From time to time, generally when there’s a public case of a hunger strike, people ask me how long a person can survive without food.

The hunger strike generating attention at the moment is that of Russian opposition leader Alexei Navalny.

Navalny, who was arrested in January after returning to Russia, began refusing food on 31 March in protest at not being able to access medical care in prison. This means he’s been fasting now for more than three weeks.

Based on the science of long-term fasting, Navalny could theoretically continue his hunger strike for another number of weeks.