Artificial feeding has been recognized as a form of torture for 30-40 years, therefore it is prohibited. But in our conditions it is extremely difficult to control compliance with the rule of law. Of course, people like Savchenko, Belykh, Khodorkovsky are always in sight, and if they tried to feed them, it would emerge in a few days and cause a huge scandal. Another thing with an ordinary convict, the administration can do whatever.
Not only they can, but they have actively done and are doing this, and in different countries and at different times. Read the memoirs of Bukovsky or watch the film "Suffragette" - this is the first thing that comes to mind