Fasting during Lent season?

I'm 19 years old. I'm 5'1 and I weigh about 120 pounds. Is fasting a safe practice to do at this weight? How can I prepare and end the fast? Is water or juice fast safe? How can I get nutrition? Can I be able to conceive children in the future? I'm in the Christian religion. If I loose too much weight, I will stop the fast.