Excessive intake of dietary fiber may increase the risk of anemia

Many people may perceive the title of this article as strange. There's so much information on increasing the intake of fiber to improve health and body aesthetics. It is a fact that many people do not supply enough dietary fiber to their bodies, however, there are some individuals who eat too much of it. It mainly concerns physically active women on diet who are endangered with anemia much more than men. Why is it like this?

Fiber – what is it?

Fiber, also called dietary fiber, is a mixture of different compounds of vegetable origin, which do not decay under the influence of our digestive enzymes and are not absorbed from digestive tract. Nevertheless, their action on human body is positive and here are some examples:

  • influence on intestine bacteria,

  • influence on gastrointestinal motility,

  • slowing down the process of emptying stomach,

  • inhibition of the absorbtion of cholesterol,

  • attenuation of hunger,

  • lowering glycemia after a meal.

Kinds of fiber and recommended intake

There are different kinds of fiber that can be divided according to their qualities in the following way:

  • soluble in water (present in fruits pectines, gums and mucus often added to food products),

  • partly soluble in water (hemicellulose which can be found in cereals and bran),

  • insoluble (celulose found in fruits and vegetables, also lignin which can be found in cereal products).

There is no single theory on the suggested amount of fibre intake, however, majority of sources suggest the range between 20 to 40 g or 30 to 35 g. Higher doses are also sometimes suggested but it is not necessary in most of the cases.

Iron – physiological role and demand

Iron is an indispensable nutritional compound which has very important functions in human body. This element is a part of hemoglobin and myoglobin, thanks to which it conditions proper oxygenation of tissues and organs. Apart from that, iron is indispensable during the synthesis of many enzymes responsible for:

  • fatty acid metabolism,

  • prostaglandins bio synthesis,

  • some amino acids catabolism,

  • electrone transportation.

Suggested daily intake of iron is about 12 mg for men and much more – 18 mg for women. Additionally, people who train, demand more of this element. Insufficient intake of iron leads to anemia.

Iron can be found in many kinds of food, of both, vegetable and animal origin. The bioavailability of iron from vegetable-origin products is much less than from meat. The assimilation of this element is additionally lowered by:

  • phytates (present in cereal products),

  • oxalates (present e.g. in spinach),

  • calcium (present in diary products).

What has fiber to do with it?

The factors above are not fully comrehensive in the subject of iron absorption from digestive tract disruption. It occurs that the source of problems can be.. dietary fiber. Unfortunately, not many people seem to remember that, which is a pity, because people such as dietitians and trainers who suggest their client eating tons of bran, as well as people who eat products with a lot of fiber should pay attention to that. This dependency is not imaginary and it can be the source of serious problems. The proof for that can be found in the analysis made by dr Bushnell from the Codman Square Health Center, that showed that high intake of fiber is a factor which reduces the intake of iron from food.

It is worth to know that the problem may be not only the fiber itself (some of its fractions), but also phytic acid which accompanies it in the cereal products and is an anti nutrient joining iron creating insoluble complexes making the iron impossible to be absorbed. Therefore, not only supplements are the problem here, but also conventional food.


Of course, I didn't write this article to limit the consumption of fiber on purpose. I just wanted to pay attention to “the other side of the coin” which is to show that commonly recommended diet ingredient – fiber – has disadvantages if it's eaten in excess amount. No restraint in its consumption (or in eating food products rich in it) may lead to adverse consequences, especially for physically active women who are endangered with anemia.

Sources: Early Hum Dev 1987 Mar; 15 (2): 103-11. Nurse Pract 1992 Nov; 17 (11): 68, 71-4.