What foods destroy tooth enamel?

Since tooth enamel is almost 100 percent mineral, anything that can de-mineralize enamel is bad. That would be acids, like lemons or orange juice or a diet that’s high in proteins, which basically ignites acids already existing in the mouth.

Foods and drinks that contain sugar will feed the acid-producing bacteria that cause cavities. Research has shown that for every time sugar is consumed these bacteria produce acid for about 20 minutes continuously. This acid will destroy the enamel if the saliva in your mouth does not have enough time to neutralize it. So, if you are sipping a sugar containing drink throughout the day or for a few hours then you are constantly feeding these acid producing bacteria and you have a greater chance of getting cavities. It is best to drink your drink in one sitting then to sip it throughout the day. Or if you are snacking throughout the day, popping things like cookies or donuts or potato chips in your mouth you will be at a higher risk for getting cavities. So, keep snacking to a minimum to reduce your risk of getting cavities.    

Foods that are acidic in nature like lemons and any carbonated beverages like soda, seltzer etc. should also be taken with caution as they can potentially have an erosive effect on tooth enamel. That doesn't mean that you should not have lemons in your diet. It just means you should not be sucking on them regularly or constantly sipping water with lemon in it or soda for long periods of time.
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Regular soda is both highly acidic and high in sugar content and is a deadly combination that can damage teeth in both ways. Minimize the amount of soda you drink and drink it with a straw so that most of it goes down rather than on your teeth. Diet soda may not have the sugar in it but it is still highly acidic and harmful to teeth. 

All food will eventually destroy tooth enamel. Well, the food itself generally won't, but the bacteria and plaque that leftover food particles cause will. This is why it is important to brush and floss your teeth -- this cleans away food particles, and helps keep your teeth intact.

That said, some foods produce more bacteria faster -- sugar is a culprit here, as are acidic drinks (like cola and other soda/pop). This is why us dentists say to avoid these if you can. Drink more water, and less soda. It's a lot better for you (and will help wash away food particles as well!)