Fiber - The ins and outs

The results of a study in teenagers were recently reported in the American Journal of Clinical Nutrition: Over the two-year study period, about half of the participants had decreased their consumption of fiber by an average of about 6 grams per day, while the remainder increased their fiber intake by a similar amount. The investigators were looking at belly fat, which is the most dangerous type of fat; fatter waistlines increase the risk of diabetes and heart disease. Belly fat increased 21 percent for the study participants who were eating less fiber, but the adolescents who upped their fiber intake had a 4 percent reduction in belly fat.

Separately, it was earlier reported at the University of Leeds that pre-menopausal women who eat 30 grams or more of fiber a day cut their risk of breast cancer by 52 percent. This study involved nearly 36,000 women and lasted over eight years. I found these conclusions outstanding! So what's going on with fiber and our health? Exactly what is fiber anyway? What are the best sources of fiber and what are its health benefits?

Officially, fiber is a type of carbohydrate that the body can't digest. Great sources are whole fruits and vegetables, whole grain breads and breakfast cereals, and all manner of beans. The daily amount of fiber that is currently recommended depends on the number of calories that you consume each day. Most adult women should shoot for over 20 grams of fiber a day; teens and men should aim for over 30 grams.

Before discussing fiber's health benefits, let's first bust two myths:

1. All fiber is created equal. Not true. There are two basic types of fiber, with different functions. Insoluble fiber is found in wheat bran, nuts and many vegetables. Its structure is thick and rough, and it won't dissolve in water, so it zips through your digestive tract. Conversely, soluble fiber is found in oats, beans, barley and some fruits. It dissolves in water to form a gel-like material in your digestive tract. This allows it to slow the absorption of sugar into your bloodstream.

2. Fiber has no calories. Not true. Your small intestine can't break down soluble or insoluble fiber; both types just go right through you. That's why some experts say fiber doesn't provide any calories. However, this claim isn't entirely accurate. In your large intestine, soluble fiber's molecules are converted to short-chain fatty acids, which do provide four calories per gram, as with all carbohydrates. (Insoluble fiber has essentially zero calories.)

Finally, let's review a short list of fiber's health benefits and discuss the reasons for these benefits.

• Avoiding and relieving constipation. Fiber can absorb large amounts of water in the bowels, and this makes stools softer and easier to pass.
• Heart disease. Foods containing soluble fiber can have a positive influence on cholesterol, triglycerides, and other particles in the blood that affect the development of heart disease.
• Gallstones and kidney stones. Rapid digestion leads to a rapid release of glucose (sugar) into the bloodstream. To cope with this, the body has to release large amounts of insulin into the bloodstream, and this can make a person more likely to develop gallstones and kidney stones (in addition to diabetes and high cholesterol).
• Keeping Weight Under Control. Foods containing plenty of fiber have more bulk than low-fiber foods. Therefore, fiber can sometimes slow the onset of hunger because the contents of the stomach are bulkier and are retained longer. Here's a tip: avoid foods that have been made easier to eat by the removal of fiber, such as fruit juices. You would be far better off to eat an apple and then drink a glass of water, rather than having a glass of apple juice (which contains no fiber).

Indeed, the list of the health benefits of dietary fiber is much longer. It is safe to conclude that paying more attention to fiber may go a long way to improving your health and avoiding disease.