Healthy diets are good for teenagers. That may seem like a bit of a no-brainer--healthy diets are important for everyone, of course. But particularly in adolescents, eating low-fiber diets can lead to more fat around their middles and higher levels of inflammatory biomarkers, both of which put them at higher risk of diabetes and heart disease.
The researchers looked at 559 young people between 14 and 18 and found that, on average, they ate only a third of the recommended daily intake of fiber, and only 1% ate the full recommended intake. The teenagers who ate less fiber had higher levels of cytokines and other markers of inflammation in their blood, as well as more fat around their organs (visceral or abdominal fat) and lower levels of the protein adiponectin, which protects from inflammation.
It's not quite clear why fiber has this effect on biomarkers and body fat--it could be that those people who eat more fiber also eat a better diet and exercise more. It could also be that fiber makes people feel more full and so eat less, or that fiber makes sure that food passes through the gut more quickly.
Changing the diet of teens isn't going to be easy, because low-fiber and highly processed foods are so easily available, and high-fiber foods aren't always palatable: How many teens would pick lentil soup and bran muffins over burger and fries? However, changing diets is going to be vital to combat the obesity epidemic sweeping the developed world.