If you're having trouble keeping healthy weight eating normal food, it may be that you have some digestive disease/problem rather than just "fast metabolism". (Or it could be an appetite problem.)
Consider this: if you had a fast metabolism, your body would be producing more heat than a normal person; where else would the extra energy go? This means you would prefer lower-than-normal room temperature. If you're having trouble keeping weight AND you prefer higher-than-normal room temperature, it means you're not getting all the energy you should from the food you eat, in other words, your system is digesting food incompletely.
I do have a digestive disease myself, and at my worst before surgery + medication, I was drinking glasses of custard every day just to stay above 155 lbs; I'm a pretty tall guy, ideal weight that I'm seeing now is around 190 lbs. I gained 30 lbs in one month after the surgery.
Consider this: if you had a fast metabolism, your body would be producing more heat than a normal person; where else would the extra energy go? This means you would prefer lower-than-normal room temperature. If you're having trouble keeping weight AND you prefer higher-than-normal room temperature, it means you're not getting all the energy you should from the food you eat, in other words, your system is digesting food incompletely.
I do have a digestive disease myself, and at my worst before surgery + medication, I was drinking glasses of custard every day just to stay above 155 lbs; I'm a pretty tall guy, ideal weight that I'm seeing now is around 190 lbs. I gained 30 lbs in one month after the surgery.