Herb Drug Mix: Effects of Fibers, Tannins and Phytates

The absorption mystery

| March/April 2001


Flaxseeds are rich in fiber, so they may reduce the absorption of certain drugs.

Joe Coca

Have you ever stopped in the middle of a meal and thought about what you’re putting into your body? If you were to perform a nutritional analysis of all of the different carbohydrates, proteins, fats, vitamins, minerals, and other chemicals contained in the food you’re eating, you might find yourself wondering how it would ever be possible to digest and assimilate such a complex mixture. Somehow, we’re able to take in an astounding variety of foods, grind them up, blend them together into a slurry, add in some enzymes, and extract from them the nutrients we need to stay healthy.

It’s precisely this background information that comes to mind when a patient asks me whether it’s safe to take more than one herb, vitamin, or mineral supplement at a time and whether any herbs or supplements could potentially interfere with prescription medications.

On one hand, the possibilities for a potential interaction are enormous—entire chapters of nutritional textbooks are devoted to the subject. And more recently, medical journals are also addressing the subject of herb-drug interactions in some detail. It’s impossible to read such texts and not end up paranoid about what could go wrong. On the other hand, our digestive tracts are used to dealing with a high level of complexity. The nutrients that we ingest are always interacting with each other. This interaction may be synergistic, neutral, or antagonistic. Consequently, the only thing that’s important is the result—is it beneficial or not?

A potential for interference

Adding an herb or vitamin supplement to the mix is not that different from adding a food. It’s difficult to predict what the outcome might be based on analyzing the potential interactions of individual constituents. Again, there’s only one significant question: What is the final result?

One area of potential interaction that’s particularly complex has to do with so-called “non-nutrient” substances in foods and herbs that could potentially interfere with absorption of nutrients or medications. These substances act by either binding to the nutrient or by making it precipitate (so that it’s no longer dissolved in the slurry and therefore unable to be absorbed). When this happens, some or all of the nutrient or medication gets excreted without making it into the bloodstream. There are three important groups of these non-nutrient substances: fibers, tannins, and phytates (or phytic acid).

Fibers include gums, resins, and mucilages. They are abundant in certain seeds such as flax (Linum usitatissimum), fenugreek (Trigonella foenum-graecum), and psyllium (Plantago spp.). Oat and barley bran are also good sources. So are konjac root (Armophophallus konjac) and guar gum (Cyamopsis tetragonolobus). Marsh-mallow root (Althaea officinalis) and slippery elm bark (Ulmus rubra) are well known for their mucilages.

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