WE HUMANS have evolved to fatten ourselves up when food is abundant, so we can make it through the lean times. It is this tendency, the theory goes, that has been our downfall in recent decades as shops and restaurants have filled with cheap, abundant, energy-rich food. Without the lean times, the world westerners inhabit has become 鈥渙besogenic鈥� and the outcome is all too obvious: 30 per cent of US adults are obese, and the number who are overweight has tripled in 20 years.
There is no shortage of potential solutions, from raising the price of food to persuading people to exercise, most of which are unacceptable for one reason or another. The great hope is for a technical fix, a medical intervention that will stop obesity in its tracks until we can adapt to our new environment. Up to now, the only reliable way to shed weight has been through surgery, too drastic for most people, so news that two alternatives are nearing market is of real interest.
One is a vaccine against ghrelin, a hormone that tells the brain you are hungry. The second is a drug that binds to cannabinoid receptors in the brain, blocking the craving for food (see 鈥淲ill the fat vaccine help dieters shed pounds?鈥�). Both demonstrate our new-found expertise in targeting individual circuits within the brain.
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It would be premature to get too excited about these compounds until they have been more widely tested. The first candidate hormone for modifying appetite, leptin, turned out to be a damp squib. Also, if people are going to take these substances for long periods, their side effects will have to be minimal.
Yet one thing sets these substances apart. Almost all past weight-loss drugs have worked by stopping the absorption of nutrients in the gut or by boosting metabolism to burn off fat. Both allowed people to eat pretty much as usual. By contrast, the new approaches are designed to lower the desire for food.
鈥淭he great hope is for a technical fix that will stop obesity in its tracks until we can adapt to our environment鈥�
If the drugs do prove safe for large numbers of people the consequences could be fascinating. Demand for food would fall, which would ease pressure to increase production down on the farm. 鈥淪upersize鈥� meals would fall from fashion as smaller portions became a virtue. It might even signal the beginning of the end of the obesogenic environment.
This is all highly speculative, but hunger and greed are such central human impulses that manipulating them at this most basic level is bound to have major ramifications. Now, where is the brain circuit that controls the desire to exercise鈥�?
