Where does the weight come from?

[Upchurch]

So, I've been on a diet for a couple of months now, which means I've been monitoring my weight pretty closely. In that time I've noticed patterns in my weight increase/decrease throughout the day and there is one patter that has me confused.

I weigh myself before going to before going to bed and then I weigh myself in the early morning when I let the dogs out. Generally, my weight goes down from, I assume, loss of water during the night due to sweat, urination, etc. I then go back to bed for maybe another half hour to an hour. When I wake up and measure again, sometimes my weight goes up without my eating or drinking anything. And it's not a fluke as it happens fairly consistantly.

Now, that mass must come from somewhere, but where? Any ideas?

[Aoidoi]

Dog hair? ;)

I just want to mention that I wonder about weight changes too. It seems odd, and I wonder if we can bribe Thirdtwin to venture a medical guess on what happens... :D

[arcticpenguin]

How good is your scale? If you put your weight on your heels vs. your toes, does the reading change?


A movie will be out soon called 21 grams (http://movies.go.com/movies/numbers/21grams_2003/). I've seen the trailer, and they state that people's bodies lose 21 grams of weight at death. :rolleyes:

[Upchurch]

Originally posted by Aoidoi
Dog hair? ;)You joke, but as much dog hair as I vacuum up every day, I wouldn't be that surprised. ;)

However, in the interest of a full picture. It also happens when I sleep in on weekends and haven't messed with the dogs between measurings. :con2:

[ceptimus]

I suspect the scales. They probably take longer to recover back to zero than you suspect.

Try this experiment: Weigh person A, after a minute, weigh the heavier person B, after a further minute reweigh person A.

If my theory is correct, my prediction is that person A will have mysteriously gained weight over the two-minute interval.

[arcticpenguin]

How big are the changes? Are we talking grams or kilograms?

[Upchurch]

We're talking as much as a pound, depending on the length of time between measurements. Also, it is a digital scale that measures to 2/10ths of a pound.

Yes, the scale measure differently if I stand on the extreme edges, but I tend to stand pretty consistantly in the same place. I've also gotten in the habit (as all good scientists should) to take several (often three) measurements per data point. Sometimes one measurement will be different. In those cases, I take up to four measurements and I've never had less than three identical readings.

[Upchurch]

Originally posted by ceptimus
I suspect the scales. They probably take longer to recover back to zero than you suspect.It's a digital scale that I believe recalibrates itself before every measure. Before you step on, you tap it and wait for the display to cycle through a series of symbols before you step on. If you step on before it's ready, it reads an error.

[Skeptoid]

Unless you're on a drastic weight reduction plan you're only going to lose a pound, maybe two, per week so weighing yourself daily is rather pointless and discouraging. Every scale is different and reacts differently to variation in temperature and humidity. The bathroom is probably the worst place in the house to use a "bathroom" scale because of this. Put the scale in another room with a hard floor and only weigh yourself once a week in the morning. Weigh yourself twice and average the results. If you're a good boy on your diet you'll be encouraged by the downward trend you see each week instead of being frustrated by daily fluctuations.

[Upchurch]

Originally posted by Skeptoid
Unless you're on a drastic weight reduction plan you're only going to lose a pound, maybe two, per week so weighing yourself daily is rather pointless and discouraging. I'm on Atkins and have lost 30 pounds over 12-13 weeks. I started measuring several times a day out of curiosity of how my body is effected throughout the day. I don't place enough ego in my physical shape that I find weight gain discouraging, espeically considering the overall success I've had. I don't find it pointless because I'm learning more about how my body works.

As I've said (well, implied), I don't take a shower between the measurements where I see the slight gain so, there is no significant change in humidity. It is possible that there might be a change in temperature, however, my second measurement often occurs before the sun comes up so I don't think there is a significant change.

[ceptimus]

Originally posted by Upchurch
It's a digital scale that I believe recalibrates itself before every measure. Before you step on, you tap it and wait for the display to cycle through a series of symbols before you step on. If you step on before it's ready, it reads an error. The scale is zeroing itself, but not recalibrating its 'gain'. Please try the experiment if you can. Use a heavy object for the test if a second person is unavailable. When the experiment is so simple to do, why bother to speculate?

Another thought. Are the scales standing on a firm floor? I've seen some very strange readings when the base of scales sinks into carpet as the load is applied. (However, don't let this idea distract you from carrying out the experiment - we must be scientific about this matter) :D

[arcticpenguin]

I think you're ready to move up to the next step. Install a scale in your bed so you can catch that weight in the act of leaving and returning.

[Walter Wayne]

Is the scale temperature and humidity sensitive. You seem to weigh more later in the morning. Just a thought.

Walt

[BTox]

Originally posted by Upchurch
I weigh myself before going to before going to bed and then I weigh myself in the early morning when I let the dogs out. Generally, my weight goes down from, I assume, loss of water during the night due to sweat, urination, etc. I then go back to bed for maybe another half hour to an hour. When I wake up and measure again, sometimes my weight goes up without my eating or drinking anything. And it's not a fluke as it happens fairly consistantly.

Now, that mass must come from somewhere, but where? Any ideas?

See what happens with that crappy Atkins diet? Weight magically re-appears ;)

Seriously, it must be variation in your scale. It is not possible to gain weight without any input (water and/or food).

[diddidit]

Originally posted by Upchurch
So, I've been on a diet for a couple of months now, which means I've been monitoring my weight pretty closely. In that time I've noticed patterns in my weight increase/decrease throughout the day and there is one patter that has me confused.

I weigh myself before going to before going to bed and then I weigh myself in the early morning when I let the dogs out. Generally, my weight goes down from, I assume, loss of water during the night due to sweat, urination, etc. I then go back to bed for maybe another half hour to an hour. When I wake up and measure again, sometimes my weight goes up without my eating or drinking anything. And it's not a fluke as it happens fairly consistantly.

Now, that mass must come from somewhere, but where? Any ideas?

Try changing the battery in the scale - weigh your funky self, change the battery, then weight yourself again. See what happens.

did, down 15 pounds in 3 weeks...

[sorgoth]

Originally posted by Upchurch
It's a digital scale that I believe recalibrates itself before every measure. Before you step on, you tap it and wait for the display to cycle through a series of symbols before you step on. If you step on before it's ready, it reads an error.

Makes me think of the old Garfield strips..."You are fat!" *Garfield stares menacingly at scale* "Umm...I mean...ERROR!"

[HarryKeogh]

the best scales are the ones in gyms and doctor's offices (the ones with the balance)

unfortunately not practical for most homes but they always give the best readings. i bought a cheap 15 dollar scale at a bath store and i get a different reading every single time i step on it.

[athon]

The answer is actually quite banal. It's primarily water.

Water balance in your body varies considerably during the day. You can vary up to several kilograms (2.2 pounds to a kilo - you figure it).

In the morning, you've retained a fair amount of water. With diets, one of the first things that happens is your body rids itself of stored water. Hence you lose a massive amount of weight in the first week of dieting, as your body adjusts to altered resources.

Athon

[MRC_Hans]

You claim that your weight goes up between two weighings in them morning. Are you SURE, you don't drink a glass of water (I ask because I would personally feel very uncomfortable going back to bed without a drink of water)?

Other sources could be, as some mention, the scale. Does temperature or humidity, in the room where the scale is, change (like turning on the heat or somebody taking a shower)?

You might actually gain weight by breathing :eek: . You breathe oxygen, and the body gets energy from burning carbohydrates, that is, carbon and hydrogen. The combustion products are carbon-dioxide and water. The carbon-dioxide is exhaled and will constitute a loss of weight, but the water stays in the body and gives an increase in weight. The net result is normally a loss of weight, but depending on diet, the amount of metabolic water can vary. Certain animals (e.g desert rats) never DRINK water, they get all their water from metabolic water.

When you get up the first time, your body wakes up, and your metabolism goes into its day gear, thus you MIGHT actually gain weight during your morning snooze. Whether a common bathroom scale can detect it is another matter ;)

Digital bathroom scales are not as precise as you may (be led to) believe. The fact that is has .2 pound resolution does not mean that it has .2 pound precision .

Hans

[wayrad]

Originally posted by MRC_Hans
You might actually gain weight by breathing :eek: . You breathe oxygen, and the body gets energy from burning carbohydrates, that is, carbon and hydrogen. The combustion products are carbon-dioxide and water. The carbon-dioxide is exhaled and will constitute a loss of weight, but the water stays in the body and gives an increase in weight. The net result is normally a loss of weight, but depending on diet, the amount of metabolic water can vary. Certain animals (e.g desert rats) never DRINK water, they get all their water from metabolic water.



Could you give an example, please? This has me curious. Best I can figure, the only way you could gain a pound by metabolizing stored glucose or glycogen would be if you respired almost a pound of the stuff and never exhaled the CO2 or excreted any of the water...but I haven't figured it out for any other substrates. What would be some possibilities to try?

[Occasional Chemist]

Originally posted by MRC_Hans

Other sources could be, as some mention, the scale. Does temperature or humidity, in the room where the scale is, change (like turning on the heat or somebody taking a shower)?


My analytical chemist's magic 8 ball says "Signs point to the scale". Also note that just because it's a digital scale, that doesn't mean that it's better. It's just easier to read.

...snipped the discussion of inhaling - I'll just remind y'all that CO2 is heavier molecule for molecule than O2...


Digital bathroom scales are not as precise as you may (be led to) believe. The fact that is has .2 pound resolution does not mean that it has .2 pound precision .


In all likelihood, the scale's precision is +/- 1 pound. The more digits, though, that the manufacturer shows, the better Joe Consumer thinks the scale is. You see this trick a lot with digital thermometers too.

edited to add: I second the call for testing this scale with a heavy object that you KNOW is not gaining or losing weight daily.

[arcticpenguin]

Originally posted by wayrad


Could you give an example, please? This has me curious. Best I can figure, the only way you could gain a pound by metabolizing stored glucose or glycogen would be if you respired almost a pound of the stuff and never exhaled the CO2 or excreted any of the water...but I haven't figured it out for any other substrates. What would be some possibilities to try?
I'm not sure if I'm buying the explanation for humans, but an example of an animal that gets its water entirely from its food is the kangaroo rat. At least, that claim was made on a TV nature show once.

[MRC_Hans]

I certainly don't think it can make you gain half a pound in an hour, though it might happen to flip the last digit on the scale.

You cannot not exhale CO2 , you would suffocate. My guess at Upchimp's weight gain is that he takes a glass of water before he goes back in for his snooze ;)

But for the mechanism :

The (approximate) atomic weights are, Hydrogen=1, Carbon=12, Oxygen=16. So when two H is metabolized, you gain 16, but when one C is metabolized you loose 12,
assuming the CO2 is exhaled while the H2O is (temporarily) retained.

So for any hydrocarbon that has at least 2 hydrogen atoms per carbon atom (like e.g. clucose), you get a metabolic weight gain.

Hans

[Michael Redman]

Originally posted by Upchurch
When I wake up and measure again, sometimes my weight goes up without my eating or drinking anything. And it's not a fluke as it happens fairly consistantly. How much does your teddy bear weigh? Maybe you're forgetting that you're holding it when you weigh yourself.

[wayrad]

Originally posted by MRC_Hans
The (approximate) atomic weights are, Hydrogen=1, Carbon=12, Oxygen=16. So when two H is metabolized, you gain 16, but when one C is metabolized you loose 12,
assuming the CO2 is exhaled while the H2O is (temporarily) retained.

So for any hydrocarbon that has at least 2 hydrogen atoms per carbon atom (like e.g. clucose), you get a metabolic weight gain.

Hans

I don't think it quite works that way if you want a balanced equation...
Here's the equation for respiration of glucose:

C6H12O6 + 6 O2 <-> 6 CO2 + 6 H2O

One mole of glucose weighs 180 g (rounding off) and requires 192 g of oxygen for its respiration, giving 372 g on the left side of the equation. It produces 372 g on the right side - 264 g of CO2 (which is mostly exhaled) and 108 g H2O (possible fates of which include being exhaled as water vapor, retained, or excreted). So you can see that there's a net loss from the organism.

Penguin - I have no doubt that desert animals get water from food. I'm sorry if my post was unclear on that.

[Occasional Chemist]

Originally posted by MRC_Hans
I certainly don't think it can make you gain half a pound in an hour, though it might happen to flip the last digit on the scale.


I think the problem with this line of reasoning is the mass of oxygen a person is expected to breathe in an hour. It's something on the order of 0.2 pounds (calculate from average lung capacity, number of breaths per minute, air as an N2/O2 mix, etc.). So unless Upchurch isn't breathing out oxygen AT ALL, his weight gain from any oxygen he keeps won't even show up on the scale. Plus, he'll blow up like a balloon. :)



The (approximate) atomic weights are, Hydrogen=1, Carbon=12, Oxygen=16. So when two H is metabolized, you gain 16, but when one C is metabolized you loose 12,
assuming the CO2 is exhaled while the H2O is (temporarily) retained.

So for any hydrocarbon that has at least 2 hydrogen atoms per carbon atom (like e.g. clucose), you get a metabolic weight gain.



But what about the oxygen that already exists in carbohydrates like glucose (C6H12O6)? If we treat the overall process like simple combustion:

C6H12O6 + 6O2 --> 6CO2 + 6H2O

If the CO2 is exhaled, your net loss is the mass of the 6 carbon atoms.

[wayrad]

Originally posted by MRC_Hans
...but when one C is metabolized you loose 12,
assuming the CO2 is exhaled ...


Here's the problem, I think - that mole of exhaled CO2 contained 36 (edited to add: oops! 32:o) g O2 in addition to the 12 g C !

[Upchurch]

Okay, I'm sold on the instrumentation error. The most likely cause of the error is due to temperature change. You'd think manufacturers could come up with a scale the compensates for factors like that.

[JSFolk]

You know, alien rectal implants are small, but dense!
Have you experienced any missing time between weigh ins?

[Brian]

Um, dad. Towel rack.

[Upchurch]

Originally posted by JSFolk

You know, alien rectal implants are small, but dense!
Have you experienced any missing time between weigh ins?Yeah, actually. I thought it was just sleep.
Originally posted by Brian
Um, dad. Towel rack. D'oh!

[Diamond]

Oh no! More Atkins dieters!

Don't you know that it's unbalanced as well as unpalatable and dull? (http://news.bbc.co.uk/1/hi/health/3128188.stm)

I mean, when my own government tells me these things - it must be true... :rolleyes:

[Occasional Chemist]

Originally posted by Upchurch
The most likely cause of the error is due to temperature change. You'd think manufacturers could come up with a scale the compensates for factors like that.

They do. But you likely don't want to pay for it. For most people a scale like yours is adequate - they weigh themselves maybe once a day at about the same time each day.

[Dr. Imago]

All excellent guesses. No other theories to add.

The only thing that I would throw in there is that, if you can afford it (and you have a pre-occupation that borders on more than just simple curiosity about this ;) ), you should invest in a balance. Electronic and spring scales are notoriously unreliable. Physician's scales seen in doctor's offices (which are essentially fancy balances), which work on mass effect, are the most reliable to weigh yourself.

http://www.homehealthdepot.com/images/HLM400.jpg

Just my 2 cents.

-TT

[MRC_Hans]

Originally posted by wayrad


Here's the problem, I think - that mole of exhaled CO2 contained 36 (edited to add: oops! 32:o) g O2 in addition to the 12 g C ! Yep! But you inhaled that O2. The whole trick is that some of the inhaled O2 stays in the form of water and an oxygen atom is heavier than a carbon atom.

Hans

[MRC_Hans]

Originally posted by Occasional Chemist


They do. But you likely don't want to pay for it. For most people a scale like yours is adequate - they weigh themselves maybe once a day at about the same time each day. Yeh, I was about to come up with the same answer. I have been constructing electronic scales in an earlier "incarnation". These things were WAY more precise, but the price was, oh, about 50 times that of a bathroom scale.

3rdTwin: Good idea! Those balances are really good, but they take up a bit of space. My best advice is weigh yourself once a day AT MOST.

Hans

[Occasional Chemist]

Originally posted by MRC_Hans
Yep! But you inhaled that O2. The whole trick is that some of the inhaled O2 stays in the form of water and an oxygen atom is heavier than a carbon atom.

I don't think you can discount the oxygen that's already present in the carbohydrate, though. Even if some of the inhaled O atoms end up in your body as water, some O atoms that were part of the original carbohydrate will be lost.

[wayrad]

Originally posted by Occasional Chemist


I don't think you can discount the oxygen that's already present in the carbohydrate, though. Even if some of the inhaled O atoms end up in your body as water, some O atoms that were part of the original carbohydrate will be lost.

Absolutely. Hans, this can be seen by using the respiration equation to construct a mass balance. Note that the same number of atoms of each element appear on the left ("before") side as on the right ("after") side, i.e. it's a balanced equation. To respire one mole (180 g) of glucose, you must inhale 6 moles (192 g) of O2 (i.e. 12 moles O). But then you must exhale 6 moles CO2 (264 g) and you only get to keep the 6 moles of water (108 g). The 18 moles of atomic oxygen originally present (6 moles in the glucose and 12 moles in the oxygen gas) is thus fully accounted for (12 moles ends up in CO2 and 6 in water). (edited to add: Note that although you end up keeping 6 moles O in the form of water, this just leaves you with the same number that was originally present in the glucose!). The 12 moles of hydrogen end up in water and are kept. The 6 moles of carbon are lost.

[arcticpenguin]

Originally posted by MRC_Hans
Yeh, I was about to come up with the same answer. I have been constructing electronic scales in an earlier "incarnation". These things were WAY more precise, but the price was, oh, about 50 times that of a bathroom scale.

3rdTwin: Good idea! Those balances are really good, but they take up a bit of space. My best advice is weigh yourself once a day AT MOST.

Hans
The problem with those snifty digital readouts is that it's so easy to mistake precision for accuracy.

[BTox]

Originally posted by wayrad
Absolutely. Hans, this can be seen by using the respiration equation to construct a mass balance. Note that the same number of atoms of each element appear on the left ("before") side as on the right ("after") side, i.e. it's a balanced equation. To respire one mole (180 g) of glucose, you must inhale 6 moles (192 g) of O2 (i.e. 12 moles O). But then you must exhale 6 moles CO2 (264 g) and you only get to keep the 6 moles of water (108 g). The 18 moles of atomic oxygen originally present (6 moles in the glucose and 12 moles in the oxygen gas) is thus fully accounted for (12 moles ends up in CO2 and 6 in water). (edited to add: Note that although you end up keeping 6 moles O in the form of water, this just leaves you with the same number that was originally present in the glucose!). The 12 moles of hydrogen end up in water and are kept. The 6 moles of carbon are lost.

Yes, this is correct, and it makes several assumptions that favor Hans' assertion. One, it assumes all the oxygen required to burn the 180 grams of glucose comes from respired air during the time in question (30 minutes to an hour). But 192 grams of oxygen is equivalent to 134 L of oxygen absorbed, and at rest a typical human only absorbs ~ 25 L of oxygen (or ~32 grams) per hour. Second, the assumption that all water stays in the body is erroneous. Respiration eliminates ~ 300 - 600 grams of water per day, and a similar amount of water is lost through evaporation from the skin.

Looking only at respiration mass flow, we absorb 25 L of oxygen per hour (32 grams), but expire 25 L of water vapor and 15 L of CO2, which nets a total weight of 44 grams (18 grams from water vapor + 26 grams of CO2), so we lose 12 grams per hour. So much for the Breathairians!

[wayrad]

Originally posted by BTox


Yes, this is correct, and it makes several assumptions that favor Hans' assertion. One, it assumes all the oxygen required to burn the 180 grams of glucose comes from respired air during the time in question (30 minutes to an hour). But 192 grams of oxygen is equivalent to 134 L of oxygen absorbed, and at rest a typical human only absorbs ~ 25 L of oxygen (or ~32 grams) per hour. Second, the assumption that all water stays in the body is erroneous. Respiration eliminates ~ 300 - 600 grams of water per day, and a similar amount of water is lost through evaporation from the skin.

Looking only at respiration mass flow, we absorb 25 L of oxygen per hour (32 grams), but expire 25 L of water vapor and 15 L of CO2, which nets a total weight of 44 grams (18 grams from water vapor + 26 grams of CO2), so we lose 12 grams per hour. So much for the Breathairians!

No the equation doesn't say what time period the process occurs in. I agree that Upchurch could not possibly respire an entire mole of glucose in that length of time. It just shows the molar ratios of glucose respired to oxygen consumed and to CO2 and O2 (drat, I meant H2O) produced. It could just as easily be one molecule of glucose being respired by the intake of 6 molecules of O2! The proportions are the same no matter what time period you use. It's simply easier to calculate the masses involved for a mole of substrate to demonstrate that there is a net loss.

Edited to add: You are absolutely correct that the assumption that all water stays in the body is not realistic, but rather a worst case scenario designed to demonstrate that there would be a weight loss even under these circumstances.

Incidentally, for anybody who is interested, I found a nice interactive tutorial on balancing equations, with examples drawn from the combustion of various substrates:
http://www.wfu.edu/~ylwong/balanceeq/combust.html

[BTox]

Originally posted by wayrad


No the equation doesn't say what time period the process occurs in. I agree that Upchurch could not possibly respire an entire mole of glucose in that length of time. It just shows the molar ratios of glucose respired to oxygen consumed and to CO2 and O2 (drat, I meant H2O) produced. It could just as easily be one molecule of glucose being respired by the intake of 6 molecules of O2! The proportions are the same no matter what time period you use. It's simply easier to calculate the masses involved for a mole of substrate to demonstrate that there is a net loss.

Yes, I know, time isn't important as the amount of oxygen required in the equation is more than compensated for by CO2 lost. And of course, my argument for insufficient oxygen absorbed to respire 1 mole of glucose in an hour cuts both ways as there is also insufficient capacity to expire the resultant CO2 (134 L) in one hour!

[MRC_Hans]

I have to admit that this metabolic weight-gain was something I read about a couple of years ago. I can't find the source any longer :( . My present explanation may be too simple; metabolism is more than oxidizing glucose, we also metabolize lipids, some of which are turned into glucuse.

I was not seriously suggesting that Upchurch gained a pound breating for an hour, just mentioning it as a curiosity.

Hans

[Dilettante]

Originally posted by MRC_Hans
You cannot not exhale CO2 , you would suffocate.

This must be a misprint. If you didn't exhale CO2 you would die.

I'm also with the scale theory. Try weighing an inanimate object before and after your nap. The weight difference should be the same as yours.

[MRC_Hans]

I wrote: You can not not etc. I know double negations are handled differently in different languages, but this is not a double negation, it is a nested negation ;)

Hans

[wayrad]

Originally posted by MRC_Hans
I have to admit that this metabolic weight-gain was something I read about a couple of years ago. I can't find the source any longer :( . My present explanation may be too simple; metabolism is more than oxidizing glucose, we also metabolize lipids, some of which are turned into glucuse.

I was not seriously suggesting that Upchurch gained a pound breating for an hour, just mentioning it as a curiosity.

Yes, it does get interesting when you consider other substrates. I looked up typical respiratory quotients (ratio of CO2 produced to O2 required) for fat (0.710) and protein (0.835). Since MW of CO2 is 44 and that of O2 is 32, back-of-the-envelope calculations indicate that using a mole of O2 to completely combust fat could result in 760 mg less CO2 going out than O2 going in!

There are a couple of practical difficulties, though. One is that at 24.45 L/mol gas at STP and 21% O2 in air, you would need to breathe 116.43 liters of air to gain that 760 mg. Using BTox’s numbers, this would take upwards of 4 hours, during which time you would have to exhale only bone-dry air and refrain from allowing any evaporation off your skin. However, I suspect that the major difficulty is that you would also have to shut down respiration of all other substrates (such as glucose in your brain) that would cause net loss of mass as CO2.

I know you were't seriously suggesting it as an explanation for Upchurch's question, but it makes an interesting thought experiment, all the same!

edited to add: I made a mistake applying Btox's number - I see now that it was 25 L O2/h, not air. So it would take closer to 1 h than 4, unless I goofed somewhere else.

[Agammamon]

I think it's obvious Upchurch. You've been on a diet for a couple of months and your body is protesting against this form of cruelty by making you go down to the fridge in the morning and then forget about it.

[EvilBob]

Maybe Upchurch had a dream that he was eating a giant marshmallow and when he woke up again his pillow was missing ;)