Underweight, still cleanse?

I am planning on starting The Master Cleanser in January to mark my change in diet and lifestyle. The only thing that I'm concerned with is my weight. I'm very thin - approximately 6'3" 150lbs. Should I still fast for 10 days? Is is safe for me? If so, what can I expect after completing the fast as far as my metabolism? Is there anything else I should know about other than what's in the book? Tweet