The Beachbody 21 Day Fix is a diet and exercise program that promises quick weight loss of up to 15 pounds. The diet plan emphasizes whole foods without unprocessed ingredients, which are often rich in nutrients while also being lower in calories. The plan also encourages 30 minutes of cardiovascular exercise a day, which is helpful for weight loss and heart health. This 21-day diet plan is relatively safe; however, some people may find they're not getting enough daily calories to convert to energy for exercise. Weight loss is possible on the 21 Day Fix, but since it's not meant to be a long-term diet plan, some people may regain the weight that was lost once the diet is over, should they return to their usual eating habits.