My trainer tells me that muscle weighs as much as fat (a pound is a pound is a pound) but that since it takes up less room than fat, when one works out they add muscle which can account for a weight gain. He also tells me that a person's weight is only part of a total equation~ that if you really want to measure something, measure body fat percentage. That gives you a more realistic perspective on the changes you are making.... and gives you a better gauge on how healthy you are becoming! (I believe everything this man tells me because he was Mr Colorado 4 years in a row, is 39 and looks absolutely amazing!) Good luck and don't get discouraged! I WISH I weighed 145lbs! LOL.... someday~