A hormone that has a central role in fat metabolism. Leptin was
originally thought to be a signal to lose weight but it may, instead, be a signal
to the brain that there is fat on the body.
H ugely obese children have been found who have an inability to lose weight due
to a genetic inability to produce leptin. Injections of leptin have had dramatic
weight loss effects. It appears that, if one cannot make leptin, the brain thinks
there is no fat and spurs the person on to eat more and more in a futile effort
to get the leptin signal that fat is present. However, the effect of leptin on people
who are obese but can make leptin normally appears to be different.
A study of leptin published in the Journal of the American Medical Association
(JAMA) in 1999 returned somewhat disappointing results. It involved 54 people of
normal weight and 73 who were obese. All injected themselves daily with leptin or,
as a control, with saline (saltwater) for a month. Then the study continued with
the obese subjects to assess leptin's ability to induce weight loss. The obese patients
were given a weight-loss diet. There was little effect of leptin except at the highest
dose tested, when 2 of 8 patients lost about 35 pounds in 24 weeks. The others lost
much less and one gained weight. The 8 people on the highest dose of leptin were
the last of a group of 18 patients who had been assigned to take it; the rest dropped
out after a month of taking leptin because they could not stand to inject themselves
with several tablespoons a day of a substance that irritated their skin and was
painful to administer. The future of leptin in weight regulation remains to be determined.
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