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.
It is quite clear that leptins will be a large part of obesity research in the future. The sad reality though is that drugs will be used to target their manipulation. My prediction is that although the drugs will likely work, they will have serious consequences that will outweigh their short-term benefits. However, obesity is a multi billion-dollar business, which is a strong incentive for the development of these medications.