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Yesterday, I was fasting (drinking only water until I had dinner at 9 pm). After dinner, I went back to my lab (I am a Master's student) and worked till 1:30 AM. By 1 o' clock, I was feeling quite hungry, probably because I hadn't eaten anything all day and only had a light meal for dinner. However, I didn't eat anything then and just slept. Today morning I wake up (around 9 AM) and I don't feel hungry! I could surely eat something if I wanted, but I am not feeling the acute hunger that I was feeling last night!

More generally, what could be the reason for the behavior that a human experiences acute hunger, but after sleeping for an extended period of time, he/she may no longer have the hunger. Since a passage of time has passed, one would expect the hunger to increase, which would have certainly happened if the person had not slept. Is it the case that sleeping somehow affects the overall hunger/glucose demands of the body?

I suspect that it is possible that the body's food needs could be majorly affected by the circadian clock, but I wanted an explanation to contrast the situation when one is not hungry and when one is very hungry before sleep. How can the difference between both the situations be easily trumped by the circadian rhythm's effect? (if it is the explanation!)

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  • $\begingroup$ Do u think its normal to feel hungry when we wake up? $\endgroup$ – JM97 May 23 '17 at 7:08
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    $\begingroup$ @JM97, no its not. but the interesting question then is, that it means that the hunger situation of the body before sleeping seems to have no bearing on the hunger situation post sleeping. This I feel would warrant an explanation $\endgroup$ – user1993 May 23 '17 at 7:11
  • $\begingroup$ @another'Homosapien', I have edited the question to make it more specific and non-personal (and interesting, i think!). Could you have a look? $\endgroup$ – user1993 May 23 '17 at 7:11
  • $\begingroup$ @JM97, I have tried to do now. Feel free to edit to improve it $\endgroup$ – user1993 May 23 '17 at 7:17
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    $\begingroup$ Yeah, rewording seems to have made it better. I have voted to reopen this (in fact, I voted to close as I thought I would have chance to retract my vote by the time you edit it, but this was too fast :P). And, I can answer this as soon as the question opens again :) $\endgroup$ – another 'Homo sapien' May 23 '17 at 10:56
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I will try to keep the answer as simple as possible, but feel free to point out if I make this too simple.

Well, you are not alone with this observation. This is quite a common, but rather complex, phenomenon which controls our apetite and causes us to not feel hungry after waking up.

The feeling of being hungry is under constant regulation by two antagonistic (having opposite effects) hormones:

  • leptin, released from adipose tissue, decreases our apetite and suppresses our hunger

  • ghrelin, released from stomach, does just the opoosite i.e. increases our hunger.

And guess what, these hormones are controlled through the circadian cycle. When you sleep, your body produces more leptin and stops the production of ghrelin. Why? The answer is quite obvious: because you're sleeping. While sleeping, your metabolism is lowered because your body needs to repair the damaged cells and tissues. To control metabolism, we need to control our apetite, and to control our apetite, we need to suppress our hunger. So...? When you wake up, you still have a hangover of this effect. In other words, it takes some time to change the secretion rates of leptin and ghrelin and the resulting effects.

Lets get into some analytical details now. According to Sharma et al, 2010, metabolic rate and brain temperature are lowered during non-REM sleep to deal with the damages that may have occured during time of wakefulness. In their study, the subjects were deprived of sleep for 2 nights (4 hours per night) and then allowed to sleep for next 2 nights (10 hours per night). The result? Leptin levels decreased by 18% and ghrelin levels increased by 28%. The subjects also craved for more carbs. Also, craving for salty foods increased by 45%. Overall hunger increased by 23% due to reduction in leptin levels. They also showed that people who sleep less than 5 hours have increased Body Mass Index (BMI). All this points to the fact that sleep does cause reduction in apetite and hunger. In short, don't think of missing your breakfast.

References:

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  • $\begingroup$ so if you're hungry and you can't eat, just sleep! BTW, you can't suppress hunger by sleep for long, right? $\endgroup$ – user1993 May 26 '17 at 14:11
  • $\begingroup$ Yeah, when the body really needs energy, it will cause you to wake up. Also, IMO normal sleep duration is not enough to deplete body's food reserves. "If you're hungry and you can't eat..." I must say I didn't get that :/ $\endgroup$ – another 'Homo sapien' May 26 '17 at 14:16
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    $\begingroup$ Seems you used (kinda) improper words here. I'd say if you are hungry and have nothing to eat, you can just sleep as it would 'delay' your hunger for some time. ;) $\endgroup$ – another 'Homo sapien' May 26 '17 at 16:19
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    $\begingroup$ yes, fair enough $\endgroup$ – user1993 May 26 '17 at 16:25
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    $\begingroup$ of course! just want to give it a couple days before accepting, for obvious reasons $\endgroup$ – user1993 May 26 '17 at 17:04

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