[w-j-w]

That's a bold claim. Calories as a concept can be derived from the principals of Thermodynamics, to which the human body adheres. The conception of calories does however ignore the body's natural response to calorie restriction, and is therefore incomplete.

[8note]

Calories can't explain why I can't live off of drinking gasoline, despite the bomb calorimeter showing it to be highly caloric

Calories are an simplified approximation, where your body handles things in the same way as a fire does.

Calories are bunk in that there's a random function between the thermodynamics your body adheres to, and the thermodynamics the food adheres to. One with properties like the total calories your body has access to must be less than the total in, but for a specific food, or a specific meal, the total calories could be larger than the food in the meal, if it makes other calories easier to process, or even a negative, if it makes you puke.

[kelseyfrog]

I know this is a bit hyperbolic to prove a point but it brings to the surface a point which so far goes unaddressed: the modulation and variation of metabolic efficiency.

Between the consumption of glucose and gasoline, there exists a spectrum of efficiency in the conversion of thermodynamic calories to useful bodily energy.

Take glucose for example. It's thermodynamic and metabolic calorie values are nearly equal (15.5MJ/kg or 3.7kcal/g). On the opposite end is gasoline, thermodynamically it's 46 MJ/kg but it's 0kcal/g if one were to ingest it. There simply isn't a metabolic pathway to extract energy from gasoline in human physiology.

I have no reason to doubt that the ratio of thermodynamic to metabolic efficiency varies amongst individuals, over time, and in the presence or absence of other compounds. When 9-14kcal/day supports the maintenance of 1kg of body mass in equilibrium, it's clear that, ceteris paribus[1], minute changes in metabolic efficiency can explain rather large differences in human mass.

1. Truly. Even/especially in the absence of differences in consumption.

[errantmind]

Food calories / caloric consumption, as an idea, are a gross, erroneous oversimplification of bodily processes to the point of being bunk science.

[TheSpiceIsLife]

This is correct.

Any weight loss / weight gain regime that doesn't consider, at the very least, thyroid hormones is bollox.

Steroidal sex hormones can play a role, particularly female sex hormones.

Allergies too.

[kragen]

typically the mechanism by which thyroid hormones are understood to affect weight gain is through appetite (calories in) and metabolic level (calories out) so they probably aren't really an exception to the calories-in-calories-out model

i mean as far as we know they don't enable you to digest carboxymethylcellulose or anything like that (one of the many common additives on my suspect list)

it's not totally inconceivable; some commensal enteric bacteria can digest carboxymethylcellulose, and they generate heat when they do so, and at least when it's cold outside that's heat you don't have to generate by shivering or physical activity, and we have such a poor understanding of what affects the intestinal microbiome that it's actually possible that thyroid hormone levels are important, but there's no evidence suggesting that this is the case as far as i know

but even on industrially produced diets most people probably don't eat enough carboxymethylcellulose and xanthan gum and shit like that for their digestibility to make a significant difference in their caloric intake; as i understand it the reason industrial food engineers use gums like these is that very small amounts of them can greatly increase the viscosity or gelling ability of foods, so you don't have to spend as much money as you would with more traditional thickeners like gelatinized starch

like, three grams of this carboxymethylcellulose i have here can turn 100 grams of water into a thick slime, but i would need about 30 grams of cornstarch to do this (which i would then have to cook)

(i think this is typical but your results may vary depending on the degree of functionalization of your cmc)

so if newly popular gums like this do cause obesity, it's probably through some kind of inflammatory mechanism or something, not by directly supplying calories