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Exercise? Eat Right? How ‘Bout That New Hormone?

Cathy Nonas, head of the weight-loss clinic at St. Luke’s-Roosevelt Hospital, has been hearing the question all week, ever since scientists revealed that a new protein was turning fat mice into thin mice.

“So,” her food-deprived clients are gleefully asking, “does this mean your business is dead?”

It’s hard to blame them, of course, given last week’s euphoria over the new study, which claimed that a pack of New York mice had lost 30 percent of their body fat, following injections with a newly discovered hormone called leptin.

As if to whet the appetite of every potbellied American, researchers even released photos of an obese, untreated mouse - name OB 11, as in obese - lying next to a svelte, leptin-treated beauty named OB 1.

No rodent ever looked so fine.

But as with all scientific “breakthroughs,” it’s important to read the fine print, cautions Nonas and other obesity experts.

“First of all, it is not at all clear that everybody can be helped by this,” said Nonas, who added that exercise and a healthy diet remain the only universally accepted fat fighters.

Second, and perhaps more important, the clinical testing has so far been limited only to mice. Human trials are not expected to begin for another year, and even then it will probably be several more years before regulators are able to determine if leptin is safe for human consumption.

Still, the discovery has stirred more than a little excitement, even in normally staid academic circles, where breakthroughs are usually viewed more with suspicion than elation.

“When I went to see the mice, I was astonished,” said Dr. Jeffrey Friedman, recalling the day last April that he and his colleagues at the Howard Hughes Medical Institute at Rockefeller University in Manhattan, where much of the research was based, first began to see the results of their testing.

Jeff Halaas, a graduate student at the institute whose job it was to care for the mice, vividly recalls the day. It was April 10, 1995.

“I remember having to restrain myself from overly interpreting the results, but as I weighed each mouse I noticed that all had lost about 10 percent of their body weight, and that was in just five days,” said Halaas. “I thought this can’t be real. They must be sick.”

They were not sick. In fact, if anything, they were healthier. Later research would show that in addition to shedding pounds, the obese mice were also being cured of diabetes, which had been present in all of them.

The conclusion was inescapable: Those mice that were receiving the protein leptin - named from the Greek root leptos, meaning thin - were eating less, exercising more and losing weight and not just any weight. Unlike crash-dieting humans, the disappearing girth was all from lost fat cells, not lean muscle tissue.

For now, however, no one is urging caution more than Friedman and his colleagues at Rockefeller University.

Researchers aren’t even sure how leptin works, although they suspect it must have some effect on the region of the brain that sets the body’s metabolic rate.