Overall, apples are a healthy food choice, rich in fiber and vitamin C. But sometimes you can have too much of a good thing. Apples are high in sugar and have also been known to cause gastrointestinal distress. Pesticide residues are another possible concern, as are allergic reactions in some people.
Most of the calories in apples come from sugar. A medium apple contains about 100 calories, and about 90 of those calories come from carbohydrates. The high fiber content of apples gives them a low glycemic index score, meaning that most diabetics will have few problems incorporating apples into their regular diet.
Most of the fiber in apples is soluble fiber in the form of pectin, although apple skins also contain a good amount of insoluble fiber. The high fiber content of apples can lead to gastrointestinal issues, including loose stools and sometimes diarrhea. Usually, this side effect occurs only if your body is unused to digesting a high-fiber diet and will disappear after your digestive system adjusts.
Some people report mild stomachache after eating apples. This is most likely another symptom caused by the high fiber content of apples. Digesting the fiber can cause gas to buildup in the gastrointestinal system, resulting in stomachache, cramps and flatulence. Again, this effect is usually transient.
If you do not purchase organic apples, you could be exposing yourself to trace amounts of pesticides. Peeling apples can eliminate much of the risk from residue. Much of the fiber and vitamin content of apples is found in the peel, however, so peeling apples will also reduce their nutritional value. Be careful, too, when scavenging windfall apples -- not only do you have no way of knowing the pesticides used on what you find, the fallen fruit may be contaminated with E. coli and can cause food poisoning.
Allergic reactions to apples are uncommon but not unheard of. Symptoms include itching around the lips and mouth, swelling of the lips and tongue, itchy and watery eyes and sneezing. If you're allergic to pears, you're probably also allergic to apples. Other associated allergies are birch pollen, raw potatoes, peaches and hazelnuts. Cooking the apples usually eliminates the problem.
One Myth: Cyanide
You may have heard that apple seeds are poisonous, but the risk of accidentally ingesting one is insignificant. While apple seeds do contain tiny amounts of cyanide, the amount is so small as to be essentially harmless.