By Kimberly Beauchamp, ND
Healthnotes Newswire (November 10, 2005)—Consuming the recommended daily amount of fiber may lead to iron deficiency in young women, reports the European Journal of Nutrition (2005;44:334–40).
Fiber is the indigestible portion of carbohydrate found in plant foods. Soluble fiber, which dissolves in water, is found in oats, legumes (peas, beans, and lentils), apples, berries, citrus fruits, barley, carrots, and pears. Insoluble fiber, which does not dissolve in water, is found primarily in whole grains, wheat bran, and vegetables. Both types are important components of a healthy diet. Soluble fiber helps to lower cholesterol levels, while insoluble fiber adds bulk to the stool, preventing constipation. High-fiber diets are associated with a lower risk of heart disease, diabetes, diverticular disease, and obesity. Because of this, it is recommended that adults eat between 20 and 35 grams of fiber each day. The appropriate grams of daily fiber for children two years old and older can be calculated by adding five to their age in years. For example, an eight-year-old should get 13 grams of dietary fiber each day.
While whole grains are richer in fiber than refined grains, they also contain a compound called phytate, which interferes with the iron absorption. Because iron is necessary for proper oxygenation of the blood, people who suffer from iron deficiency have less oxygen available to their body and may complain of shortness of breath and fatigue. Women of childbearing age are more likely than other groups to suffer from iron deficiency because of their menstrual blood loss.
Two types of iron are available from foods: heme and non-heme iron. Heme iron, found in liver, oysters, shellfish, and meats, is much more absorbable than the non-heme iron found in beans, dried fruits, blackstrap molasses, and dark green leafy vegetables.
Because of the potential for some fiber-rich foods to interfere with iron absorption, the new study investigated the effect of a high-fiber diet on the iron status of 41 women (average age 25 years). The women were given 300 grams of a fiber-rich wheat bread with or without phytase, an enzyme that breaks down phytate, every day for four months. The bread provided the upper amount of recommended daily fiber. At the beginning of the study and after two and four months, the women’s blood was tested for ferritin (a measure of the iron stores in the body) and hemoglobin (the oxygen-carrying protein in the blood).
The phytate content of the bread decreased significantly with the addition of phytase; however, the addition of phytase did not appear to affect iron status among the women in the study. In both groups, ferritin levels decreased significantly by 27% after two months, and remained stable thereafter. Hemoglobin levels decreased significantly after four months. These findings suggest that as the iron stores were being depleted, the oxygen-carrying capacity of the blood eventually began to drop, as indicated by decreasing hemoglobin levels.
How, then, can people get enough fiber without compromising iron absorption? Whole grains are just one source of fiber; eating an assortment of fruits, vegetables, and legumes may help meet the requirements for dietary fiber intake without interfering with iron absorption to the extent that whole grains do. Supplementing with vitamin C will also boost iron absorption, and cooking in cast iron pans can add iron to the foods prepared in them. Eating meat, poultry, and fish also helps increase the absorption of the iron in different foods. The use of stomach acid-lowering medications (calcium carbonate [TUMS]; lansoprazole [Prevacid]; esomeprazole magnesium [Nexium]) hinders the absorption of iron and other minerals and should only be used as necessary.
Kimberly Beauchamp, ND, earned her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She cofounded South County Naturopaths in Wakefield, RI. Dr. Beauchamp practices as a birth doula and lectures on topics including whole-foods nutrition, detoxification, and women’s health.
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