What not to eat?
From time immemorial candy and chocolates have been linked to decaying teeth. It isn't the candy or the chocolate that's at fault, it's the excessive sugar and their sticky nature that is the problem. If their remnants are not rinsed or cleaned immediately, they can lead to decay. Similarly, excessive caffeine (in tea, coffee, aerated beverages, etc) can cause stains on teeth in the long run. Excessive starch is harmful as well, as one of the by-products saliva breaks it down into sugars which can cause the enamel to erode. Similarly, citrus fruits when had in excess cause erosion of the enamel.
Like everything in life, too much of anything can be bad. It is not humanly possible to avoid all things that are unhealthy. What we can do is, rinse our mouth whenever we eat/drink something and consume everything in limited amounts. Another thing you can do is, make a conscious effort to consume foods and drinks which are healthy for teeth, oral health and general health.
Some healthy food options
1) Water: Drink plenty of water. It rinses the mouth naturally and prevents excessive food build-up in the mouth. Also, water is the main component of saliva, and drinking lots of water, replenishes and improves saliva quality. Saliva is the mouth's first line of defense against plaque and infection.
2) Green tea: It is rich in antioxidants and compounds called polyphenols. Green tea helps provide relief from inflammation (swelling) in gums dues to its anti-oxidant properties and in the long run reduces chances of gum infection. Polyphenols cause suppression of plaque forming bacteria and thus prevent the production of harmful acids by them.
3) Foods rich in vitamins and minerals: Nuts (such as peanuts, almonds, walnuts), green leafy vegetables, eggs, etc help keep teeth strong and healthy. They provide us with a wide range of vitamins, calcium, phosphorous and other minerals, thus helping in deposition of minerals on teeth which have eroded (demineralized) Vitamin D and Calcium also help to keep the bones strong.
4) Fruits and Vegetables rich in Fibre: These are foods which often require a lot of chewing. When you chewing high fiber foods, they stimulate flow of saliva. Also, they have a high water content because of which they are self cleansing foods, and don't stick to teeth. With increased saliva and water from the food itself, the effect of acids and sugars of food is neutralized. Chewing also displaces plaque and thus prevents bacterial build up and growth.
5) Dairy products: Milk, cheese, yogurt, etc are rich in calcium, phosphates and Vitamin D. Thus, they help in keeping teeth and (jaw) bones strong and healthy. They also partially remineralize teeth which have eroded. Milk has a neutralizing effect on the acid produced by bacteria in plaque, thus preventing damage.
So, chose what you eat and how much you eat wisely. These 5 choices above are healthy for your teeth and body.