At night, I weigh 158 - the next morning, I weigh 156.5

[Lukeinva]

The latest new diet fad: Take a nap!

[DSeid]

What’s so odd about the findings in that study Gary T links to is this:

He confined 14 healthy men to a bed with a built-in scale for 16 hours. The men didn’t urinate or defecate during the study. While sleeping, they lost 1.9 g per minute, about 1/4 lb. per hour, which amounts to 2 lbs. over eight hours of sleep. While resting awake in bed, they lost 0.6 g per minute.

Metabolism is slower while asleep. Yet they lose weight faster sleeping. Sweat more? Not respire more.

Odd.

[Michael63129]

@DSeid

What’s so odd about the findings in that study Gary T links to is this:
Metabolism is slower while asleep. Yet they lose weight faster sleeping. Sweat more? Not respire more.

Odd.

Indeed; reading that makes me wonder if they got their numbers reversed.

Also, here is another source with figures for daily water loss; 6% is lost through sweat (obviously assuming “normal” conditions since this can easily be up to 10 liters in hot climates), 6% through feces, 28% through respiration and from the skin (apparently not the same as sweating; this total is also quite a bit higher than the 250 ml from my other cite, albeit only for respiration), and 60% through urination, out of a total of about 2.5 liters (5.5 pounds). Taking a third of that gives about 1.8 pounds of weight loss overnight, but again metabolism should be slower, so should sweating if you are comfortable in bed and don’t have night sweats; eliminating water lost though urine and feces (weighing yourself before going to the bathroom) reduces this to about 0.6 pounds over 8 hours.

ETA: The 0.6 gram/minute figure supposedly given for resting awake in bed comes to about 0.6 pounds over 8 hours - the same as I calculated above, thus the suspicion about reversing figures.

[DSeid]

Well I am unable to find that original article but the author did also do this one. In short what he found this time was that weight loss during sleep varies based on sleep cycle, specifically it is fastest during slow wave sleep (SWS) associated with increased autonomic tonus which apparently allows for greater water loss through the skin (sweat glands are parasympathetically innervated):

In our study, we found a positive correlation between weight loss and SWS length. Indeed, SWS is a stage when transepidermal water loss is higher due to differences in autonomous system activity favoring weight loss. 20,21,22 In support of this hypothesis, we found that higher SWS length and parasympathetic tonus (HF component of HRV) were directly related to higher overnight weight loss rates.

So sweating in sleep, not as part of reacting to environmental temperature but as result of slow wave sleep phase, seems to be the cause for the greater weight loss while sleeping.