question on RMR/BMR confusion

so I understand that if we don't eat enough calories,  we run the risk of lowering our metabolism.

many here said that a 5'2 100lbs girl needs 1200cals just to maintain the healthy function of their organs.. ( i don't know whether it's really true because no source of this information was stated)

anyway, so no matter what, our BMR can't be lowered in a sense, because that's what we'll definitely burn no matter what as long as we still have our organs intact in our body, right?

so if we lower our metabolism, it means we lower the RMR? or issit the BMR?

I'm sure there are examples where the BMR can drop to less than 1200 but they would be 'in extremis' and not the norm.  

Metabolism speeds and slows all the time.  Skip a meal and it slows a little... do some exercise and it speeds up a little.   Go to sleep for several hours and it slows..... eat breakfast and it speeds up.   Someone who should maintain their weight on 2000 cals a day but who eats 1800 cals a day over a long period of time will slow their metabolism eventually.  Someone who crash diets on sub 1000 cals will slow their metabolism pretty quickly.

Try not to look at your weight management in terms of how little food you can get away with but in terms of how much you need to live healthily and lose weight safely. 

up?

BMR is an approximation.  It is impossible to be completely accurate with the BMR or RMR.

The BMR is a generalisation of the approximate amount of calories needed for the organs to function normally. In general, after prolonged periods of starvation (ie less than the BMR), the body can adjust to function on what it is given, but it will not be working to full capacity, thus resulting in lethargy etc.

Even after this period of starvation, if the dieter was to begin eating more than the BMR again, the body would continue to only allow the organs the amount of calories which they had been given during the starvation period - after all, the body can function on this, and it allows the body to store energy as fat in case more prolonged starvation is approaching.

And a 5'2 girl weighing 100lbs would have a BMR of around 1286.  If their BMR fell significantly below this, then they would either be suffering from problems with the thyroid, or their organs would be at risk of failure, as they would not be getting the necessary amount of energy to function normally. If this was the case, the participant should be eating significantly over the 1200 calorie mark for a prolonged period of time, in order to allow the body to gain some weight and attempt to fix the metabolism, because in most cases it CAN be fixed - it just takes a helluva lot of time and effort. 

Your body will slow up or speed up the BMR to keep you alive.  It will also take away from body parts to sustain life.  So if you are eating too little and it need to keep your heart pumping, it might not feed your skin, or hair or nails for example,  everything it needs to look and feel great...Get the idea? 

What we all need to do is get the body used to taking nutrition from good food sources, fruits, veggies, protein (eggs, milk, yogurt and yes, even cheese- remember moderation in all things!) while providing energy for the maintinance of our bodies and add exercise so that it thinks that this is the correct BMR to provide energy for!