> If you eat enough to support muscle growth of course you'll gain weight, and NO almost everyone's diet doesn't. <br> <br>Most peoples' caloric intake is higher than it should be given their level activity, which for most is pretty low. So their weight is higher than it should be and they carry more fat than they should. If you keep this typical person's diet constant, yet change his activity level to include heavy strength training, the fat will go away and will be replaced by some amount of muscle that's more than what he had before. Caloric intake essentially places an upper limit on how much muscle his body can realistically maintain, but most peoples' caloric intake can support a higher level of muscle mass than they currently enjoy. Why? Because they're sedentary. <br> <br>Activity, however, is <b>absolutely essential</b> in a way that having a "special diet" isn't. Most peoples' "normal diet" is sufficient to support <b>some</b> amount of additional muscle. <br> <br>The other thing to consider is that the guy who all of a sudden starts strength training for an hour a day, seven days as week, will probably see a <b>natural</b> increase in appetite, meaning his diet will "automatically" change (somewhat) to support the additional activity.