So I've been thinking, which can sometimes be a dangerous thing..
An argument against fasting sometimes seems to be that it results in muscle loss. So I'm curious how selective our bodies are about where they'd scavenge protein from in a starvation situation. I'm assuming from an evolutionary perspective, it'd be sensible if that were selective in some way, but curious if that happens, or is possible.
Great question.
Imagine you are a car - a car that can make alterations to its size, engine size and the amount of luggage it carries. The objective of the car is to get to the next stage. To do this, it need fuel.
Suddenly, fuel becomes limited. (You are fasting.) What do you do?
You could loose the luggage - all that excess weight which makes you feel secure (comfort eating??? = bare with me) and none of that luggage contributes to fuel efficiency. Loosing the luggage from the boot or the roof rack would improve efficiency and make your fuel last longer. But who wants to throw out their stuff.
You could reduce the size of your car, but it's not easy loosing your frame. Who can reduce their skeleton grom 6ft 2 to 5 ft 8???
You could reduce the size of your engine. You would probably have to loose some luggage at the same time. Smaller engines go further but would be under a huge amount of strain if the size of the car or the amount of luggage is not reduced. Try sticking a 1.1 litre engine into a fully laden people carrier and see what happens.
So now let's look at the human body.
Reducing engine size is quite easy - i.e. reducing muscle mass. It only take 1 week out of the gym and I notice that my clothes feel baggier on me, but make the engine too small without reducing the luggage and you will end up with problems.
Smaller muscles use less energy - you tend towards sluggish. Carrying all the excess luggage (fat0 will only make the problems worse. Follow this to its natural conclusion and you could end up with a body composition where fat is higher than muscle mass - in other words your car is overloaded with luggage and the engine is too small. you will never reach your destination - or if you do, you will not enjoy the ride and your health/well being will suffer.
Which muscles waste first - that depends - we have to assume there is some level of exercise, using legs, arms etc. First thing to go with me - even in just one week off - the shoulders. There are no natural movements that take the place of heavy shrugs or shoulder presses and unpacking the groceries doe not even come close.
The best way to do the type of fasting some diabetics follow, is to combine it with exercise - tell your body you need the engine and just jetison the luggage.
PS - big muscles use more glucose and help with blood sugar regulation.
I train for strongman 5-6 days a week. I don't fast. I take 1-2 weeks off every 6 weeks - to recover and stop from going stale. My plan for staying alive is very dependent on not getting bored with exercise. I'm 53 and still get excited about going to the gym - every time. (T2 Oct 15 - met, exercise and diet, not fasting - complete opposite in fact!)
Sean