The National Health Service publishes some excellent advice on how to stay healthy during Ramadan.
The main page is "Healthy Ramadan" at this link. From that page you will can go on to many others with medical advice on how to fast safely during Ramadan.
We also recommend looking at the 30 page PDF document "Ramadan Health Guide" whose creation was supported by the NHS. Towards the end it also has some key points in foreign languages. It is at this link.