This is Dr Purnendu Nath, 46, a British-born Hindu.
And for the last 23 years, he's fasted for Ramzan.
And what's more impressive is that even during his fasts, Nath trains, runs marathons, goes to the gym, exercises daily, and frequently goes on treks.
"During this month, during the day when the fast is on, everything else is meant to remain the same and without a fuss," he said. "I exercise daily, so one more thing that does not change during Ramzan is this aspect of daily living. I have been trekking numerous times – the others did not even know I was fasting."