Can I use exercise on the fast day to earn more calories?

Technically, you can, but we don’t recommend it. People tend to grossly overestimate the number of calories they burn while exercising. This happens because most exercise machines overestimate calories burned by 50-100%. For instance, a typical elliptical machine will tell you that you’ve burned 300-400 calories in 30 minutes, when in actuality, most people will only burn 100-200 calories. Because of this overestimation, people often leave the gym thinking they can eat a 400-calorie snack. However, if they do this (when they’ve only truly burned 150 calories), they will be eating 250 calories more for the day, completely negating the effect of the exercise!