It's long been known that two key hormones - ghrelin and leptin - play a key role in the body's appetite and weight management. Ghrelin tells you when you're hungry, while leptin is crucial for telling the brain when you've eaten enough.
For many years, scientists thought obesity could be caused by a shortage of leptin - thinking that without adequate levels, overweight people simply never received the message they had eaten enough.
But more recent studies have shown that obese people have plenty of leptin (in fact, the fatter you are, the more of it you appear to have), but are more likely to be 'leptin-resistant'. This means the cells in the brain that should register leptin no longer 'read' the signals saying the body is full, but instead assume it is starving - no matter how much food is eaten.
Now in a further breakthrough, scientists in Germany have discovered a 'switch' in the brain which regulates the effect of the hunger suppressant leptin. They have discovered an enzyme - histone deacetylase 5 (HDAC5) - has a significant influence on the effect of the hormone.
In fact, those unable to produce the enzymes, were leptin resistant. Remarkably, activating the hormone reversed the effect - causing weight loss.