Not necessary lying. But I have read countless stories, where the TLDR; would be "I thought I was eating very little and very healthy but then I bought a kitchen scale and started weighing and logging everything and OMG was I wrong".

I was also sceptical about counting calories and never needed to do that and was at healthy weight. But recently started for some fitness reasons, and here's a personal anecdote for fun:

Greek salad is a very healthy meal, where olive oil, a very healthy oil, is used as a dressing. So I always just put "some" in it. With a scale, turned out that was 40g. That served 2 people, but still: almost 200 cal from just dressing from just one meal. Another thing I noticed was that olives and feta cheese were under 20% of the salad volume, but over 80% calories. So just by varying the amount of these I could bring the serving calorie content anywhere from ~100 cal (substituting olive oil with balsamic vinegar) to ~500 cal.

So I can see how people may honestly say "oh, but I eat nothing but salads and still can't lose".

why is it impossible to vary with one individual over time, or change drastically in a short period of time?

Because there is little to no evidence for that, and I'm talking about metabolic ward quality evidence.

Sure, if you're in calorie deficit, your metabolism will slow somewhat, but not drastically and not in a short period of time. Sure, some medication plays tricks with hormones that regulate hunger, but not so much with metabolism directly. I don't know about conditions where metabolism will drastically slow down in a short period of time. Even under water fasting it takes at least 72 hours of 0 calorie intake to notice a measurable change.

Do you happen to know (I don't) if "caloric uptake" specifically has been studied closely? Specifically:

* When you consume <x> calories, how many are extracted by the body and how many are excreted? * Can this vary by food type? * Can this vary across persons, and across time for the same person?

From personal experience I have witnessed what seems to be impossible, and my diet was so simplistic (sausage, bacon, spinach, multi-vitamins) that I couldn't have been making a mistake, yet I hit a plateau. The only logical explanation I can think of is a massive short term change in caloric extraction.

No - I also don't know. I haven't seen it mentioned, but I also haven't seen reports about the amount of calories absorbed by the body change for no reason at all. So I'm not completely discarding the possibility, but I would like to see some studies and at least an attempt of explaining what might cause it.

The only logical explanation I can think of is a massive short term change in caloric extraction.

I can come up with some more: 1. The water retention, or the so-called "woosh effect"

http://www.bodyrecomposition.com/fat-loss/of-whooshes-and-sq...

What’s going on? Back during my college days, one of my professors threw out the idea that after fat cells had been emptied of stored triglyceride, they would temporarily refill with water (glycerol attracts water, which might be part of the mechanism). So there would be no immediate change in size, body weight or appearance. Then, after some time frame, the water would get dropped, the fat cells would shrink. A weird way of looking at it might be that the fat loss suddenly becomes ‘apparent’.

Now this article is not rich with links to science, so take it with a grain of salt.

2. As you lose weight, your caloric requirements naturally go down. So to remain in deficit, you have, unfortunately, revise your targets down from time to time, otherwise you reach balance and stop losing.

3. Somewhat related is the decrease in NEAT - Non Exercise Activity Thermogenesis. In short, you tend to be less active when you are in caloric deficit, and may not consciously notice it. Sorry for the same source again, it happens that this guy writes a lot on the subject.

http://www.bodyrecomposition.com/fat-loss/the-energy-balance...

For example, say you put yourself through 500 calories of hard activity but, due to fatigue, you sit on the couch more later that night, burning 300 calories less than you expended before training. The supposed 500 calorie deficit you’re creating is really only 200 calories because your SPA/NEAT has adjusted itself. You might expect one pound per week fat loss but the deficit is actually less than half of that

The whole article is a very good summary on the mathematics of weight/fat loss.

Similarly, as I said in a message above, there is a lower limit for how much energy your body must burn in order to maintain body temperature. You will find if you look at the rate at which corpses lose heat to ambient temperature that it is very, very close to what is listed on those base metabolic rate charts. Again, I have to stress this: you can not burn less than that without decreasing your temperature and dying. It is a physical impossibility.

There are obviously variations, of course, but they must (by physical necessity) be on the up side. So you can easily eat 3000 calories and not gain any fat, even though you don't exercise, if you have a thyroid problem, or if you have a digestive problem that causes food to shoot through you before you can process it.

On the other hand, you can not (due to the laws of physics) eat less than the number of calories required to maintain body temperature and not lose weight. This is conservation of energy. And as I said, the minimum amount of energy required to maintain your temperature is very close to those base metabolic rate charts.

Sure you can be off by 100 calories a day. You can't be off by 1000. It just isn't possible. So if you are in deficit for several hundred calories a day and you aren't losing weight it is necessarily because you have measured your exercise or diet incorrectly. As I stated several times, this usually occurs because companies outright lie about how many calories you can burn through exercise (and are often off by 1 or 2 binary orders of magnitude). It is also because people completely overlook high calorie foods, even if they are otherwise very careful.

Do you happen to know a typical range for this? For caloric maintenance level, there is:

* Body temperature maintenance * Operating bodily functions (pumping blood, breathing, etc) * Basic "non-exercise" movements

For all of these, calories consumed (eaten) must take into consideration:

* caloric extraction (basically, net of calories remaining in excrement) * caloric consumption efficiency (of those retained, how efficiently are they converted into heat & kinetic energy)

There are actually two sets of numbers for the first three points: actual literal calories required, and then the set that takes into account the last two points. How different are these numbers? I wonder, assuming this "weight plateau" while still in what is thought to be caloric deficit is actually real, could the general understanding of the last two points not be correct in all situations?

As discussed, it seems some people extract more calories from the same food (for whatever reason), although how true is that? The other alternative is that they have similar bodily behavior as someone with a thyroid problem (calories are uptaken (I think?) but not stored as fat - not sure how this works then, are they excreted?), but if on a strict diet, the body could change causing a plateau.

I don't think I'm doing a very good job of explaining myself.