Ghrelin and leptin are hormones, produced by your fat cells. Ghrelin says you're hungry. Leptin says you're full. They have an understanding and they take turns.
Ghrelin is produced by cells in your stomach lining and in your pancreas. High levels of ghrelin tell the brain it's time to eat.
Ghrelin acts on the hypothalamus, which is the part of your brain which controls appetite. You get hungry. As you may have deduced, ghrelin levels increase before mealtimes and drop after you've eaten.
As ghrelin levels go down, leptin levels go up. Leptin also affects the hypothalamus, telling it to reduce your appetite because you have enough fat for now, thanks.
Leptin is in your bloodstream, and the amount of body fat you have determines how much leptin you have. If you accumulate more fat, you'll also produce more leptin.
Leptin is produced in your adipose tissue (the fat in your abdomen). It is an adipose derived hormone, a hormone that controls energy intake through appetite and energy expenditure via your metabolism. Leptin also triggers ghrelin.
If you've ever struggled with your weight, it may look like ghrelin is the Bad Guy and leptin is the Good Guy.
As usual, it ain't that simple.
Leptin is actually more likely to make it harder for you to lose weight.
Let's say you're on a diet. You're trying to be sensible about it and things are going fairly well. Your fat stores are diminishing -- that's the whole idea, right?
But when those fat stores dwindle, so does your leptin. Since leptin is what puts the brakes on your appetite, as leptin decreases and ghrelin increases, those brakes commence to slip.
Your hypothalamus isn't listening to your desire to be able get into your old clothes. Instead it's attending to the seesaw of leptin and ghrelin and your appetite begins to rise.
Your will power begins to slip, along with the brakes. It's harder to stay out of the refrigerator.
Your brain isn't co-operating, in fact it's stacking the deck against you.
You give in to temptation and chow down. Fat levels begin to rise.
Leptin rises along with your fat.