Many of my patients are concerned and confused by day to day fluctuations in their weight. They wonder how they gained so much weight in one day. They wonder if their scale is broken. They wonder if this happens when they eat "badly." They come to me and ask, "why does my weight fluctuate so much?"
Let's review some information. If you drink two cups of water, you will weigh about one pound more. An average-sized meal weighs about one pound, so you will weigh one pound more after the meal than you did before the meal. A bowel movement can weigh one pound, so you will weigh less after using the restroom. Many people lose one pound of sweat from a one hour run, so the pound of weight lost from that workout is from the sweat. In short, there are many normal bodily functions and activities that can account for day to day weight changes.
In general, daily weights can be exasperating for most people. Besides for some very specific medical reasons, it is not necessary for people to weigh themselves daily. Many people would even benefit from rarely or never weighing themselves. Because our body uses many functions to maintain our health, our weight can shift from one day to the next.