After gaining the freshman 40 during college, my weight-loss journey was a long one because I made so many mistakes. Many of them were diet-related, including eating too much in general (holy 800-calorie smoothie!), eating too many carbs and not enough protein, and overdoing it on high-calorie “health” foods like nuts. But, I also made many fitness-related mistakes that actually led to weight gain! If you’re looking to get leaner with exercise, experts agree — avoid these fitness mistakes.