Short version: How does your body decide whether to draw energy from fat or from lean mass when in a caloric deficit from dieting?
Long version: I understand that if someone diets too severely, the body apparently interprets this as a period of 'starvation' and attempts to horde fat and use lean mass as its energy source. However, I'm very curious as to how the body determines what qualifies as too severe a diet.
It would seem to me that the body really has no awareness of a specific calorie threshold. I'd think it can't tell that it was in a 700 calorie deficit today as opposed to 500 yesterday; it only knows when the food energy runs out and it has to start munching on internal stores to make up the difference. It also knows when it's hungry.
With that in mind, is the 'starvation' effect truly due to just eating too few calories or eating so little food mass that the body really is starving? I've seen what some people attempt to get by on while dieting, and it doesn't surprise me that the body freaks out over how little sustanence is coming in. But how much of that is simply due to an exceptionally low volume of food?
I've got no idea about this, but it seems to me that as long as the body has a regular supply of food, keeping the digestive system occupied, it has no feeling that it is being 'starved'. It would seem to me that's why plans like the Velocity Diet are effective - calorie intake can be severely diminished, but you're chugging those shakes all day long and your body never gets a real sense of deprivation.
Assuming this is so, does that mean the 'starvation' effect is one more of satiation than actual calorie intake? To head off the obvious criticism, I'm not advocating dieters cut down to a thousand calories a day and gorge themselves on iceberg lettuce to 'successfully' crash diet; I understand the importance of a healthy diet with adequate nutrition. I'm simply curious as to how the body decides when to switch from burning fat to mucnhing on muscle. Long post, thanks for reading