text: Gain weight or muscles ? \nAnyway there are two ways:\nOne is the organic, the other in-organic.\nFor organic growth check out heredity: parents, grand parents etc., If they had been heavy built there is every chance you may yourself become so, with good diet.\nWell, inorganic way is by abusing your consumption with fatty/ high protein based diet or administering "steriods" like the WWF wrestlers. Still if your body type is 'mesomorph', you wouldn't gain weight but burn all consumed calories and eventually load your liver and kidneys. Take care. I am not a Dr / Nutritionist.