<span>The cycle of losing weight and gaining weight time after time is called yo-yo dieting, so the correct answer is C. Yo-yo dieting is often a result of fad diets, where the diet used to lose weight is unsustainable for a long period of time. This unsustainability could be due to a number of factors, such as the type of foods consumed, unrealistic workouts, or using diet gimmicks. Diet gimmicks, such as weight loss pills often produce quick weight loss, but these results aren't always sustainable without the pills. Sustainable weight loss is created through proper diet and physical exercise. This type of lifestyle change is necessary to avoid yo-yo dieting.</span>
