I’ve noticed this phenomenon too. It also occurs if you fast during the day, even if you regularly drink water while you are fasting.
Clearly it’s not fat (or other tissue) loss since the thermodynamics don’t add up.
So it must be water loss.
But why would you lose water weight if you are drinking water (and urinating) during the day? Common sense says that if you are fully hydrated at Time X and fully hydrated at Time Y a few hours later, any change in your weight must be due to fat (or other tissue) loss.
My hypothesis is as follows: Your body retains water in part to help process the carbohydrates, salts, and other foods you consume during the day. There is probably a mechanism in place to keep your body’s hydraulics in balance. So for example if you eat a big deli sandwich for lunch, you can expect to gain a pound or two for the next few hours as your body processes the carbohydrates, protein, fats, and salts in the sandwich. On the other hand, if you fast for a few hours (which typically happens every night), your body can let go of some some of its water since there is not much food to process.
A hormone conveniently called “antidiuretic hormone” is produced when the small intestine sends another hormone messenger, cholecystokinin, out that there are proteins and fat that need digestin’ here, because, yes, water is needed for that. The antidiuretic hormone causes the kidneys to open up holes in kidney’s filtering tubes. This forces more water to stay inside you, rather than going to the bladder and out.
But also and equally importantly, if you eat a big deli sandwich, it’s undoubtedly full of sodium. When you eat sodium, you get thirsty. The body has a very narrow percentage of sodium in your blood that it’s happy with. When there’s temporarily too much, the quickest way to solve the problem is to add water - the kidney will filter out the excess sodium and water later, but in the meantime, your thirst mechanism will be triggered to keep your blood plasma from getting too salty. If you don’t drink to even out the sodium, then even more antidiuretic hormone is released when chemical receptors on your blood vessel walls notice that there’s a bit too much sodium here. This puts water back into the bloodstream through those holes in the kidney’s filtering tubes to even out the salt/water balance that way.
This is why people are encouraged to drink more water when they’re retaining water (unless they have congestive heart failure or kidney disease). When you decrease your intake, your body compensates by retaining water. Increase your intake, and your kidneys respond by increasing urinary output. It’s all in an attempt to keep your blood plasma as close to 0.9% sodium as possible.
(This is laughably oversimplified, of course, and leaves out the whole renin-angiotensin-aldosterone regulatory system, but it’s close enough for gov’ment work and introductory understanding.)
As for the OP: yeah, the other posters have covered it. Some small amount is due to water lost to respiration and perspiration, but most of it is due to peeing and pooping first thing in the morning. My scale is accurate to within 0.2lbs, and just for fun, I sometimes weigh myself truly first thing, without using the toilet, and then again after. A pound and a half is pretty common to lose in just minutes! That’s why if your doctor is concerned about your weight/fluid balance, you’ll be instructed to weigh yourself daily on the same scale** at the same time of day**, and you only need notify her if you gain or lose more than two pounds.
I still don’t buy this for even one second, unless you are taking excretion into account; a pound of food doesn’t magically disappear when your body digests it; most food is mostly water, which will remain in your body until excreted as urine (with smaller losses from respiration and perspiration); the fats, carbohydrates and proteins will be absorbed into your body and indigestible parts passed through as feces. And again, metabolisim can’t account for that much weight loss either; even if it was all carbohydrates, you’d need to burn 2,700 calories (and not all of that would be lost through respiration as CO2 - carbohydrates form water too, which stays in your body, plus the weight of the water, using oxygen you inhaled, is much heavier than the hydrogen from the carbs). The formula for the oxidation of glucose is 6O2 + C6H12O6 = 6CO2 + 6H2O; the weight of glucose is 180 (grams per mole) while the weight of exhaled CO2 is 264 and water (remains in the body) is 108, so there is a net loss, but of only 156 grams per 180 grams of glucose, so you’d have to burn about 15% more glucose than the 2,700 calories I mentioned above. Again, this is more like an entire day’s worth of respiration, and during sleep you burn more like 500 calories (144 grams of pure glucose, taking metabolism into account).
Thus, I still think that excretion is the single biggest reason for weight “loss” after sleep, accounting for perhaps 3/4 of the total weight loss through all means.
At night, the Sun is below you, so it’s pulling on you harder. In the morning, the Sun is above you, so it’s pulling against the Earth’s gravity, making you weigh less.
(not really, the difference is negligible, but it is kind of a fun fake explanation)
No, you don’t have to burn five thousand calories to be 1.5 pounds lighter after a given period of time; you only have to get rid of 1.5 pounds of mass. It’s not all sweating; a lot of it is simply respiration, which is how your body gets rid of a lot of fat (or, more precisely, the molecules that used to be fat.) After all, where do you think the carbon in the carbon dioxide you’re exhaling comes from?
You have to burn 5,000 calories to actually have a set body weight 1.5 pounds lighter. But it’s normal for your body weight to fluctuate. I will almost certainly weigh about 1.5 pounds less tomorrow morning than I do now, and then tomorrow everning I’ll be about 1.5 pounds heavier than I was in the morning. It happens almost every single night. I weigh myself every evening and every morning, and almost never take a dump at night.
See post #25, where I calculated the weight lost due to metabolism, which is only about 1/3 of a pound for realistic calories (around 500) burned during sleep (using glucose, as the body isn’t going to burn fat during sleep unless you are dieting; of course, using fat would reduce the weight loss even more; conversely, using glycogen would free up 4 times its weight in water but that water isn’t just going to go away). Water lost during respiration won’t be that great either since the average daily loss is about 250 grams and less than a third of that is during sleep (less breathing means less water lost); similarly, sweating may account for as little as 100 ml a day in a comfortable room, and is also usually lower when asleep (unless you sleep in a hot room, but who sleeps like that, or maybe you suffer from night sweats), which all adds up to maybe half a pound of weight loss during sleep, with excretion easily accounting for the rest.
shrug All I can say is that when I weighed myself religiously, I posted similar numbers. Multiple weighings at night and in the morning, always a drop of 1-1.5 pounds. Then again, I lose massive amounts of water weight–up to 8 pounds on a long (10 mile+) run. Of course, then I am actively sweating.
Mechanical and especially electronic scales are sensitive to temperature. They try to temperature compensate them, but it is imperfect. Especially this time of year it is much colder in my bathroom in the morning than in the evening.
Pooping and peeing give instant weight loss, and it is easy to sweat a pound of water over a night.
Of course it’s excretion. The catch is, your primary excretory organ isn’t your kidneys or your bowels-- It’s your lungs. Most of the weight of the food you eat is carbon, and that carbon is almost entirely excreted in carbon dioxide by your lungs, plus a big chunk of your water excretion. Waste in urine and feces is just covering for minor impurities and inefficiencies in the system.
Is it before or after a morning bath/shower if you have one? There was a thread awhile back about people who weighed less after a bath/shower. The temperature and/or humidity of the bathroom, if the scale’s there, might make a difference. I’ve noticed that I weigh less right after I take a bath than before, although that might just be my scale.
Obviously this is not literally true. Most of the weight of the food you eat is hydrogen and oxygen, unless you eat a lot more coal than you problably should. But you exhale those elements, too.
I read your post. The fact remains I lose about a pound and a half a night and I’m not soiling my bed.
In my wrestling days, we all pretty much knew exactly how much we would “float” during the night. So, if I needed to make 112 pounds, and weighed out at 112.5 after practice before a match, I knew I’d be right on (but seriously pushing the envelope and taking a risk in regard to scale accuracy and the quirks associated with metabolism).
Even when you’re “sucked out” (lost as much water weight as you possibly can without damn near killing yourself), you’ll float down a bit at night. You’re not consuming anything, but you’re still burning stuff off (unless you stop breathing - then you only lose 24 grams ).
It’s possible that someone is surreptitiously tunneling under your property at night and raising your house with the tailings by tens of thousands of feet. Normally a homeowner would notice such a thing, but if you’re self-employed, maybe not?
This page references a study that measured about 2 lbs. weight loss overnight, with the possibility of losing up to 1 lb. through breathing and up to ½ lb. through sweating.
).