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NOVA scienceNOW: Obesity

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Scientists discuss leptin, a hormone made in the body's fat cells. Leptin is involved in appetite—when the brain detects low levels of leptin, it causes a person to feel hungry. However, mutations can interfere with the delivery of leptin's signal to the brain. When the body produces little or no leptin or when leptin receptors are nonfunctional, the brain never receives the signal that the body has sufficient amounts of fat. As a result, the brain continues to prompt the person to keep eating. Researchers have found that humans and other animals with low leptin levels or a diminished ability to detect leptin tend to become obese.

This NOVA scienceNOW segment:

• discusses that most adults have a "set point"—a stable, maintainable weight that fluctuates very little. This set point is different for different people.

• points out that leptin may affect appetite by turning off neural circuits in the brain that stimulate appetite and by turning on neural circuits that allow one to feel satiated.

• explains that the MC4R receptor is faulty or nonfunctioning in some obese people, and that one in 1,000 people may carry this MC4R mutation.

• states that mice that do not produce leptin are obese.

• notes that it is important to try to stay at the lower end of one's optimal weight range, to exercise regularly, eat a heart-healthy diet, and recognize that for some people, maintaining a healthy weight is more difficult than for others.

Taping Rights: Can be used up to one year after the program is taped off the air.