Gettysburg Medical News
The Clinical View
 by P.E. Hoffsten, MD
4 January 2006

DOES FIBER REALLY MATTER?

Years ago, a missionary doctor working in the African Congo noticed that the natives had a very low incidence of appendicitis, diverticulosis, and cancer of the colon.  He hypothesized that this was because of their very high-fiber diet and thus the controversies began.

The first question to answer is, “What is fiber?”  Fiber can be defined as the undigestible portions of your food.  It primarily comes from plant sources of food such as fruits and vegetables.  It comes in two forms.  One of these is soluble fiber that primarily comes from fruits.  This type of fiber forms a gel in the intestine and facilitates the movement of food through the bowel.  When it arrives in the large bowel, bacteria there digest it and thus it plays no role in forming the bulk of a stool.  The other type of fiber is called insoluble fiber.  It is like that chewy, grass-like material that is left after you eat three or four sticks of celery.  It forms a major portion of the bulk of a stool.  It is very rich in vegetables and whole grains.

So what are the claims for the merits of eating fiber?  For some people, fiber does seem to be a comfort in providing regularity of bowel movements.  This is at least partially attested to by the number of products on the market such as Metamucil and Fiber Con.  These products are pure insoluble fiber.  They obligate a certain amount of water to remain in the stool, thereby keeping it soft and avoiding constipation.  For many people, this is a very real benefit and easily demonstrable.

A second claim made for fiber is that it will help lose weight and lower cholesterol.  At the very best, this is a shaky claim.  Try as I will, I have not found any controlled study showing that overweight individuals who start eating fiber lose weight.  It is true that high-fiber diets empty from the stomach slowly and the claim is made that this gives the individual a feeling of fullness and they don’t eat so much.  But I am not aware of any controlled study showing that eating high-fiber diets is associated with weight loss.

The next claim on the merits of fiber is that it decreases heart attacks and lowers cholesterol.  A review article in the February 2005 issue of the Archives of Internal Medicine analyzed the available information on the relationship between high-fiber diets and heart attack.  They concluded that indeed the high-fiber diet is associated with a lesser rate of heart attack.  However, I am not aware of any studies that have shown that a high-fiber diet lowers cholesterol in the blood.  This would be a very difficult study to undertake whereby a person has their blood cholesterol taken and the fiber in their diet measured.  Following this, the person would have to go on a measured high-fiber diet and then again measure the cholesterol.  I am not aware of any studies that have done this to show that the cholesterol actually does come down in people with high-fiber diets.

The last major claim for a high-fiber diet is that it prevents colon cancer.  An article published in the December 14, 2005 issue of the Journal of the American Medical Association clearly debunks this idea.  It is just not true.  The question was looked at from several angles.  One way was to measure the amount of fiber in individual’s diets and then watch to see if people developed cancer on either a high-fiber or low-fiber diet.  There was no difference in the studies done.  The second method of looking at this question was actually more interesting.  It is well known now that cancer of the colon comes from polyps.  If the person were to have a decreased incidence of colon cancer by taking a high-fiber diet, it would be predicted that the incidence of polyps in the colon would be less also.  It seems logical that the fewer polyps there are to form cancer, the fewer cancers there will be.  A study was done seeing if a high-fiber diet was associated with a decreased incidence of colon polyps.  The answer was that there wasn’t a hoot of difference between those on a high-fiber or a low-fiber diet.  Based upon all of the research available, at this time, it can be concluded that the fiber in a person’s diet has nothing to do with the incidence of colon cancer.

In a person’s lifetime, there is probably nothing that they will be more advised upon than what they should eat.  The number of diet books and the number of articles in our magazines that deal with dietary advice are everywhere.  You can receive advice on a high-protein low-carbohydrate diet or a low-protein vegetable diet.  If there is any advantage to a high-fiber diet, it probably comes more from what you do not eat rather than what you do eat.  A high-fiber diet has less meat and cheese and thus less high-cholesterol foods.  We already know that a diet low in cholesterol is one factor in preventing heart attacks and strokes.

But if one does have a perceived need for a high-fiber diet, how does one go about this?  Our food packaging in the grocery stores now has information regarding calories, salt, fats, carbohydrate, protein, but they don’t have anything in there about fiber.  Of course the most important source of fiber is vegetables, such as are on the vegetable rack, and they don't have any mark on them.  One way to get a high-fiber diet is to use the artificial products such as Metamucil or Fiber Con.  Another way is to employ a fourth of a cup of ground flaxseed with breakfast.  Remember this has the advantage of lots of omega-3 unsaturated fatty acids.  Foods that are rich in fiber are vegetables, whole grains, and fruits.  Foods low in fiber include meat, cheese, and dairy products.

The benefit of high fiber diets seem to come at those individuals who have 30 grams of fiber per day or more.  It is estimated that 73 percent of the US population has 20 grams or less.  The statistics clearly show that the more fiber in a person’s diet, the less likely they are to have a heart attack.  For this reason, it seems that fiber probably really does matter.