Physical activity helps control weight by using excess calories that otherwise would be stored as fat. According to the Weight Control Information Network (WIN), a national information service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health (NIH), studies show that physical activity can also help improve mood and self image and may reduce depression and stress. Here are some tips to give to teens:

• After school is a perfect time to enjoy some physical activity. "Make a date" with a friend to walk or bike to counter the afternoon energy slump.
• To become more active throughout the day, take advantage of any opportunity to get up and move around. Take a short walk around the block; walk up the stairs instead of taking the elevator; or walk or ride a bike to school instead of taking the bus. If you take care of younger siblings or other children after school, don't just watch them play tag or kick a ball around—join them!
• What might appear to be "chores" can also get your heart pumping. Weeding the garden, walking the dog, mowing the lawn and even vacuuming are all physical activities. Offer your services to your neighbors and it may also be a chance to earn some extra spending money.
• Choose activities you enjoy that fit your personality and schedule. For example, if you like team sports or group activities, join a community sports team or take an aerobics or other exercise class. If you prefer individual activities, choose swimming, jogging or walking. Plan activities for the time of day when you have more energy so it won't seem like a chore to get active. Better yet, team up with a friend so you motivate each other.

"The after-school period is a really critical time for teens because they're usually famished and looking for a quick snack—a combination that can sometimes lead to less-than-ideal dietary choices," said Jo Ann Hattner, M.P.H., R.D., a clinical nutritionist at Stanford University Medical Center. She recommends making snacks quick and portable to help improve food choices for busy teens. Below are tips to help quell teens' hunger until dinnertime:

• Make after-school snacks into mini-meals. Quick choices might include a sandwich, a quesadilla or wrap, or last night's leftovers.
• Shakes made in the blender from frozen fruit, yogurt and juice are quick and portable. Also, juice bars are popular around the country. They offer made-to-order fruit and vegetable juice drinks that can provide an afternoon snack option.
• Have a good selection of nutritious snack foods on hand so teens can easily help themselves to something tasty and satisfying. Good options might include sliced cheese and crackers, cut vegetables with a low-fat dip or salsa or, a bowl of cereal with milk and fruit.

According to the CDC, 29 percent of students eat the recommended five or more servings of fruits and vegetables daily.