What could cause heart palpitations while fasting?

Here's the thing a lot of these water soluble nutrients don't get stored in the body very long. So when you fast you're not eating and you might be already deficient like a lot of people are. And all of a sudden you become very deficient especially with potassium and even the water soluble vitamin B1 both of those if they're deficient will cause an elevation in the pulse rate. What you want to do is take, especially when fasting, electrolytes with potassium and then the B vitamins. That should solve that problem pretty nicely.