As a thyroid failure (Hashimoto's) sufferer, weight has been a constant problem. The instant my thyroid failed, my weight went from an athletic 175 pounds, bicycle racer, to 239 in 6 months. No change in diet or exercise. In fact, I even tried to make my training bicycle rides longer.
I was determined to get back to 180 pounds or less. What it took was nothing short of staggering. I was down to a salad with 4 ounces of fish for lunch and nothing else. No dressing, no cheese or bread. Of course, my energy levels plummeted but I reached my goal. I was unable to exercise unless I fed myself, so I added in some workout fuel and weight came right back. The best new normal was 205 pounds and daily gym workouts.
However, when I travel to remote countries, I lose some weight. It seems the natural local foods don't contain the compounds our foods do. I can be less careful in rural Italy or Africa and not gain weight.