It is generally accepted that you have to burn 3500 calories from fat in order to lose 1 pound of fat.1000 sit up walking or jogging a day is recommended. So if 50 sit ups is about 10 calories, then you would have to do 17,500 sit ups in order to burn 3500 calories. If you did 1000 sit up every day for 2 weeks you’d only be at 14,000 sit ups. Hopefully, you can see that using sit ups to burn fat might not be the most efficient workout strategy. Aerobic exercise, sports activities, or total body weight training are better choices for burning body fat.