To my mind, nowadays teenagers are not as healthy as 50 years ago. It is because of the fast-food, the pernicious habits etc. Lots of teenagers computer addicted and don't walking and doing sports. Nowadays many young people are overweight or suffer from different diseases as a result of wrong food and lifestyle.
Firstly, teens today eat lots of harmful food, with a lot of carbohydrates and fats. Many kids and teens prefer McDonalds instead of home meal. Actually, teens usually ignore their parents' advice to eat more fruits, vegetables and dairy products. Secondly, nowadays teenagers often smoke, drink alcohol and take drugs. It breaks down their health, this is compounded by polluted water and genetically modified food. Fifty years ago the situation on our planet was better, there were not so much junk food in stores and teens preferred to spend time on the streets.
In conclusion I would like to say we have to pay more attention to our health. I suppose if we will change our lifestyle, we'll be healthy.