OH, I also forgot to mention. I also fear losing weight. It took me a lot of hard work to gain weight (I know, odd coming from a female living in Orange County). I have always been underweight since birth, and have problems gaining. I over-eat to try to maintain, but I hurt my stomach in the process, it is simply too small to handle the food I eat.
I have been using Boost Plus and Ensure (I rotate them, I don't want to OD on Vitamins) and then I eat 3 big meals a day, and 3 small meals between them. I got sick in May and lost the 10 pounds I busted my butt for (or my gut, pun intended).
I'm 29 and weigh 96 pounds now. So I worry about losing any weight I have now because my immune system is kind of weak. I understand the entire concept of muscle tone and how it would help me gain, but I also need the other things (even fat!).
Eventually I'll find a good dietitian (or whatever they are called) and maybe a trainer. Sadly, most around here think because of where I live that I have a money tree in my backyard - that and they sound shocked I want to gain weight.