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The Effects of Excess Fiber on Vitamin Absorption

Getting the recommended 21 grams to 38 grams per day of fiber in your diet may help lower your risk for constipation, high cholesterol, Type 2 diabetes, heart disease and stroke, according to University of Maryland Medical Center. Consuming more than 50 grams per day of fiber, however, may interfere with the absorption of certain nutrients.

  1. Vitamins From Food

    • Eating a diet containing the recommended amount of fiber didn't result in decreased amounts of vitamins and minerals in the blood in a study published in "Public Health Nutrition" in June 2004. The study accounted for the higher micronutrient amounts found in the high-fiber foods, but was conducted with healthy middle-aged women and the results might not be the same in people who are more vulnerable to micronutrient deficiencies.

    Vitamins From Supplements

    • People given test meals fortified with vitamins B-12 and E and a type of fiber called konjak mannan absorbed less vitamin E but the same amount of vitamin B-12 as when they were given these meals without the additional fiber in a study published in "The Tohoku Journal of Experimental Medicine" in 2008. The study authors note that the fiber may affect absorption of fat-soluble vitamins more than water-soluble vitamins. Another study, published in the Russian journal "Voprosy Pitaniia" in 2010, found that supplementing with fibers, including lignan, microcrystalline cellulose and wheat bran, could decrease the absorption of vitamins including thiamine, riboflavin and vitamins A, C and E.

    Other Nutrients

    • Excessive dietary fiber intake may also have an adverse effect on the absorption of some minerals, including calcium, iron, magnesium and zinc, according to University of Arizona Extension. This is because fiber can cause your food to pass through your digestive tract more quickly, leaving less time for these minerals to be absorbed.

    Significance of Effects

    • While consuming purified fiber, such as that from supplements, may interfere somewhat with vitamin and mineral absorption, the World Health Organization notes that people who get the recommended amounts of nutrients while following a high-fiber diet aren't likely to experience vitamin or mineral deficiencies. Foods high in fiber also tend to be high in vitamins, so there isn't much risk for vitamin deficiencies as long as you get your fiber from foods instead of supplements.

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