What happens to eat less than your basal metabolic rate?

[UserReqDel20200217]

What would happen?

[Gordo]

You lose weight.  If you have fat and/or muscle to spare, you will slowly lose it, but it is possible for a very fat person to go a whole year without eating anything.  If you run out of fat and muscle to catabolize, you will eventually die, but typically what happens is some organs start to shut down and the anorexic end up in a hospital where they are force fed through a tube, thus preventing death.  Hope no one here goes down that road...

 

[drewab]

I'm wondering if there is more to the question than you are leading on to ask. Are you wondering if your BMR changes with long-term calorie reduction?

[Sibiriak]

Yes, its an interesting issue,  what effect CR, short and long term, has on BMR (RMR),  as well as on homeostatic body weight regulators such as leptin, , ghrelin , insulin etc.,  in relation to body weight set point.

[mccoy]

A direct answer might be that, according to the setpoint theory, the BMR  will reset to a lower level.  So, after the readjustment, the caloric intake might not abe any longer lower than the BMR, provided we cut other energy expenditure such as muscular output and thermal output and so on (which by the way tend to be decreased byt he hypothalamic feedback mechanism itself).

 

So probably the question should be riformulated such as:

Q: What happens to eat much less than your basal metabolic rate?

A: As Gordo says, you starve and eventually die

Q: What happens to eat a little less than your basal metabolic rate?

A: you may survive, in a state of reduced thermogenesis and activity, after the bodyweight setpoint has shifted down to a lower BMR plus a small delta for basic movements, thermal and other energy loss.

 

 

[Ron Put]

Your BMR generally drops as you age. Exercise counteracts such drop significantly.

Sensible CR practice is key of course. Anorexia nervosa is rather rare, especially in males and while often thrown around in the media, obesity is far more common and kills many, many, many more people in the developed world than malnutrition.

Here is a study on monkeys which may provide some answers to how CR relates to BMR:

"The result shows that caloric restriction reduced adjusted daily energy expenditure in multiple studies on the order of 171 to 293 kJ/d."

https://academic.oup.com/jcem/article/88/1/14/2845989