It’s hard to turn down hamburgers, French fries, potato chips and all of the other junk food that seem to call out to us. However, eating too much junk food can harm your body, particularly if you’re between the ages of 10 and 19.

“Junk food shapes adolescent brains in ways that weaken their ability to think, learn and remember. It can also make it harder to control impulsive behaviors,” said Amy Reichelt, a brain and nutrition specialist at Western University, Canada. “It may even up a teen’s risk of depression and anxiety.”

Reichelt and two other researchers found adolescents are more sensitive than any other age group to processed foods with a lot of fat and sugar. Adolescent brains are still developing the ability to assess risks and control actions. The prefrontal cortex is the part of the brain that tells us we shouldn’t eat chips all the time and helps us resist that urge. But this region is the last to mature - it doesn’t fully develop until we are in our early 20s. Meanwhile, teen brains get more active from rewards for a while. The parts of the brain that make us feel good when we do something pleasurable are fully developed by the teen years.

In fact, these regions are even more sensitive when we are young. That’s because dopamine (多巴胺), a natural chemical that lifts our mood when we experience something good, is especially active in adolescent brains. Therefore, the teen brain has two strikes against it when it comes to resisting junk food. “It has a heightened drive for rewards and reduced self-regulation,” said Reichelt.

So, what’s the best way to say no to junk food? Researchers suggest exercise. When we exercise, the brain’s reward system becomes less sensitive to food. Exercise also cause the body to make a protein that helps brain cells grow and boosts connections between the prefrontal cortex and other brain regions. The prefrontal cortex thus can work better to help us make wise decisions and control our impulses.

3D printing has many uses and limitless possibilities. 【小题1】, such as clothing and musical instruments.

But can you imagine printing food? Some scientists are trying to change the dining experience by doing this. They hope having a 3D printer in the kitchen will become as common as the microwave. 【小题2】. You simply have to select a recipe and put the raw (未处理的) food “inks” into the printer. You can also select the instructions to make the food exactly how you want it. It would be very easy to create tasty meals.

【小题3】. There would be less need for traditional growing, transporting and packaging processes as printed food would produce less waste and pollution, which benefit our environment.

【小题4】. It could take away many jobs, including those for growing, transporting and packaging food. Imagine a world where there was no need for farming or growing crops and the same tastes could be printed from a raw “food ink”. Traditional cafés and restaurants might lose business.

It is also hard to imagine a world where the joy of cooking is dead and meals can be created at the touch of a button. 【小题5】.