> If you employ a caloric restriction diet, you must do something to keep your metabolism from down-regulating

No you don't. You will always burn calories by simply existing. You can get no exercise and still lose weight simply by cutting calories. Cutting 100 calories from your daily diet may be matched one-to-one with metabolism decreases, but I guarantee that if you cut 1,000 calories from your daily diet you will lose weight.

In the degenerate case where you restrict your diet to zero calories over an extended period of time, your metabolism will permanently down-regulate to burn zero calories.

I think most people agree that should be avoided.

That is not true. What do you think the purpose of fat is? As long as you have fat supplies, your body will use those fat supplies. Example: http://www.abc.net.au/science/articles/2012/07/24/3549931.ht...

It was a tongue-in-cheek reference to death from complete starvation. It is true in the sense that the basal metabolic rate of a dead body is zero kilocalories per hour.

Yeah, because consuming fewer calories than you burn at your basal metabolic rate is totally sustainable.

You don't have to do it forever, you just need to do it until you're happy with your weight. I've personally used this method of weight loss because I find it very difficult to exercise effectively when I'm running on a caloric deficit. I consumed 1,000 - 1,500 calories a day for ~2 months and lost ~20 pounds, then began living life normally again. I found it more sustainable than grinding out weight loss over a much longer period of time by exercising.

If your only goal is losing weight, might as well chop off your legs, lose 50 pounds and be done with it.

Hint: nobody's goal is just weight loss.

Lowering your BMI from 31 to 24 by cutting fat makes you healthier and increases your expected lifespan (regardless of whether or not you exercise), chopping off your legs does not.

Yes, BY CUTTING FAT.

See, your goal is not just to lose weight. Your goal is to lose fat. Your body will burn a hell of a lot of muscle if you just sit still and not eat.

And becuase you're burning more muscle than fat, you're even going to lose more weight. Hooray!

For added bonus, you can lay in bed all day so that you lose bone density as well. Even more weight loss even faster! So much better BMI. Much healthy and awesome.

Point is, nobody's goal is JUST to lose weight.

That wasn’t true for me personally. I personally lost weight almost with mechanical precision. About a 7500 calorie deficit resulted indeed in 1 lost kg. That’s with about half the deficit coming from exercise and the other half coming from cutting calories and is using all the bog-standard formulas for roughly estimating my base metabolism. I was astonished by the mechanical precision of those number, really astonished. I didn’t expect that at all.

However, this has many moving parts and cheating (mostly by consuming more calories) is ridiculously easy. My guess would be that that’s the effect many people see when they don’t succeed. All of this is really hard and I was lucky to be in an extremely privileged position where I could devote lots of my attention to this task. Not many people are so lucky. Motivation obviously plays a crucial role and I absolutely do believe that it is central to successfully losing weight. The mechanics are simple and do indeed work like clockwork. But that doesn’t mean you can make them work like clockwork for yourself …

So, yeah, the body may be astonishingly mechanical when you execute everything perfectly, but motivation is the crucial second parts that allows you to execute everything correctly. And it may well be that to keep motivated it helps to be active or to eat certain thing. (I, for example, know that eating pasta with tomato sauce – formerly my absolute favourite food – will keep me hungry for longer. Meanwhile the same amount of calories from some salad with a vinaigrette and grilled chicken breast will keep me feeling full for longer.)