In the movie "Batman v Superman," Henry Cavill plays the Man of Steel. But the super-fit actor wasn't always in good shape. He said that in boarding school, "They used to call me Fat Cavill. I actually had rolls of fat on me." 

He's lucky he was able to shed that excess weight. A new study in the journal JAMA Pediatrics points out that most adolescents with obesity carry it into adulthood, and are then at increased risk for insulin resistance, impaired glucose tolerance, elevated bad cholesterol, and high blood pressure, as well as some cancers.

And another recent study found that men with obesity in their late teens are twice as likely to have a blood clot in their lungs or legs as they get older. 

Unfortunately, these days 20% of boys ages 12 to 19 in the U.S. are obese.

So what's the most effective way to help your teenage son achieve a healthier weight? The JAMA study found it takes a combined approach:

• Family involvement is key to supporting and sustaining weight loss. That means Mom and Dad working at it too.

• Results are enhanced if you work with a registered dietitian, exercise physiologist, and psychologist who can support and direct your child's efforts.

• Establish a diet plan your child can follow. The Traffic Light Diet lists go-foods, caution-foods, and no-go-foods. Search for "What should I eat often when following the Traffic Light eating style?" and "What should I eat rarely when following the Traffic Light eating style?"