What causes the scale to fluctuate so much? in less than a week, i gained 4.5lb despite exercise & diet chgs. one day overate 2cups rice instead of 1.

Weight fluctuating: Depends on a variety of factors. - food intact, fluid intact clothes and time of day. Best recommendation - weigh yourself at the same time every day - ie right before a shower when you are naked. Pay attention to whether you have emptied your bladder or bowels prior to weighing yourself as that may cause some weight flucuations as well.

Water: Rapid weight gain is usually caused by water retention.

Timing is everything: Flucuations in weight occur alot due to water weight different scales being used and when you weight yourself, the layers of clothes you wear the different shoes you may have on or off. Be consistent when weighing yourself, for best results weight yourself first thing in the morning, naked, before you shower. Consistency is key!