Naked Science Forum
General Science => General Science => Topic started by: Joe Negron on 06/04/2009 19:30:02
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Joe Negron asked the Naked Scientists:
Hello Chris and the gang!
I love your show (http://www.thenakedscientists.com/HTML/podcasts/) and consider it one of the best science podcasts (http://www.thenakedscientists.com/HTML/podcasts/).
I have what may seem an odd question: do we lose weight when showering?
I have one of those body fat monitoring scales; it has a resolution of half a pound. More often than not I weigh half a pound less and have a slightly lower body fat percentage (usually one percentage point) after showering than before.
I understand that the scale is not a high precision instrument - indeed,
successive weighings will often vary a half a pound and a percentage point. However, I don't think the weight reduction can be attributed to this lack of precision because when it does vary, it's always less, never more.
The only explanation I can think of is dead skin cells. But, can we really lose approximately eight ounces of dead skin cells in the shower?
By the way, I feel compelled to point out that I do not urinate in the shower! :) Therefore, that can't be the answer either.
What do you think?
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By the way, I feel compelled to point out that I do not urinate in the shower! :) Therefore, that can't be the answer either.
I can't answer your query except to note that it seems as though your weight loss is within the accuracy of your instrument, and how do they calibrate these things?
Peeing is OK - it's best to draw the line at taking a dump though [:o]
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Well I know the body fat sensors in those scales are supposedly very inaccurate. They rely on passing an electric current through you and measuring the resistance in order to determine your body fat % (fat is more resistive than lean tissue). If you've just gotten out of the shower, you're probably still wet and therefore have less resistance to electrical currents, which leads the scale to decide that you have lower body fat than when you're dry.
I'm not sure why you lose weight. The scale probably uses springs or something like that to determine your weight. I guess if you keep the spring in the bathroom and it heats up, that could possibly effect whatever mechanism it uses to tell your weight. Also, if you take a very long and hot shower, you might lose weight in sweat. I know I've managed to lose several pounds of sweat over the course of a long run in the summer heat, but a half pound seems excessive in the shower.
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Many electronic bathroom scales use strain gauges which can be very temperature sensitive. Manufacturers of gauges try to allow for this in the choice of materials used and the construction, but even so, it may be necessary to have additional compensation curves applied in the software used to produce the reading. The resistance of the leads to and from a gauge is also temperature-dependent, and the gauges are very sensitive to this.
I'm speculating, but it is possible that to minimise costs, bathroom scale manufacturers that use strain gauges don't use the best temperature-compensating gauges, leads, and software - after all, bathroom scales are not are not, in general, a high-precision application.
Of course, this hypothesis doesn't apply if the scales are outside the bathroom, or the bathroom temperature is reasonably constant...
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Your scale's resolution shouldn't allow you to consistently pick this up, but you do lose weight anytime you aren't eating or drinking. You perspire, as mentioned by jpetruccelli, and will do so slightly more in the hot water of a shower. You also breathe out water vapor and CO2 in excess of what you inhale. But that shouldn't be more than a few grams unless your showers are really long.
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By the way, I feel compelled to point out that I do not urinate in the shower! :) Therefore, that can't be the answer either.
I can't answer your query except to note that it seems as though your weight loss is within the accuracy of your instrument, and how do they calibrate these things?
Peeing is OK - it's best to draw the line at taking a dump though [:o]
Well, I figured that if the difference was merely a random fluctuation of the scale's instrumentation, it would vary both more and less. As I stated, the difference is always less.
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Well I know the body fat sensors in those scales are supposedly very inaccurate. They rely on passing an electric current through you and measuring the resistance in order to determine your body fat % (fat is more resistive than lean tissue). If you've just gotten out of the shower, you're probably still wet and therefore have less resistance to electrical currents, which leads the scale to decide that you have lower body fat than when you're dry.
I'm not sure why you lose weight. The scale probably uses springs or something like that to determine your weight. I guess if you keep the spring in the bathroom and it heats up, that could possibly effect whatever mechanism it uses to tell your weight. Also, if you take a very long and hot shower, you might lose weight in sweat. I know I've managed to lose several pounds of sweat over the course of a long run in the summer heat, but a half pound seems excessive in the shower.
Aha! I think you have it! I take very hot showers and am often perspiring when I get out.
Regarding the amount lost, what I should have said was that the scale, if it does report a difference, reports a half pound (the resolution of the scale), or, rarely, a pound. Suppose I weigh exactly 162 lbs. before the shower. After the shower, whether due to perspiration, or whatever, I weigh 161 lbs. 12 ounces (exactly halfway between the resolution of the scale). In this case, perhaps the scale sometimes reports 162 lbs. and other times 161.5 lbs. So, if true, it's not necessarily the case that I lost 8 ounces due to perspiration or whatever.
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In my experience exactly how you stand on the scales affects the reading, after showering the skin on the bottom of your feet will have been softened which will affect how you stand on the scales and may modify the reading.
It would be better to use a two pan scale such as was used to weigh jockeys when you would be seated and balancing weights placed in the other pan
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Joe Negron asked the Naked Scientists:
Hello Chris and the gang!
I have what may seem an odd question: do we lose weight when showering?
I have one of those body fat monitoring scales; it has a resolution of half a pound. More often than not I weigh half a pound less and have a slightly lower body fat percentage (usually one percentage point) after showering than before.
I understand that the scale is not a high precision instrument - indeed,
successive weighings will often vary a half a pound and a percentage point. However, I don't think the weight reduction can be attributed to this lack of precision because when it does vary, it's always less, never more.
The only explanation I can think of is dead skin cells. But, can we really lose approximately eight ounces of dead skin cells in the shower?
By the way, I feel compelled to point out that I do not urinate in the shower! :) Therefore, that can't be the answer either.
What do you think?
Of course you lose weight when you shower. Any time you exert yourself you use up calories, i. e. more than when resting you loose weight although not much. If you do nothing for twenty-four hours you will use up 3500 calories (one pound). Showering will use up much less than that 3500 calories. You will probably not be able to measure the difference between your weight before and after the activity in the shower.
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Joe Negron asked the Naked Scientists:
Hello Chris and the gang!
Links removed.
I have what may seem an odd question: do we lose weight when showering?
I have one of those body fat monitoring scales; it has a resolution of half a pound. More often than not I weigh half a pound less and have a slightly lower body fat percentage (usually one percentage point) after showering than before.
I understand that the scale is not a high precision instrument - indeed,
successive weighings will often vary a half a pound and a percentage point. However, I don't think the weight reduction can be attributed to this lack of precision because when it does vary, it's always less, never more.
The only explanation I can think of is dead skin cells. But, can we really lose approximately eight ounces of dead skin cells in the shower?
By the way, I feel compelled to point out that I do not urinate in the shower! :) Therefore, that can't be the answer either.
What do you think?
We lose a lot of sweat, skin oils and skin cells along with a few hairs when we shower but unless you're peeing in the shower it's not going to add up to anything mesurable with a device such as that. It's probably somewhere in the milligram range.