Calories In < Calories Out ... But How Much Less?

vronster

I've been lurking on this forum for awhile, long enough to witness the craziness that accompanies any post about the ideal calorie intake and output for weight loss. Now, I don't want to add fuel to that fire, and I understand that every body is different - what works for one person doesn't necessarily work for another. Still, I'm wondering what the more scientific-minded people on here have to say about the various ways of estimating your calorie needs and expenditures to lose weight, because the anecdotal evidence is kind of ... ambiguous.

Scientifically speaking, when does a healthy caloric deficit transition into metabolic damage? Is there some kind of ratio for calculating or charting that? And once your body grows accustomed to an inadequate caloric intake, does your BMR drop, thereby reducing your energy output? Is that what metabolic damage actually is? And if the amount of calories needed to lose weight and, presumably, maintain at a lower weight are so much higher than the oft-quoted 1,200/day, why are MFP and other diet plans so off-base? Can a metabolism slowed by undereating ever return to its previous rate?

We all know that weight loss requires consuming fewer calories than your body uses. Therefore, it seems reasonable to assume there's a spectrum with "eating too much" at one end, "not eating enough" at the other end, and "maintaining" in the middle. So I'm confused about how it is that one can maintain the same weight with a high OR a low caloric intake. I guess you could say I'm doing some trial and error with my own diet and the results have been inconclusive. I'd very much appreciate any science-based info or suggested reading you wonderful people can provide!

Haha, yes, I realize I'm overusing the word "science" in this post, I just want to be clear that I'm not looking for advice, just explanations.