It's not about just randomly breaking the cells, it's a normal process called autophagy where damaged cells are being recycled to be replaced by new ones. This happens all the time, but it seems that fasting can increase it significantly. The leukocyte count only temporarily falls, and then gets back to normal. This is extremely beneficial to chemo therapy patients because chemo damages cells, suppressing the immune system as a side-effect and also makes people feel very sick. This can reduce these effects.