Apple pectin, a soluble fiber found in apples, also is found in other fruits. However, the pectin content of apples is particularly high compared with other fruits. Apple pectin is available as a dietary supplement and commonly used for purported digestive benefits. You're unlikely to feel side effects from the pectin content of one apple. Taking apple pectin supplements -- a concentrated form of pectin -- can cause side effects. Talk to your doctor before taking apple pectin supplements.
Common apple pectin side effects include bloating and gas. Diarrhea is less common, but does occur. Because apple pectin is fiber rich, it absorbs several times its weight in water. This means it expands in your stomach by drawing water from the intestines. The beneficial side effect of this is a slightly reduced appetite. The side effects of apple pectin are the same as other high-fiber foods. You're more likely to experience side effects if you abruptly introduce high-fiber foods when your body is accustomed to a lower fiber diet. Gradually increase your fiber intake to reduce the risk for side effects.