The characters Gamora (Zoe Saldana) in "Guardians of the Galaxy" and Black Widow (Scarlett Johansson) in "Avengers: Age of Ultron" are female superheroes who, we'd guess, are fueled by a potassium-rich diet. They’ve got to be, to keep their cool and have such grace and strength.

Potassium definitely is a superhero among nutrients. It builds muscle strength. That, in turn, builds stronger bones.

A study in the journal “Bone” shows that a 10 percent boost in muscle strength in kids just 6 years old can postpone osteoporosis decades later by up to 13 years.

Another study in “JAMA Pediatrics” found that young girls who get the most potassium (2,400 mg a day or more) are far more likely to have healthy blood pressure as they get older.

Making sure potassium levels are healthy may even help prevent diabetes.

The recommended intake for girls 9 and older is between 4,300 and 4,500 mg daily. But few get that much, because 40 percent of the average North American teen's diet is filled with empty calories from soda, fruit drinks, dairy desserts, pizza, and solid fats.

So if you want your girls to grow up to be superwomen, make sure they get plenty of potassium-rich foods.

The top 10 sources are: beet greens, Swiss chard, spinach, bok choy, beets, Brussels sprouts, broccoli, cantaloupe, tomatoes, and asparagus. Other good sources include raspberries, strawberries, and watermelon.

There's got to be some items on that list your kid likes! And a smoothie is always a great way to blend some super-nutrients into a teen's diet.