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The "obesity hormone" Leptin appears to reduce cravings
for sweet foods by targeting taste receptors on the tongue. Therefore,
it is possible that a lack of leptin, or the body's failure to respond
to the hormone due to defects in leptin receptors, may contribute
to the so-called 'sweet tooth' that affects so many people.
Leptin, a hormone produced by fat cells,
is involved in weight regulation. It is thought that
the hormone signals the brain when fat cells are "full,"
but exactly how the hormone controls weight is not entirely clear.
The findings suggest that the tongue "is a...target for leptin,
and that leptin may be a sweet-sensing modulator (suppressor) that
may take part in regulation of food intake," Dr. Kirio Kawai
of Tokyo Medical and Dental University in Japan, and colleagues
report.
The results may explain why obese animals and humans without leptin,
or with defective leptin receptors, become obese.
Variation in leptin, or leptin receptors,
may determine why some people are more likely to eat calorie-rich
sweet foods. Although prior studies have found that obese
individuals often have too much, not too little leptin, they may
have lost their sensitivity to the hormone and become leptin-resistant,
in the same manner as so many people become insulin resistant.
To investigate the effects of leptin on taste buds, researchers
injected a group of healthy mice with leptin and gauged their reactions
to sweet, salty, sour, and bitter substances. The mice were less
interested in sweet tastes such as sucrose and saccharin after the
injection but their reactions to other tastes were unaffected.
In another part of their experiment, a separate group of mice were
bred to become diabetic and to have defective leptin receptors on
their cells. These mice did not appear to be less interested in
sweet foods even after they were injected with the hormone.
Proceedings of the National Academy
of Sciences 26, 2000;97:11044-11049.
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