Discovered in 1999, here is what we know so far about the function of this metabolic hormone:
Ghrelin is a hormone secreted by the stomach. Like leptin, it acts on the hypothalamus but in the case of ghrelin it increases appetite rather than decreases it (as leptin does).
The levels of ghrelin appear to be regulated throughout the day and are closely correlated with meal time (levels of ghrelin are highest just before a meal).
In one study, when people were given ghrelin injections and then offered a buffet meal, they ate 30% more than normal.
It is believed that one of the main reasons why people tend to put lost weight back on after a diet is because ghrelin levels increase dramatically after a diet. This results in uncontrollable hunger and eventually over-eating by the dieter.
Too much ghrelin means too much appetite. Thin people tend to produce more of a counter-balancing hormone called Peptide YY3-36 than obese people, which indicates that obesity is more of a metabolic disorder than was first thought. Peptide YY3-36 is also produced by the stomach cells and has the effect of reducing ghrelin secretion. It is possible to increase the body's production of Peptide YY3-36 by having small, frequent meals.
Eating 5 small meals a day (think 3 meals and 2 snacks) provides the stomach with small amounts of food in it throughout the day, which then stimulates secretion of Peptide YY3-36 and which in turn, reduces ghrelin secretion and keeps hunger reduced.
And sleep! Sleep loss increases this hunger hormone so your appetite increases, and decreases it's metabolic opposite, leptin, which suppresses appetite. Sleep loss also increases the production of the stress hormone cortisol, which is lipogenic - meaning it stimulates your body to make fat.
So, did your mother tell you to eat at mealtimes and go to bed at bedtime? Did she provide you a small nutritious snack at snacktime? (All good common sense, btw, and now supported by science.)
But my mother didn't. Maybe that's why she is now an insulin dependant diabetic and I think I must have been headed down the same path. I grew up in a family that ate whenever and whatever, and only slept when we were too tired to keep our eyes open. Mom often stayed up till 2am or later. I think she must have felt 'progressive', not to be following any 'old-fashioned ideas' about bedtimes or naps or mealtimes. We are all paying the price now, though.