Huh... so actually obese animals have TOO MUCH leptin, but their brains aren't efficient in detecting it any more? Like insulin sensitivity. That's what makes this report about the former Biggest Loser winners so interesting... they are re-gaining weight and have almost zero leptin. Presumably they know all about the benefits of exercising and avoiding sugar etc.

It does sound just like insulin sensitivity. 

And yes, the Biggest Loser report is then quite confusing...

http://pandawhale.com/post/71736/after-the-biggest-loser-their-bodies-fought-to-regain-weight

...since, as you said, they know all about nutrition and exercise. 

What is Leptin Resistance?

Leptin given to animals promotes weight loss and satiation, but in obese humans it does not promote significant weight loss (R).

Obese humans have high levels of leptin, even though leptin is supposed to cause satiety, which suggests that leptin resistance causes human obesity (R).

Leptin resistance is when leptin doesn’t work as well to decrease appetite or increase energy expenditure.

Leptin resistance is now believed to be the leading driver of fat gain in humans (R).

Because fat cells produce leptin in proportion to our size, obese people also have very high levels of leptin (R), but it doesn’t perform its job the way it’s supposed to (R).

Leptin resistance leads to increased appetite and decreased energy expenditure.