Sleep plays an important role in weight control.  Ghrelin is a hormone that plays an important role in the regulation of appetite.21  

Research has found that partial sleep deprivation was associated with a decrease in plasma levels of leptin and an accompanying increase in plasma levels of ghrelin.  Subjective ratings of hunger and appetite also increased. 

Moreover, a remarkable correlation was found between the increase in hunger and the increase in the ghrelin/leptin ratio.  Thus the neuroendocrine regulation of appetite and food intake appears to be influenced by how long a person sleeps.  Studies show that not enough sleep could lead to obesity.22-23

Restricting sleep will in turn boost ghrelin, a hormone that makes us feel hungry.  At the same time, lack of sleep suppresses another hormone, leptin, which helps to make us feel full.  It is probable that a lack of sleep is contributing to the increasing obesity rates in America.24

Ghrelin also plays an important role in carbohydrate and lipid metabolism and, possibly, heart function, immune functions, and cell proliferation.  It promotes slow-wave sleep (SWS, non-REM sleep stages three and four). 

Ghrelin also stimulates a growth hormone.25   Researchers have found that ghrelin levels increase during the early part of the night, with highest levels in the evening and early morning before two a.m.  There is then a decrease in the morning.  The nocturnal increase was blunted during sleep deprivation, and ghrelin levels increased only slightly until the early morning.  The secretion of ghrelin during the first hours of sleep correlated positively with peak human growth hormone concentrations.26