JUNK food may seem like an addictive drug because it is. In rats, at least, too much fatty food raises the threshold for feelings of satisfaction, sparking a cycle of compulsive overeating.
In people, addictive drugs desensitise the brain by raising the threshold of 鈥渞eward鈥� activity that is needed to feel satisfied: more drug is needed to achieve the same effect. and colleagues at the Scripps Research Institute in Jupiter, Florida, wondered if fatty foods might also cause desensitisation.
They used electrodes to measure the sensitivity of rats鈥� brains to reward activity. Some ate normal rat food while others had limited or unlimited access to junk foods, tasty to both rats and humans. After 40 days, the brains of those that ate junk freely were less sensitive than those in the other groups. They were also obese.
Advertisement
All the rats learned that a flash of light led to a painful electric shock. Rather than try to avoid the shock when the light came on, 鈥渁ddicted鈥� rats just carried on eating. Like drug-addicted humans, they also had fewer receptors for the reward chemical dopamine (Nature Neuroscience, ).