Fiber bars contain a large dose of an essential nutrient, but they can also give you bloating, gas, cramping or, in the most severe cases, diarrhea. Fiber bars are most likely to produce such uncomfortable side effects if you eat too many of them too frequently before your body can get used to an increase of fiber in your diet.
Fiber provides bulk, assists with digestion and nutrient absorption, and can help you lose weight by making you feel full, and therefore eat less frequently or voraciously. It can also help your heart health by lowering your blood pressure and your overall cholesterol level, the latter by reducing the level of low-density lipoprotein, or "bad" cholesterol. Fiber can also help to alleviate hemorrhoids, irritable bowel syndrome, digestive tract inflammations known as diverticulitis and reduce your risk of type 2 diabetes, coronary heart disease and certain cancers, according to the American Academy of Family Physicians. One of fiber's major claims to fame is its ability to soften the stool which, in turn, can relieve constipation. Go overboard with the fiber, however, and the constipation relief can work all too well and result in diarrhea.
Fiber bars can contain from 9 g to 12 g of fiber per serving, which can take care of nearly half of your daily fiber requirement. The recommended daily dose of fiber is 25 g per day for women and 38 g per day for men up to age 50. Women and men over age 50 require at least 21 g and 30 g of fiber per day, respectively. If a 51-year-old woman ate two of the higher-fiber bars, she'd already be over her daily recommended limit, and that's not even taking into account other sources of fiber in her diet. Fruits, vegetables, beans, breads, cereals, grains and oatmeal all contain fiber.
Slow and Steady
The safest way to add more fiber to your diet is with a slow and steady approach. The American Academy of Family Physicians suggests increasing fiber with a single change, such as one lower-fiber fiber bar, then waiting up to a week to give your body time to adjust before increasing your fiber intake. Your body also requires plenty of water to properly digest fiber -- at least eight glasses of water daily.
If even a single fiber bar gives you uncomfortable side effects, perhaps try half a bar. Eating foods naturally rich in fiber is another approach; many high-fiber foods contain less fiber than a typical fiber bar. Prunes, for instance, contain 3.8 g fiber in a 0.5 cup serving. A 0.5 cup serving of beans generally yields between 6.2 and 9.5 g of fiber, with navy beans topping the list and great northern beans at the bottom. Other natural sources of fiber are sweet potatoes, with 4.8 g fiber for one medium potato; berries, with between 3.8 and 4 g fiber per 0.5 cup serving; and pears, with 4.4 g fiber in one small pear.