The most promising antiobesity treatment once involved the "anti-fat hormone," leptin; its discovery led to a surge of obesity drug research. Leptin, discovered in 1994, seemed promising because it is produced by fat cells and was the first antiobesity hormone that surfaced.
The leptin hormone receptor was discovered in 1997 when a mutant strain of extremely obese mice (lacking the gene to make leptin) were able to shed their weight when given leptin. With injections of leptin, the mice's appetite decreased while their metabolic rates increased. Although researchers wondered whether all obese people would lose weight on leptin, this did not occur. It turns out that, like the mutant obese mice, there are only a few rare cases known of human obesity caused by leptin deficiency. Most people seem to become obese by eating too much and being too sedentary. The leptin discovery should provide a successful treatment for rare cases of obesity in leptin-deficient individuals who, in the past, would not have been able to lose weight.
Many people who are obese actually have higher than normal blood levels of lep-tin and are resistant to its actions. In some leptin trials, the hormone was intended to be given to overweight people, but it was found that they were leptin-resistant and their leptin levels were already very high. In fact, some obesity researchers now believe that leptin has more to do with protecting against weight loss in times of famine, than protecting against weight gain in times of plenty. When fat stores increase, so does leptin; when fat stores shrink, so does leptin. Appetite increases and metabolism decreases when leptin levels shrink, but the opposite does not occur; appetite is not suppressed when leptin increases, nor is metabolism increased. Leptin, it seems, is one of those evolutionary hormones designed to keep our species alive and protect us from starvation. Finding leptin has led obesity researchers into finding out more about how appetite, fat stores, and famine-protection mechanisms work in the body.
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