thank you for your suggestions.
As your partner is eating right but still losing weight, and all the blood tests have come back fine (apart from the liver), I would suggest that he gets his stools checked out for any possible signs of parasitic worms.
Having a tapeworm for example, a person will eat and eat and still lose weight. This can be picked up easily from undercooked meat mainly pork.
Make sure that any meat he eats is thoroughly cooked.
The doctor says he needs to gain weight. His metabolism is too fast. So he needs something to slow it down that is why I asked if marijuana might be a good idea. The diabetes would present itself Not due to weight gain but due to the increased liver damage (if he didn't change his lifestyle). Increased liver damage would massively affect the balance of insulin in his blood stream. This is what would cause the diabetes. He is asian and the family members that have type 2 diabetes were advised to change their diet not to loose weight since they were not overweight.
His blood test came back negative for thyroid problems. He doesn't drink alcohol and he used to eat a ton and not gain any weight. He has lost 20lbs. of muscle (which is what his body will keep) since December 2011. His doctor wants him to gain as much weight as he can. His fat percentage is around 4% ... this is without exercising. Doc said no sugar, caffeine, spicy foods, red meat, and eggs. Pretty much a vegetarian that eats fish and chicken. He stopped all junk food of all sorts one month ago because that is when it got really bad.
I suggest your partner asks his doctor to refer him to a dietician for advice on what he should or should not be eating, how much and how frequently.
I am surprised that the doctor did not give him any advice with regard to what your partner should be doing or not doing to get better.
A fast metabolism can also be from an overactive thyroid, has he had a blood test for this?
When you say your partner is predisposed to type 2 diabetes, I presume you mean that he is glucose intolerant?
Like Anonymouse88 points out that your partner is in the normal range of his BMI level, I would not worry about gaining weight. Taking any type of drug without his doctor's approval is not a good idea.
Tell him not to eat junk foods and to keep off alcohol and fizzy drinks and high carbohydrate foods. He needs to eat light meals (not fried) little and often. His dietician will be able to help with educating him with regard to his diet.
Make sure he also drinks plenty of water 2-3 litres throughout the day is what is usually recommended, so that he does not become dehydrated.
I don't think that's a good idea. Stoners gain weight because of increased appetite, but if he's predisposed towards type 2 diabetes, he needs to be careful about what he eats to gain weight. Does his doctor want him to gain? His BMI is currently 18.5, which is still in the normal range. He should definitely avoid alcohol, and be careful with any drug that is metabolized by his liver. I'd ask the doctor if even things like tylenol should be off limits for now. Thankfully, the liver is probably the organ with the most regenerative ability, so if he doesn't stress it, it has a much better chance of getting better than a damaged kidney might.
If he does need to gain weight, then he might look into something like Ensure, TwoCal, or Boost to help gain weight in a balanced way. An anti-nausea drug that's safe for people with bad livers might also be warranted.