A natural fat-buster that made headlines last month for slimming down overweight mice may not do the same for really obese people, new research suggests.
Scientists found evidence that very fat people already have high levels of that substance in their bodies, maybe 20 to 30 times the amount found in slender people.
So injecting more may not help at all, says researcher Bradford Hamilton.
But another scientist who studies the substance disagreed, saying the new findings may just mean that the obese need more of the stuff than other people to control their weight.
The substance, called leptin, is produced by fat tissue. Mouse studies suggest it is a messenger to the brain that lets animals keep a relatively constant weight.
Scientists say many processes, biological and social, influence obesity, and leptin is not the total answer.