Acidic foods have a potential hydrogen, or pH, score of 6.9 or below. After you eat them, your stomach releases hydrochloric acid -- an ultra-acidic substance necessary for their digestion. Contrary to popular belief, acidic foods do not directly raise the acidity of your blood, stomach or entire body, according to Health Services at Columbia University in New York. Although many acidic foods are nutritious, they cause problems for some people.

In general, fruits are the most acidic foods. Particularly acidic varieties, such as citrus fruits, tomatoes, blueberries, grapes and apricots, are also top sources of antioxidants. Citrus fruits, blueberries and tomatoes provide rich amounts of the antioxidant vitamin C, which plays an important role in your immune system, wound healing and collagen production. Beta-carotene, which is an A-vitamin present in apricots, helps to regulate your immune system and promotes healthy surface linings of your eyes and respiratory, digestive and urinary tracts. Tomatoes and tomato products are prime sources of lycopene -- an antioxidant associated with a reduced risk for heart disease and prostate cancer, according to the Linus Pauling Institute.

Whole grains, fruits and vegetables are top sources of fiber -- an indigestible form of carbohydrate that promotes digestive function, appetite control and positive cholesterol levels. Although not as low-ranking in pH as fruits, whole grain foods, such as brown rice, wild rice, whole wheat bread and wheat-based cereals, are acidic. Most vegetables, including spinach, carrots, cabbage, beans and squash, are also moderately acidic.

Gastro-esophageal reflux disease is a chronic condition characterized by frequent acid reflux, which happens when stomach contents move back up into your esophagus after eating. If you have GERD, your doctor may suggest avoiding acidic foods, according to Columbia University. When highly acidic foods are among your stomach contents, they may increase the burning sensation associated with reflux when they come into contact with your esophagus.If you are prone to acid reflux, limit particularly acidic foods and beverages, such as tomato sauce, orange juice and coffee, and replace acidic fruits in your diet with lower-acid varieties, such as bananas, papaya and melon.

Another downside of acidic foods involves your teeth. Acidic fruits, juices and soft drinks contain natural acids that can wear away at tooth enamel. As this protective outer layer erodes, the inner parts of your teeth become exposed, increasing your risk for pain and sensitivity. If your teeth are sensitive to acidic foods, the British Dental Association recommends limiting acidic foods to meals only, avoiding regular and diet soft drinks and ending your meals with milk or cheese, which helps neutralize the acid.