Gym members warm up on treadmills at Downsize Fitness in Addison, Texas. Membership at the gym is limited to people who have a high body mass index. LM Otero/AP hide caption

itoggle caption LM Otero/AP

Many Americans aren't getting the recommended seven to nine hours per night. Franck Camhi/iStockphoto.com hide caption

itoggle caption Franck Camhi/iStockphoto.com

It's not clear if diet soft drinks are the healthiest choice. ASSOCIATED PRESS hide caption

itoggle caption ASSOCIATED PRESS