How a Food and Drug Interaction Happens

When you eat, food moves from your mouth to your stomach to your small intestine, where the nutrients that keep you strong and healthy are absorbed into your bloodstream and distributed throughout your body. Take medicine by mouth, and it follows pretty much the same path from your mouth to your stomach, where it's dissolved and passed along to the small intestine for absorption. Nothing is unusual about that.

The problem, however, arises when a food or drug brings the process to a screeching halt by behaving in a way that stops your body from using either the drug or the food (see Figure 25-1). Many possibilities exist:

Some drugs or foods change the natural acidity of your digestive tract so that you absorb nutrients less efficiently. For example, your body absorbs iron best when your stomach is acidic. Taking antacids reduces stomach acidity — and iron absorption.

1 Some drugs or foods change the rate at which food moves through your digestive tract, which means that you absorb more (or less) of a particular nutrient or drug. For example, eating prunes (a laxative food) or taking a laxative drug speeds things up so that foods (and drugs) move more quickly through your body and you have less time to absorb medicine or nutrients.

1 Some drugs and nutrients bond (link up with each other) to form insoluble compounds that your body can't break apart. As a result, you get less of the drug and less of the nutrient. The best-known example: Calcium (in dairy foods) bonds to the antibiotic tetracycline so that both zip right out of your body.

1 Some drugs and nutrients have similar chemical structures. Taking them at the same time fools your body into absorbing or using the nutrient rather than the drug. One good example is warfarin (a drug that keeps blood from clotting) and vitamin K (a nutrient that makes blood clot). Eating lots of vitamin K-rich leafy greens counteracts the intended effect of taking warfarin.

1 Some foods contain chemicals that either lessen or intensify the natural side effects of certain drugs. For example, the caffeine in coffee, tea, and cola drinks reduces the sedative effects of antihistamines and some anti-depressant drugs but increases the nervousness, insomnia, and shakiness common with some diet pills and cold medications containing caffeine or a decongestant (an ingredient that temporarily clears a stuffy nose).

Figure 25-1:

Some foods may affect the way your body interacts with drugs.

Figure 25-1:

Some foods may affect the way your body interacts with drugs.

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