Teenagers are a mystery to the adult world.

Even when my own kids were teenagers, it was hard to know exactly what their life was like. What parts of their life did they love and what parts of their day were horrid?

Sometimes there was no telling.

Even more so today, as those days are receding into the rear view mirror, I have little conception of what the modern teenager deals with.

Now we read stories of internet bullying, sexting, body image issues, drugs, gadget-filled lives, rebellion, drama and the search for identity. We can relate – sort of.

We were all once teenagers, notwithstanding the evidence of our now stodgy auras to the contrary.

After all, Baby Boomers still rock out on 1960s tunes and the extended adolescence of 20-somethings blur the line of boys to men. And everybody is paying on student (or parent) loans.

A recent study of adolescent eating and physical activity behaviors showed that it is impossible to generalize about teens.

But like the rest of us, many aren’t getting enough fruits and vegetables.

In an article published at the National Institutes of Health website, researchers found three categories for teen behavior: unhealthful (26%), healthful (26%) and typical (47%).

The survey results showed the “typical youth” were least likely to exercise five or more days each week or to eat fruits and vegetables at least once a day.

The researchers found the “unhealthful” group consumed the most sweets, chips, french fries, and soft drinks. Youth in this group, the survey said, were more likely to report symptoms of depression and of poor physical health, such as backaches, stomachaches, headaches or feeling dizzy.

For the “healthful” group, about 65% of those students said they exercised five or more days per week — the highest rate of the three groups. The “healthful” students were least likely to spend time in front of a screen and were most likely to report eating fruits and vegetables at least once a day. Again, researchers found that teens in this group were least likely to consume sweets, soft drinks, chips and French fries. Finally, the “healthful” group reported the lowest rates of depressive symptoms and the highest life satisfaction ratings, according to the report.

To put the study in context, the Centers for Disease Control and Prevention recommends that high-school age girls eat at least one and a half cups of fruit and two and a half cups of vegetables a day, and high-school age boys consume at least two cups of fruit and three cups of vegetables a day. According to 2010 data, more than a quarter of students ate fruit once a day or not at all, while about a third of students ate vegetables once a day or not at all.

Teens like Katie Stagliano, 14, honored at last September’s Clinton Global Citizen Awards and a speaker at last year’s Midwest Produce Conference & Expo, can inspire both her peers and her elders.

Stagliano’s nonprofit organization starts and maintains vegetable gardens and donates the harvest to help feed people in need.

For all those radio ads to stop defiant teen behavior, with “parent-proven” programs, perhaps one of the best things we can do for our teens is to create an environment with ample encouragement and modeling for physical activity and fruit and vegetable consumption.

This is another reason why USDA efforts to improve nutrition for school meals and for food sold at schools is deserving our strongest support.

When communication breaks down about the inner world of our teens, at least we can talk fresh produce. When words fail about awkward topics, we can at least agree on the wonders of the honeycrisp apple and the white-flesh peach.

And that’s something.