What does it mean when you lose or gain “water weight”. Is it as simple as you’ve drank a lot of water, then pee it out? Does that count as weight?
In: Biology
About 60% of your body weight is literally water. Water is very heavy–about one pound per pint, or one kilo per liter. Assuming that you way somewhere around 155 pounds, or 70 kilograms, that means you have about 90-100 pounds (40-45 kilos) of water in your body. Most of that (about 2/3) is inside your cells. The rest is in the fluid in the “cracks” between your body cells, with a small proportion (about 1/12) making up the liquid part of blood.
Your kidneys and related systems are “designed” to keep the levels of water and all the things dissolved in it pretty constant, since going too far in either direction is bad…if you have too little water, your blood pressure drops and your organs start dying because they aren’t getting nutrients. If you have too much water, it you “puff up” (called edema). If severe, water can leak out of the vessels in your lungs and you start drowning internally (no bueno).
There are lots of ways you lose water–peeing is the biggest, but sweating, the moisture in your breath, and pooping are also big ones. If you’re working out in a very hot environment, you can lose up to *10 liters a day* of water (10 kg or ~22 pounds). Luckily, your body will respond by making you incredibly incredibly thirsty, so assuming you have enough water around you will be okay. Drinking a lot of water will obviously make you gain the weight of that water, but if your kidneys are functioning well you will pee it out quite quickly.
If you’re taking drugs called diuretics that make you pee more, you can lose water too. This is used for patients that have severe edema from their heart not working, as well as to reduce blood pressure in people with hypertension.
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