If you want to gain weight it helps to incorporate high-calorie foods that don’t stimulate the over-full feeling, so something high in sugar like soda or ice cream. Obviously eating enough of that can cause metabolic disorders, but over time eating these kinds of foods will be fattening, though it can take a bit of time as your basal metabolism will increase and burn up the extra calories at first. Just be moderate I guess, obviously these are unhealthy tips, lol.

I have the opposite problem though, I struggle with losing weight and not over-eating (even when I’m eating really healthy foods). Fasting has helped me lose weight, personally.