<Laughing> As someone who IS anorexic, and who comes from a very medical/sciency background I know of 4 very proven ways to gain weight if your thyroid isn't giving you a hand. Note : These are 4 very different diets. Diet, being defined as it's actual meaning, what one eats on a regular basis.
- Nutrient rich diet
- Calorie rich diet
- Add aspartame to you diet
- Starvation
* A combination of any of the above
Starvation works on everyone, but it's rather unhealthy, and can be life threatening if you damage your heart muscle or other organs. Essentially, you trick your metabolism into thinking you're living in a natural disaster, and it has to hoard every calorie it comes across. So at every meal, you don't eat enough. You leave feeling hungry. You skip meals. You exercise without replacing the calories you've burned, and without replacing the proteins to repair your muscles. You'll lose weight to begin with, but if you do it long enough, you'll grind your metabolism to a halt. I would ONLY do this under constant and competent medical supervision, although most of america does this to try and lose weight. Go figure.
Aspartame is a chemical that was invented when a microbiologist got curious as to why bananas in milk tasted sweeter then either the milk or the bananas separately. (My mum was his lab assistant.) Aspartame is sweet, but actually has NO calories, so like starving...it tends to be used for weight loss, even though it has the opposite effect. After several decades of research it has been proven that aspartame actually makes cell membranes less permeable. This has two effects: 1)What's already there has a harder time leaving...so, for example, fat cells are less able release their calories and shrink. 2)It creates a bit of mini-starvation (because it affects ALL cell membranes, so the cells aren't able to get all the nutrients they need, and the body hoards more calories. You can find aspartame in nearly any product labeled "Diet". Like diet pepsi, diet coke, and most "fake" sugar packets. Splenda, btw, is NOT aspartame.
A calorie rich and a nutrient rich diet are different. For calorie rich think McDonalds & cheesecake, for nutrient rich think sushi &/or rich green vegetables.
Some people lose on one, gain on the other...others the opposite...others have to combine the two to gain/lose. It all depends on your own personal body-type (your sound ectomorphic to me), metabolism, activity levels, etc.
My DH is a body builder, and when he's in training trying to gain he drinks a 4000 calorie shake with every meal. It consists largely of protein powder, peanut butter, & icecream...so it is both calorie and nutrient rich. He finds that works best with his system.
I personally lose weight on a nutrient & calorie rich diet (although I've never drunk the shake)...in large part because I starved myself for so long...but also because I'm really really active. Sadly enough, I do best if I have a PB&J sandwich on white bread WITH every meal. Yuck.
My SIL loses weight on a nutrient rich diet, but is "prescribed" one bag of McDonalds french fries a day, because she'll gain (or stay even) with a calorie rich diet. She also does the peanut butter thing to gain weight.
Anyhow...the point being...that different things work for different people. I'd save starving and aspartame, and see if either calories or nutrients or a combo of the two can help you out.
I'd ALSO get your thyroid checked. I can never remember if it's hyperthyroidism or hypothyroidism that causes weight loss...but it's a good thing to have checked out.
Gd'luck!