular categories of nutrients (some are at the level of macronutrients -- particularly that I've heard of, differences in general fat or carbohydrate metabolism -- some more narrow.)
This would make the top-line calorie counts (or, more precisely, the relationship between top-line calorie counts of different products) inconsistent as well, in that for a person with absorption different than that targeted by the labeling, product A with 500 Cal and product B with 600 Cal might not merely provide different Calorie counts than 500/600 to that person, but product B might provide less Calories than product A, depending on the specific nutrient composition of those calories.
Guys, metabolism is just too complicated for humans to understand, so there's nothing at all I can do about being overweight, it's literally beyond my control
There's got to be some kind of cognitive dissonance or something at play; how else could a rational mind convince itself that the laws of thermodynamics do not apply to the human digestive system?
Or the justifications that say, nutrition labels are not PERFECTLY accurate so it's hopeless from the start. I personally guarantee if you drink one can of Coke a day and eat nothing else, you will lose weight; I don't care whether the nutrition label is perfectly accurate.
I really wouldn't have expected that sort of reaction on this forum ahead of time. It's a bit disappointing.
You have presented literally no evidence to support your argument, which boils down to "it's close enough, if everyone just did hard work and tried harder instead of being fat and lazy, they'd lose weight, and anyone who says otherwise is just being fat and lazy".
I am neither fat nor lazy (I'm actually probably one of the most in-shape adults you'll meet). I can literally prove that your argument is wrong for me.
Instead, what i see is "oh, well, it's sad everyone but me is wrong". With no evidence to back this up.
Now, if your BMR is 2000 and you eat 2100, poor absorption can still cause you to lose weight.
But if your BMR is 2000 and you eat 1000, there is no possible way you can gain weight.
If you know how to gain weight on a calorie deficit, there's a lot of starving people in this world that would love to learn how.
Sure, but both the absorption and the burn rates are affected by other factors.
So calculating calories out is not as simple as looking at a nutrition label.
In fact, it's infinitely more complex: "Instead, the total caloric value is calculated by adding up the calories provided by the energy-containing nutrients: protein, carbohydrate, fat and alcohol. Because carbohydrates contain some fiber that is not digested and utilized by the body, the fiber component is usually subtracted from the total carbohydrate before calculating the calories."
IE note: these are all things that are going to be digested or not digested (and thus, really count or not really count as calories) at different rates in different people.
(Certainly, there is a max value, but this method won't give you that either :P)
Your burn rate doesn't drop below your BMR.
Basically there's lots of variability when you are eating more than your BMR- you could gain weight, or you could not.
But when you eat less than your BMR, you have a calorie deficit. Period. It doesn't matter if your digestion is working well or poorly, or if you exercised or if you didn't. You have a deficit.
As for nutrition labels, I'm not aware of any hidden calories that aren't counted in the label but will be digested. Like I said, humans cannot digest fiber, at all.
There's also a given persons reaction to different macros over time... sugar vs fat vs protein have different chemical reactions in the body, where too much sugar in some will have different affects over time. Some will gain weight, and show signs of metabolic syndrome, others may have the issues, but not outwardly show via weight gain. Others still won't develop diabetes.. and this can be on roughly the same diet.
BMR isn't in and of itself the only measure... while it's true that you will gain/lose weight depending on how many calories you take in/out... but beyond that is what types of mass are gained/lost. Most fat people don't have enough lean muscle once they're over 35-40, which means losing too much muscle (or any) is a detriment. If you start losing more than a sustainable muscle mass, you can actually be worse off. You need to take in a minimal amount of protein to maintain/gain muscle (combined with exercise to promote gaining/maintaining muscle)... with a calorie deficit enough for weight loss, but doesn't cause starvation response and metabolic slowdown.
All of these are definitely variable by person.
Are your macros important to health and good body composition? Yes. I usually skip that part because someone inevitably jumps in and explains how sugar is metabolized differently than fat, and then try to use that to "prove" that sugar will make you gain weight no matter what your caloric intake.
[1] https://en.wikipedia.org/wiki/Dietary_fiber#Fiber_and_calori...
More money quotes:
Insoluble fiber does not change inside the body, so the body cannot absorb it and it provides no energy. Soluble fiber is partially fermented, with the degree of fermentability varying with the type of fiber, and contributes some energy
In the US, soluble fiber must be counted as 4 kcal/g (17 kJ/g), but insoluble fiber may be (and usually is) treated as not providing energy and not mentioned on the label.
So it's technically accurate that the human body cannot digest fiber, but bacteria in the gut can break soluble fiber down allowing us to extract some small amount of energy.
Unfortunately calorie restriction that goes too far may have other negative affects... and most people don't track their diets closely enough to really tell how many calories they take in on any given day. I've gotten really good at estimating, and as long as I stay below 2500-3000/day and get at least 100g of protein, I tend to do okay as far as staying in the range I am in.
On the down side, when I try to make too much of a shift it winds up badly in one way or another (experiencing ketoacidosis is something I never want to experience again). Eating once a day a couple days a week (roughly 23.5 hrs between meals) I feel pretty good with. Eating too close to bed and I get an upset stomach. It's funny, but my own body has been a pretty big experiment in terms of trying different things to see what works, and what doesn't.
I tend to either have every negative affect to medications, or my body stops responding to them after a while. Byetta lasted about 6 months before my body stopped responding to it, Victoza about 2. Invokana is the first diabetes medication that doesn't make me incredibly ill, and actually keeps my blood sugars stable (though I've been a little more sensitive to light, and more headaches).
I truly wish I could go back a couple decades knowing what I do now. I also wish I could smack whoever started the "low fat" fad in the 70-80s, or the people behind the food pyramid.
It's not that hard, really...
* Get enough protein
* don't eat too much
* avoid too many refined foods/ingredients
* Have some raw fruits and veggies
* Avoid too many sweet fruits and candy
I don't know what the solution is, I do no that limiting personal freedom and choice isn't a good answer. Improving education and reducing religious-like or commercial interests as such would be a good start though.
Oh, sure, it's difficult to say with certainty that 100 calories on the label will be exactly 100 calories for every person ever - but there's really not a gigantic amount of variance. Certainly it's a good enough guideline for use.
It's a matter of thermodynamics more than anything else. You can't get energy from nothing. Quantifying the exact amount of energy you'll get from a food is difficult to do precisely, but the guidelines we have are good enough for use for the vast majority of people. You can be pedantic about it, but that won't change the fact that it is that simple to lose weight, as proven time and again.
And you are suggesting it's simple with no actual data to back it up. Can you cite a single study that shows that nutrition label calories were anywhere close to actual calories burned by a person. Or any mechanism people have to find calories:
Here's one that says the opposite: http://www.livescience.com/26799-calorie-counts-inaccurate.h...
For example, for most people, they discovered almonds have 20% less calories than "estimated".
http://ajcn.nutrition.org/content/96/2/296.abstract
That's a huge variance.
"but there's really not a gigantic amount of variance." Citation needed :)
"Quantifying the exact amount of energy you'll get from a food is difficult to do precisely, but the guidelines we have are good enough for use for the vast majority of people."
What do you think vast majority is? Given the variance in everything else, we are probably talking 20-30% of the population.
"You can be pedantic about it, but that won't change the fact that it is that simple to lose weight, as proven time and again."
I'm not being pedantic about the mechanism. I'm being reasonable about the fact that the method most people have to figure out whether what they have is going to be successful is useless (IE if they can't determine how many calories they eat/burn, they can't possibly change the numbers :P)
Some researchers say that, on the whole, the inaccuracies in calorie estimates don't make a big difference. "For most uses, I think they're good enough," said Malden Nesheim, professor of nutrition emeritus at Cornell University, in Ithaca, N.Y., and co-author of the book "Why Calories Count" (University of California Press, 2012).
People tend to eat a variety of foods, not just almonds or starches. So overestimating or underestimating the calories in one particular food will likely not have a huge impact on a person's daily calorie intake, Nesheim said.
And generally, the omissions in the Atwater system tend to result in overestimates, meaning they likely wouldn't interfere with weight loss.
"It would only be a problem for people who want to gain weight," said Mary Ellen Camire, a professor at the University of Maine's Department of Food Science & Human Nutrition in Orono.
The problem isn't with nutritional labels of varying accuracy, but with people under-estimating the calories per portion (without reading the label) and who serve enormous portions.