There are two key hormones related to our weight, the first being grehlin. Released by the stomach to increase hunger, it also slows the metabolism and decreases the body's ability to burn fat, the Daily Mail reported.
The second, and the one the study focused on, is leptin. It plays a key role in regulating body weight by signalling to the brain to reduce appetite and burn more calories. As a result, it has a significant link to obesity.
Previous research has found that people who don't have leptin are more likely to have problems with their weight.
Some people even produce very high levels of it which 'overloads' the receptor in the brain that deals with it, impairing the very mechanism that should eliminate excess fat.
Researchers from the University of Michigan in the new study discovered why the brain receptor responsible for processing leptin may not work.
They found that the receptor has two 'legs' that swivel until they encounter leptin in the brain.
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One possibility is that the receptors of people who are overweight may be lacking these 'legs', so the leptin cannot bind to the brain receptor.
"Since leptin is a master regulator of appetite, understanding why resistance to its effects develops in obesity has been a major obstacle to discovering new drugs for obesity and diabetes," said Alan Saltiel, director of the Life Sciences Institute at the university.
"Developing a clear picture of how leptin can bind to its receptor may be the first step in overcoming leptin resistance," Saltiel was quoted as saying by the paper.
The study was published online in the journal Molecular Cell.