I a 32 yo female who was always the skinniest kid in school. I have a petite frame and was naturally tiny growing up. I was also a weakling when it came to physical activity. Suddenly I went from being around 100 lbs at 5'4" to 150 lbs in just a couple of years. Turns out I was hypothyroid. I started thyroid medication, walking, and reduced refined sugars/carbs and lost 30 lbs. I've maintained my weight loss for the past 5 years by watching my diet and running. I miss the days of being able to eat whatever, whenever, but there's no sense in wishing for the past. In a way it was the best thing that could have happened because I never would have started exercising otherwise.