Everyone knows it: Eating well is almost universally the first-line defense for both managing and treating many diseases. But not everyone realizes that food’s “medicinal” properties can also influence medicines in the body—enough that people should consider what they eat and drink while taking medication.
Delicious, nutritious…and therapeutic
Some foods are packed with disease-fighting nutrients that have been shown to help with particular conditions. For example:
Grapefruit is a rich source of vitamin C and flavonoids, and may even help lower high cholesterol levels.
Pomegranate has been shown to slow atherosclerosis progression.
Dark-green leafy vegetables are loaded with lutein (for healthy eyes), magnesium (for a strong heart and reducing negative effects of stress), and fiber (for healthy digestion).
While these tasty, wholesome foods have these proven benefits and more, each is also known to interact with certain prescription medications—some with potentially serious consequences.
What we eat affects body chemistry
Eating to support health makes food a kind of medicine—and viewing it as that is a helpful reminder that what we eat creates chemical reactions in the body. So adding more chemical reactions—such as supplements and drugs—to the mix should be done with some consideration. The types of interactions that food may have with medicines include:
Beneficial: Replenishes depleted nutrients: Eating more of a nutrient-rich food may help replenish nutrients when a medication obstructs or depletes it from the body.
Beneficial: Side effect prevention: Eating more of a nutrient-rich food may help prevent or reduce the likelihood or severity of a potential side effect caused by a medication. Taking certain medications on an empty stomach can sometimes cause side effects such as nausea, solved by taking the medication with a meal.
Beneficial: Positive interaction: Some medications are more easily absorbed when taken with food, improving their action in the body. Some, for example, are fat-soluble, and could be affected by the amount of fat in the diet.
Adverse: Reduces drug effectiveness: When taking a medication, a food, nutrient, or other substance should be avoided as it may increase or decrease the medication’s absorption and/or activity in the body. Sometimes just having too much food in the stomach can block a medicine’s action, which can be avoided by taking it on an empty stomach.
Adverse: Negative interaction: When taking certain medications, a food, nutrient, or other substance should be avoided, as the combination may cause undesirable or dangerous interactions. It is generally recommended to avoid foods that have been shown to interact with a medicine.
Spotlight on some highly interactive foods
Drug interactions are not often studied, and animal and test tube studies, which don’t always translate to clinical effects, are often the primary sources of information. But following research over time has revealed some foods that should be avoided or taken with care when under medical treatment:
Grapefruit and grapefruit juice: By inhibiting an intestinal enzyme that helps metabolize many different drugs, grapefruit allows more of certain drugs to be absorbed, potentially increasing the medication’s effectiveness and the toxicity, even if the grapefruit is consumed at a different time than the drug. A few of the long list of interacting drugs include amlodipine, atorvastatin (Lipitor), cyclosporine, diltiazem, felodipine, lovastatin, methylprednisolone, nifedipine, sildenafil, simvastatin (Zocor), and verapamil.
Pomegranate and pomegranate juice: This fruit inhibits the same enzyme blocked by grapefruit. While there is much less research on drug-pomegranate interactions than on drug-grapefruit interactions, it would be reasonable to assume that the same interactions that occur with grapefruit would also occur with pomegranate.
Dark-green vegetables: These are rich sources of vitamin K, which interferes with the blood-thinner, warfarin. A person taking warfarin does not have to avoid vitamin K–containing foods. However, with the aid of a doctor or a dietitian the average vitamin K intake should be kept relatively constant from week to week.
The key to health is conscientious consumption
While the strength of research varies, there is enough data to suggest a number of other interactions between foods and drugs, such as:
Alcohol, which should not be mixed with certain medications
High-calcium foods which can block the absorption of some drugs
Black tea, some spices, beer, and nutrients such as resveratrol (found in red wine, nuts, and dark chocolate) have been found to have various interactions with medications.
To get the benefits of both a healthful diet and prescription medications, without exposing yourself to potentially harmful interactions, look for credible science-based information and talk to your doctor or pharmacist.
An expert in nutritional therapies, Chief Medical Editor Alan R. Gaby, MD, is a former professor at Bastyr University of Natural Health Sciences, where he served as the Endowed Professor of Nutrition. He is past-president of the American Holistic Medical Association and gave expert testimony to the White House Commission on Complementary and Alternative Medicine on the cost-effectiveness of nutritional supplements. Dr. Gaby has conducted nutritional seminars for physicians and has collected over 30,000 scientific papers related to the field of nutritional and natural medicine. In addition to editing and contributing to The Natural Pharmacy (Three Rivers Press, 1999), and the A–Z Guide to Drug-Herb-Vitamin Interactions (Three Rivers Press, 1999), Dr. Gaby has authored Preventing and Reversing Osteoporosis (Prima Lifestyles, 1995) and B6: The Natural Healer (Keats, 1987) and coauthored The Patient's Book of Natural Healing (Prima, 1999).