Leptin -- not for rodents alone
There are three reasons to suspect that leptin may work in people somewhat as it does in rodents. First, the leptin molecule is quite similar in rodents and people. Second, the male rats Peter Shizgal's team used also resemble many people: he describes them as "middle-aged couch potatoes; they get free food, with small cages, little exercise. When they get older, they get wider, just like people."
Third, a study reported in October, 1999, found that leptin made dieting more effective (see "Recombinant Leptin... " in the bibliography).
The researchers tracked 73 obese people who agreed to take a dummy drug or one of four leptin dosages. After 24 weeks, subjects getting placebo had lost 0.4 kilos, on average, while those getting the highest dosage of leptin lost 7.1 kilos. More than 95 percent of the weight lost among those getting the two highest doses came from fat tissue.
Although many patients in the highest leptin dosage dropped out of the study, Andrew Greenberg, an expert in obesity from Tufts University, and one of the study authors, says he'd expect many people who lost weight would want to continue taking the drug, even though it must be injected.
Lotta hurdles remain
Is leptin the magic bullet against obesity? Not exactly. It looks good in tests so far, but:
Many people are resistant to leptin for one reason or another, and might not benefit from taking it as a drug. Problems can arise with the carrier molecules needed to get leptin into the brain, or with receptors needed to get the signal into the hypothalamus.
The version of leptin that Greenberg and colleagues used has already been supplanted by a newer version, so Food and Drug Administration approval is probably several years away.
Anything as essential as feeding behavior is likely controlled by multiple systems, and tricking one signal may not be enough. "Leptin is one of the factors that regulate body weight," says Greenberg, "but I'd not hang my hat on leptin alone."
You might have to take the drug forever. "That's a big question," says Greenberg. "A lot of people think it will have to be used like high-blood pressure medications, taken for the rest of your life." He hopes that if leptin ever reaches the market, it might be possible to wean patients from it after they've lost weight.
Before you reach for that syringe of leptin, might you win your battle of the bulge with a simple swallow-a-day?