It is not true that those who eat little won't gain weight. It all depends on how fast your body can get rid of it. If you poop three times a day, like all the men I know, there's no time to gain, weight.
If everything you eat taste 👎 you stop eating. It's what children do but we force them to eat with the result many can no longer stop if they had enough. Stress eating increases too but chemicals and medication are good for gaining weight as well. 🙃