In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
If your physician advises you against fasting because of anemia, then you should skip the fast.
In responding to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
As far as I can learn from postings from physicians, anemia may not pose a challenge to fasting, once correctly managed and controlled. It may, however, vary from person to person; so, you should consult your physician.
Let him recommend what is best for you. If your physician advises you against fasting, then you should skip the fast. It would be best if you fed the poor by way of compensation. If, later on, your condition improves and it is safe for you to fast, then you should make it up.
Almighty Allah knows best.