I'm fasting today

For instance, there is the system that excises oxygen from air in the lungs and integrates into the blood stream for distribution to vital organs. If you're in any way unsure about this system, allow me to be the first to ensure you that this is not an internal system that should take a break.

Bad example. The circulatory system is well involved in the digestive process. When you eat your heart rate goes up to get more blood to the stomach area. To test this, go eat a big meal, then get straight on your bike and ride 10 miles at race effort and see how sluggish you feel.

Fasting will rest the digestive system, so place a reduced demand on the heart. There may be (probably are) other effects on the body that negate this during the fast though.

What I don't see is anyone asking how long the OP was fasting for? The book says 18 hrs to start with and to start after dinner one eve (so skip breakfast and have a late lunch basically) - as a one off or occasional activity it probably isn't worth the reaction it's brought from the forum massive.

I reckon that many of you will have done the fast described above unintentionally in the past, and are none the worse for it.

No, no, you've got it all wrong. These are the books:

I'm sure that's meant to be funny, is it not?