[jacques_chester]

> I don't fully understand this compulsion to explain anything successful in the weight-loss field, ultimatlely, in terms of calorie restriction.

Because any other hypothesis has to explain why it violates the conservation of energy and matter. (Also: such studies are harder than they look to arrange. Completely controlling someone's caloric intake and output is difficult to achieve).

What tends to happen in discussions such as these is that they devolve into a shouting match about the boundaries of causality. In a basic physical sense, caloric balance is the only thing that matters. It is the causal element. Cut calories enough, you will lose weight. Raise them enough, you will gain. The relationship won't be linear, immediate, proportional or unary. But it will be causal.

But that's oversimplifying! comes the cry. And it is. The internal mechanisms of the body mediate and modulate weight control in interesting ways. The ever-plunging $:calorie ratio has its input. And so on and so forth, ad infinitum.

Proponents of IF talk about various interesting biological pathways that turn on and off, hormone levels that change and so on. But the direct cause of weight loss in IF is that you simply do not eat as much. You can't, you've removed entire culturally-important, structured opportunities to eat. Gone, just like that.

[anamax]

> > I don't fully understand this compulsion to explain anything successful in the weight-loss field, ultimatlely, in terms of calorie restriction.

> Because any other hypothesis has to explain why it violates the conservation of energy and matter.

Umm, no. None of the weight loss diets violate the conservation of energy and matter. (The "I lived on just water for 10 years" diets do.)

Feces contains calories. Therefore conservation of energy isn't the only limiting factor - conversion and usage matter too.

There's no "conservation" argument that says that conversion effectiveness is a constant. Heck, there's no argument that says that calories/pound is a constant.

> But the direct cause of weight loss in IF is that you simply do not eat as much.

Nope. You lose weight when your body "releases" more mass than you're taking in.

[backprojection]

> Because any other hypothesis has to explain why it violates the conservation of energy and matter.

This comment is so infuriating. I may not be a genius, but I did manage to eek out a degree in physics. I think I, and anyone here on HN should be given the benefit of the doubt that they can figurer out if energy conservation is being violated.

Simply from a principle of assuming that the person suggesting the hypothesis is not an _idiot_, you could infer that any of these alternative hypotheses do _not _ violate energy conservation.

[jacques_chester]

I have found myself arguing with people who took the view that the conservation of energy and matter does not apply to sufficiently complex biological systems.

I am quite serious.

[randallsquared]

The relationship won't be linear, immediate, proportional or unary. But it will be causal.

So... you agree with the comment you're replying to, then?

No one disputes that a body cannot burn more energy than it has taken in. However, other factors can swamp a "mere" 25% percent reduction in caloric intake. IF has been the most effective weight loss strategy for me, but it doesn't work forever unless you keep reducing the amount you're eating. Eating only every other day worked great for two months or so, but eventually the loss tapered off (this was 2010), and something else must be done. The body doesn't need nearly as much energy as we typically give it, apparently, and varying the amount discarded can affect weight gain or loss greatly.

[jacques_chester]

One thing you probably overlooked: fat cells add to BMR.

[randallsquared]

While I didn't overlook it entirely, it's true that it is quite difficult to know how to account for it without , since resting metabolism varies widely ( http://en.wikipedia.org/wiki/Basal_metabolic_rate#Causes_of_... suggests more than 25% variation after accounting for a number of potential factors). My own anecdotes suggest that once the (my) body adapts to higher caloric intake, it discards much more of it than when times are leaner.

[jacques_chester]

25% is for extreme outliers.

http://examine.com/faq/does-metabolism-vary-between-two-peop...

BMR varies mostly on body size. Taller, heavier people have a higher BMR because there's more of them to keep alive.

[beagle3]

> Cut calories enough, you will lose weight. Raise them enough, you will gain.

That's true in the useless tautological sense.

I've read a case study a few years ago about someone who has to eat something like 10,000 calories a day, because after some serious illness, their body only takes in 20% or so.

Paper is also carbohydrates - albeit not ones that our gut can process. Any statement about "caloric intake" is so hard to measure to make statements about "caloric balance" vague. They are useful as a "small signal"[1] approximation around common steady states (which are often 1000-3000/kcal a day, although that's not a good characterization).

However, when you go away to this state, this approximation breaks down and stops working. A model that would have predictive power in the "large signal" setting would have to take your entire biomass (10 times as many bacterial cells, although only 10% of body weight; 30% or so of solid excretions; facilitators of many processes), and nonlinear effects of insulin, ketosis, and others.

[1] http://en.wikipedia.org/wiki/Small-signal_model