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Some of us really are addicted to food

发布时间:2019-03-02 02:15:07来源:未知点击:

By Roxanne Khamsi A key appetite-suppressing hormone called leptin might limit hunger by making food appear less delectable. The finding provides more evidence that food addiction has a real biological basis and points to new ways to treat obesity, according to researchers. This influence of leptin was discovered during brain scans of two teenagers who completely lack the hormone. Parts of their brains reacted more strongly to bland foods than the brains of people with the hormone, suggesting the hormone suppresses appetite by dampening our perception of how appetising certain foods are. Under normal circumstances, our body’s fat cells churn out leptin, which travels through the blood to the brain where it reduces hunger. Studies suggest that the brains of obese individuals might become insensitive to the hormone. Sadaf Farooqi at the University of Cambridge, UK, and her colleagues came across two obese teens with another problem: they have an extremely rare genetic disorder that prevents them from producing leptin in the first place. Farooqi says she knows of only 12 people in the world that have this congenital problem. Without leptin, the two teens wanted to eat non-stop. The boy weighed 103 kilograms by age 14 and the girl weighed 128 kilograms at 19 years old. As part of the study, the researchers asked them to rate how much they liked various foods, ranging from chocolate cake to broccoli, and discovered that they rated bland foods unusually highly. Using functional magnetic resonance imaging (fMRI) technology, they then observed how the teens’ brains responded to images of such foods. Both the boy’s and girl’s brain responded similarly to the food images regardless of whether they had eaten or not. Moreover, the images provoked a strong reaction in the nucleus accumbens, a brain region thought to drive drug addiction. Healthy control subjects included in the study also had this brain response – but only on an empty stomach. Farooqi then began treating the two leptin-deficient teens with the hormone and tested their brain response to various foods one week later. After receiving leptin therapy, the nucleus accumbens of the subjects only became activated by foods when they had not eaten for several hours. The patients also changed their mind about bland foods such as broccoli and cauliflower, giving them a much lower rating than before. But they still rated cake and other goodies highly. “Why it should be cake and not broccoli, we don’t know,” says Farooqi. With long-term treatment, the teens no longer craved food non-stop and eventually slimmed down to a normal bodyweight. For example, after one year of receiving leptin, the boy weighed about 50 kilograms. “The finding should encourage a more sympathetic attitude [towards] people with weight problems,” Farooqi says. An understanding that we have an in-built biological liking for certain foods may explain why some people are more prone to crave them. Leptin researcher Jenni Harvey at the University of Dundee, UK, says the new findings improve our understanding of the hormone’s influence. But she adds that other physiological pathways can influence how rewarded we feel by certain foods. Signalling molecules such as cannabinoids, for example, also appear to manipulate our food cravings. Farooqi notes that leptin might influence the brain indirectly by triggering a cascade of reactions. So while most obese individuals produce sufficient amounts of leptin, they might possess altered versions of other signalling molecules further along this pathway. As a result, leptin’s message might not get through to the brain. Farooqi suggests that scientists should look to see if this is the case as it could point to new drug targets to fight obesity. Journal reference: Science, DOI: