How can I prevent cramping and nail splitting during prolonged fasts?

Biotin would help. That usually comes from the gut. It's in the category of B vitamins, but also silicon also is good for nail cracking. But I would look at both of those being a problem, especially if you're doing fasting, you're probably going to add some supplement to that.

Dr. Berg Nutritionals staff, including Dr. Berg Advisors, do not encourage prolonged fasting. We are not healthcare professionals equipped with the tests and facilities to perform the necessary monitoring during a prolonged fast, nor do we have an individual's medical health records. Dr. Berg Advisors provide this document based on Dr. Berg's education for informational purposes only to those already on a prolonged fast or independently choosing to do one.

Always consult with your healthcare provider before starting a prolonged fast.  If you're considering prolonged fasting, discussing the benefits and risks with your healthcare provider is essential.

Dr. Berg's Guidelines for Prolonged Fasting.docx.

•  https://www.youtube.com/watch?v=2VXvVuMk9ks 

• https://rumble.com/v1m7qps-7-critical-things-to-know-about-fasting-prolonged-dr.-berg.html