I need.....

That post that explains how a lifetime of dieting will wreck our metabolisms please.

I don't know which post you are referring to, but...

The short version(s):
Short term calorie restriction leads to a loss of lean body mass before the body switches to burning fat for fuel, so lots of short term dieting leads to a loss of muscle, which essentially lowers the metabolic rate of your body since muscle tissue burns more calories per ounce than fat.

The body is adaptive and will adapt to calore restriction by slowing down all of the processes of the body so that you are made more efficient and can run your body on fewer calories, but accomplish the same thing.

So by adapting the body becomes more efficient on fewer calories thereby taking longer to burn through the muscle phase before it gets to burning off the fat right ?

I'd never heard that one before.  Spending prolonged time burning muscle before switching to fat burn mode, is that what you're asking?  Again, haven't heard about that.  But, if you spend more time going on and off diets, you enter that short period of time when you burn muscle tissue more and more often.  And the more times you do it, only to rebound and eat normally, the more and more times you destroy muscle to get by, without actually burning as much fat.  (you switch to fat burn after a few days of calorie deficit--brain starts relying more on ketones)  So you go off the diet, have destroyed lean tissue, only to get off the diet and have less muscle mass (meaning slower metabolism) which causes weight re-gain when you start eating normally again.

Body being more efficient would be like...two companies doing the same thing but one of them has figured out how to do it 100 million dollars cheaper. 

I believe it has even been found that obese people don't even expend as many calories as a lean person in non-exercise activity...like little ticks, jittering, pacing, etc.  just little movements each day that aren't actually exercise, but still burn calories.  If your body wants to survive on fewer calories per day, it may not drive your body to make those little movements to burn excess calories.  Stuff like that.  Little things adding up.  Spending less calories to move, breathe, keep warm, etc.  Keeping you running without spending as much money, so to speak.

Thank you for that explanation that helps. Is there any medical terminology for this function ?