•  not practicing good oral hygiene (a no-brainer, but often neglected);
• dried fruit and candy (high in sugar and sticks to the teeth);
• starchy foods (the starches in food can mix with an enzyme in your saliva and create an enamel-eroding acid);

  Also check out...

• fruit juices (whether sweetened or not, fruit juices are acidic and have lots of natural sugars);
• smoking;
• certain health conditions such as HIV and diabetes;
• pregnancy;
• drinking alcohol excessively; and
• lack of fluoride. 

Practicing Good Dental Hygiene 

If a healthy, white smile is one of your objectives, you will want to take other measures in addition to staying away from overly acidic drinks like diet soda. Practice the good dental hygiene practices recommended by the American Dental Association (ADA).