ADA position papers can be found on the American Academy of Nutrition and Dietetics website.  The position papers are published in the Journal of the Academy of Nutrition and Dietetics, and should be cited as online journal articles.

To cite it you can use Noodle Tools and select journal article. 

To create a Noodle Tools account

click the REGISTER button on the trial login page:
https://my.noodletools.com/logon/signin?group=29316&code=6355

After clicking REGISTER, the user will be prompted for the trial username/password:
Username: trial14513
Password: wuwi2jama