A lot of that may be water weight. A gallon of water weighs about 8 lbs. (give or take). I lost 7lbs. one day doing a 4 1/2 hour, 105 degree, 100 mile bike ride. I was drinking all the water I could stand, but didn't keep up with what I was losing.I just started going to the gym off and on for about 3 months, I had been taking it pretty easy though until two weeks ago after I was healed up from ny knee surgery! I have my mind set on loosing weight and getting in shape. I've been mostly lifting 3-5 times a week, but yesterday(Thursday) decided to go to just do cardio, on wednsday night I weighed my self at 266.5 (yes im a fatass)and by thursday afternoon after doing cardio and the steam room I weighed myself at 262.25, a loss of 4.25 pounds with in a day, it blew my freaking mind! Now I'm gunna start doing cardio 2-3 times a week with my regular 3-5 day of lifting.