Grapefruit, broccoli, dairy and more: here’s what you need to know about the main contraindications between food and drugs

©FRANK FIFE/AFP

Atlantico: How important is diet when taking prescribed antibiotics?

Beatrice de Raynal: How can a food consumed in a portion of 100 grams or more have no effect on our physiology, while taking a few milligrams of medicine will be enough to change the state of health in the desired direction?

Obviously, certain interactions do exist and should be avoided either for the medication to work properly or to prevent nutrient absorption or metabolism from being affected.

What eating style is usually recommended when taking medications? Why are foods like grapefruit not recommended in some cases? What other contraindications?

When you take a medicine, is the dose given actually absorbed in the intestines?

Drug-food interactions are determined by changes in bioavailability: they influence the effectiveness or toxicity of a drug through food, herbal extracts and dietary supplements. The best known is the role of grapefruit and its derivatives, St. John’s wort and other medicinal plants.

Warfarin, used to prevent and treat blood clots, has been widely prescribed in the UK since the 1950s. So why might eating certain vegetables cause concern?

More than 30% of Americans use at least one dietary supplement, a third of which contain medicinal herbs. One third of Americans who consume these herbal medicines and dietary supplements are also taking oral medications.

The consequences are often sad: either the medicine stops working, and in the case of chemotherapy it is still annoying, or the effect of the medicine increases, which is no better! Either the mixture causes unprecedented toxicity unknown to the physician, or finally the mixture produces an exponential effect.

Therefore we have several options:

• lack of interaction. The substances do not interfere with each other at all;
• enhancing the effect of one of the drugs, which is then potentiated. This is the case, for example, with some drugs used in anesthesia to cause muscle relaxation. The effect may also be enhanced by certain antibiotics;
• mutual enhancement of the effect of two substances. For example, the simultaneous use of drug treatment and anti-allergy dietary supplements called antihistamines, especially when adding benzodiazepines, against anxiety…. Sleep guaranteed!

Should medications be taken before, during, or after meals? Why is it important?

Digestion and its disorders sometimes play a role in indigestion by changing the acidity of the stomach. After eating, this acidity increases. Some medications are then less easily absorbed. Eating foods rich in fat can either impede the absorption of drugs, or, conversely, improve their absorption without increasing their toxicity (in particular, antiviral drugs).

We also know that aspirin and non-steroidal anti-inflammatory drugs such as ibuprofen taken on an empty stomach provide a faster effect, but often with a stomach reaction, taking with food avoids this inconvenience.

If you are taking vitamin K anticoagulants, it is important not to eat foods rich in them, such as organ meats, cabbage of all kinds, leafy vegetables such as spinach, or salads.

Grapefruit or its juice acts on an enzyme located in the liver and intestinal wall and increases the absorption of some cholesterol drugs and statins, as well as some immunosuppressants, some heart drugs, etc.

Be careful with licorice and all medications that limit or lower blood pressure: yes, it’s licorice, but also aniseed drinks, which are also very high in sodium for some. Without naming the brand, Ricard is not recommended as Berger is more acceptable to a person undergoing blood pressure treatment.

Beware of antioxidants proposed for anti-aging and cancer treatments, for example, which they weaken.

In conclusion: any drug treatment must be monitored, in particular, carefully read the instructions, which are very precise.

Sources: Drug-Food Interactions in Internal Medicine: What Doctors Should Know S. Mouly, M. Morgan, A. Lopez, C. Lloret-Linares, J.-F. Bergmann.