1. What are they and where do they come from?

Fiber is an indigestible substance that comes from the walls of plant cells. There are two types of fiber: soluble and insoluble [roughage]. The solubility of fiber refers to its ability to dissolve in water.

As the names indicate, soluble fibers dissolve in water, while insoluble fibers do not. Within the two categories of fiber there are several subcategories.

Dietary sources of fiber include: vegetables, fruits, grains, psyllium, oat bran, guar gum, and beans.

2. What does it do and what scientific studies give evidence to support this?

Fiber is best known for its ability to induce bowl movements. Although it has been used for thousands of years to treat constipation, fiber is known to enhance health in many ways. For example, insoluble fiber contributes to feelings of fullness.¹ Because fiber can not be digested, it acts as dietary "filler." When consumed, fiber occupies space in the stomach, and upon absorbing water and macronutrients, expands in volume. Resulting from the consumption of insoluble dietary fiber, individuals may experience fullness [satiety], a decrease in overall caloric intake, and possible weight loss.^{2, 3}

Soluble fiber has been shown to reduce the speed of gastric emptying. The slowing of gastric emptying will result in prolonged feelings of fullness. This, theoretically, will result in an overall reduction of consumed calories, thus contributing to weight loss. Therefore, if weight loss is your goal, it is important that fiber be consumed, regardless of type.

Research has shown that soluble fiber leads to an overall reduction in bad cholesterol levels.⁴ For this reason, it can also reduce the risk of coronary heart disease.^{5, 6}

The consumption of pectin [found in many fruits] is known to lower blood sugar levels. This would potentate the function of insulin in the body. Increased fiber intake [specifically pectin and mucilage] has been correlated with lower occurrences of diabetes in the general population. Fiber [pectin] also help reduce the occurrence of gall stones.

Although it is commonly believed that fiber reduces the risk of developing colon cancer, the literature on this subject is not conclusive.. It has not yet been fully established what role, if any, that fiber plays in protecting the colon. One study, however, indicated that consuming fiber offered protective benefits from the occurrence of breast cancer.⁷

3. Who needs it and what are some symptoms of deficiency?

Everyone should consume a minimum amount of fiber daily. Populations that may benefit most from the consumption of fiber include: diabetics, the overweight or obese, and athletes.

Research has shown that soluble fiber has the ability to lower blood sugar levels in diabetics by raising insulin levels. This means, for the insulin dependant, that consuming fiber would, theoretically, decrease the need for the introduction of insulin from an external source.⁸

For the overweight or obese, the inclusion of fiber, especially when eating meals high in saturated fats, may contribute to weight loss in two ways. The first way has to do with the ability of fiber to expand in the stomach, thus speeding the onset of satiety, and thus a decrease in the caloric mass of food eaten. The second way has to do with fibers ability to absorb macronutrients. When fiber absorbs fat molecules, the fat molecules are unable to be metabolized and thus pass through the body. This means, simply, that they fail to be stored as body fat.

For athletes, the inclusion of dietary fiber into a nutritional program may prove beneficial when dieting down and attempting to reduce body fat, and when attempting to increase insulin levels naturally, without having to resort to the consumption of simple or refined carbohydrates. Consumption of simple carbohydrates may lead to fat storage; consumption of fiber will not. What's more, the use of fiber, and specifically pectin, will slow the rate at which consumed carbohydrates are released into the bloodstream. This will result in avoiding unnecessary insulin spikes that encourage the storage of body fat.

When on a high protein diet, constipation is a possibility, and so is intestinal inflammation. Individuals suffering from constipation may benefit from the consumption of insoluble fiber,9 and research has also demonstrated that intestinal inflammations occur less frequently in those who consume adequate levels of dietary fiber.¹⁰

4. How much should be taken? Are there any side effects?

25 to 30 grams for adults is recommended daily.¹¹ Consuming too much fiber can result in the body being unable to absorb some vitamins and minerals.¹² For this reason, when consuming large amounts of fiber, it is important to increase protein intake, as high fiber intake may also block the absorption of macronutrients.

Diabetics and individuals suffering from sclerosis should consult with a qualified physician prior to use.

REFERENCES

1. Burley VJ, Blundell JE. Action of fiber on the satiety cascade. In Kritchevsky D, Bonfield C, Anderson JW, eds. Dietary fiber: Chemistry, physiology, and health effects. Plenum Press, New York. 1990;227-46.
2. Hylander B, Rossner S. Effects of fibre intake before meals on weight loss and hunger in a weight reducing club. Acta Med Scand 1983;213:217-20.
3. Rossner S, Von Zweigbergk D, Ohlin A, Ryttig KR. Weight reduction with fibre supplements. Results in two double-blind studies. Acta Med Scand 1987;222:83-8.
4. Todd PA, Befield P, Goa KL. Guar gum: a review of its pharmacological properties and use as a dietary adjunct in hypercholesterolemia. Drugs 1990;39:917-28.
5. Wolk A, Manson JE, Stampfer MJ, et al. Long-term intake of dietary fiber and decreased risk of coronary hart disease among women. JAMA 1999;281:1998-2004.
6. Jenkins DJA, Kendall CWC, Ransom TPP. Dietary fiber, the evolution of the human diet and coronary heart disease. Nutr Res 1998;18:633-52 [review].
7. Adlercreutz H, Fotsis T, Hekkinen R, et al. Excretion of the lignans enterolactone and enterodiol and of equol in omnivorous and vegetarian postmenopausal women and in women with breast cancer. Lancet 1982;2:1295-9.
8. Anderson JW, Gustafson NS, Bryart CA. Tietyen-Clark J. Dietary fiber and diabetes. J Am Diet Assoc 1987;87:1189-97.
9. Kritchevsky D. Protective role of wheat bran fiber: preclinical data. Am J Med 1999;106(1A):28S-31S.
10. Aldoori WH, Giovannucci EL, Rockett HR, Sampson L, Rimm EB, Willett WC.A prospective study of dietary fiber types and symptomatic diverticular disease in men. J Nutr. 1998 Apr;128(4):714-9.
11. ADA Reports. Position of The American Dietetic Association: Health implications of dietary fiber - technical support paper. J Am Diet Assoc 88:217-221, 1988.
12. ADA Reports. Position of The American Dietetic Association: Health implications of dietary fiber. J Am Diet Assoc 88:216, 1988.