IS JUNK FOOD ADDICTIVE?

Scientist Paul Johnson of the Scripps Research Institute had a very serious goal when they decided to feed a lot of junk food to a group of rats. They wanted to understand what happened in the brains of obese (very fat) people.

They observed that the more junk food the rats ate, the more they wanted and that the brain chemistry behind obesity and serious drug addiction seemed to be very similar.

In their experiment the scientists studied the “pleasure centre” of rat’s brains. These centres are a complicated network of nerve cells, which perform as a sort of reward system in the bodies of many mammals.

If the animal becomes active or eats, the cells reward it by releasing chemicals into the body that make it feel good. And when the body feels good, the animal or person will want to do the behaviour again.

However, pleasure centres can release chemicals in less healthy ways too. Strong drugs like cocaine or heroin can prompt the process and they can cause the pleasurable chemicals to be released.

One rat group was fed junk, like fatty and sugary cheesecake, burgers and crisps, while the other group received a nutritious diet.

Very quickly it was seen that the rats eating healthy food took in only half the calories of their junk-food-eating counterparts, who just ate more and more.

To find out why this happened, a way of artificially stimulating the rat’s pleasure centres was devised. A small electrical charge was sent to these centres when the rats ran round and round on an exercise wheel. The more the rats ran, the more pleasure they received.

The junk food eating rats more and more suggesting that they need more stimulation to feel good compared with rats on a healthy diet. In the other words, their pleasure centres were becoming less sensitive and the junk food didn’t make them feel good unless they kept consuming it.

Kenny and Johnson also found that the effects were very hard to reserve in the ‘addicted’ rats. After they took away the junk food and the offered the rats a nutritious, normal diet, the fat rats refused to eat. They starved themselves for up to two weeks afterwards.

Such experiments may point towards an understanding of how chemicals in the brain contribute to obesity and how we may be able to help people avoid it and all its health problems.