In nutrition circles, one often hears "eat fiber, it's good for you". But fiber is a carbohydrate and those are supposed to be bad, or at least severely limited. What gives?
The resolution to this dilemma lies in examining more closely just what fiber is and what it does for you.
What Is Fiber?
Fiber is, it's true, a type of carbohydrate. That is, fiber compounds are composed of molecules whose chief elements are carbon, hydrogen and oxygen in combination. But there is a key difference between fiber and other types of carbohydrate: it doesn't break down during digestion.
Both simple sugars (simple carbs) and starches (complex carbs) are broken down by digestive enzymes, releasing energy the body uses for an infinite variety of vital processes. Fiber is not, at least not much. That simple difference leads to a number of beneficial effects.
Why Is Fiber Good?
Insoluble fiber, by definition, does not dissolve in water. As such, it moves through the digestive system where it helps increase the bulk of stools. That helps prevent constipation. It also moves through the intestines relatively fast, which generates signals to the brain that you're full. In that way, it discourages overeating and the accompanying excess consumption of calories.
Insoluble fiber is contained in whole-wheat flour and wheat bran, many types of nut and several vegetables that contribute 'roughage' to the diet.
Soluble fiber, by contrast, does dissolve in water and so forms a type of gel that makes its way through the digestive system. As a result it helps regulate blood glucose levels. On route it helps cleanse the tract of bacteria.
Soluble fiber is part of a wide variety of foods, including oats and barley, carrots and peas, apples and citrus fruit, and beans.
A high fiber diet helps decrease the odds of heart disease by lowering LDL cholesterol (the undesirable type).
It slows the absorption of sugar contained in food consumed, which helps smooth out any spikes. That helps improve a number called the Glycemic Index, one key to a healthy diet according to some diet programs such as the South Beach Diet.
Controlling blood glucose levels has another beneficial effect, according to many studies. Insulin levels are related to blood glucose levels. Excess glucose over long periods increases the odds of acquiring Type 2 diabetes. A high fiber diet can help decrease those odds.
Since fiber is not broken down, it adds bulk without calories. That contributes to a feeling of fullness and satiation without the accompanying potential for storing excess calories as fat. Thus, it contributes mightily to any weight loss program.
How Much Daily Fiber Is Good?
There is no official RDA (Recommended Daily Allowance) for fiber as there is for many other nutritional components. But official sources put the desirable amount at roughly 25 grams per day. The average consumption is often much lower, around 15 grams per day.
One study of over 500 subjects conducted at the University of Massachusetts Medical School over one year showed that those who consumed 22 grams or more were 63% less likely to have high CRP levels. High CRP (C-reactive protein) is linked with higher risk of heart disease and diabetes.
Summary
Like any aspect of diet and nutrition, the value of fiber can be (and sometimes is) overstated. But numerous studies agree that a high fiber diet has definite benefits. As with any proposed change in diet, consulting your physician first is wise.
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