According to WebMD, burning off 500 more calories than are consumed per day for a week should result in about 1 pound of weight loss a week. Therefore, 3,571 crunches each day over the course of a week should result in 1 pound of weight loss.
William McCoy for the Houston Chronicle reports that HealthStatus says that crunches burn relatively few calories, only 84 per 15 minutes of high-intensity crunching. SparkPeople reports that the American College of Sports Medicine lists 40 crunches per minute as a high-intensity level of crunching. Therefore, each crunch burns around 0.14 calories. Ninety minutes of high-intensity crunches per day is necessary to produce 1 pound of weight loss per week. This is equal to about 3,571 crunches per day for a week.
Crunches are good exercises for toning muscle and building core strength. Developed core muscles often make the torso look slimmer without weight loss, and a strong core makes it easier to perform many of the aerobic workouts necessary to burn fat and shed pounds. For many people, the ideal exercise program blends aerobic and strength exercises.