Food-drug interactions: should we be concerned?

By Dr. Ross Walker
October 2020

The human body is such a complex structure and is working all the time to keep us in balance. This requires the coordination of thousands of different proteins and other natural chemicals interacting on a moment by moment basis. When something goes wrong in the body, this typically manifests as symptoms and a subsequent disease. Enter the medical profession!

Much of medical teaching is based around the therapeutic value of pharmaceutical drugs and a variety of surgical procedures. Basically, if you can’t fix it with a prescription pad or a scalpel, then any other approach doesn’t work. I have been saying for many years that the five key lifestyle principles are four times more powerful than anything a doctor can do for you, but, when you have an established medical disease, it is also important to have medical therapy.

There is no doubt many of the pharmaceutical treatments that are administered to people may have significant interactions with other aspects of our life. One very well recognised scenario is the interaction between a variety of foods and commonly prescribed pharmaceutical drugs. Let’s focus purely on pills (I’m leaving out intravenous therapies for the purpose of this article) which are swallowed to have their therapeutic effects. The process of swallowing food, pills, vitamin supplements and herbs, along with the variety of fluids people ingest throughout the day, may lead to significant interactions that strangely may either have no effect on the drug involved, increase or decrease its activity, depending on a number of factors.

Certain foods and supplements may affect how well a drug is absorbed either increasing or reducing absorption based on the mechanism involved. At other times, specific foods and supplements may affect a number of biochemical mechanisms within the gastrointestinal tract and specifically the liver where all of our raw materials are metabolised and again may either increase or decrease the activity of the prescribed pharmaceutical drug. Alternatively, a number of drugs are excreted in the kidneys with a number of factors affecting the efficiency of this mechanism.

Without getting too detailed, I thought I would list a number of commonly prescribed medications and the potential foods and timing of the ingestion of these foods and fluids that may affect the drugs.

1) Warfarin: this drug has been around for many years and has been the workhorse strong blood thinner for people with artificial heart valves, a specific cardiac abnormality-atrial fibrillation and recurrent clotting in veins known as deep venous thrombosis and/or pulmonary emboli.

Thankfully, there are a handful of newer drugs which don’t require the diligence needed to achieve proper levels of warfarin in the bloodstream. Unfortunately, these new drugs are not replacements for people with artificial heart valves but are highly effective for the management of atrial fibrillation and recurrent clotting.

When you are on warfarin you have to be very careful with what you eat, what you drink, other medications and certain supplements. The big interaction is with certain medications such as some painkillers, a number of antibiotics and specific food stuffs such as leafy green vegetables which are loaded with vitamin K which compete directly with the action of warfarin. Alcohol can also affect the way warfarin is metabolised in the liver. The strong message here is that if you need to be on warfarin, you need to be very careful and have a strong line of communication with your doctor about all of the above.

2) Calcium rich foods and antibiotics: the commonly prescribed antibiotics such as the tetracycline group and another antibiotic-ciprofloxacin, are affected by taking these with milk and other calcium rich products. The calcium binds the drugs in the gut and there is a marked reduction in absorption.

3) Pickled, cured and fermented foods interact with some old-style antidepressants which are not commonly prescribed these days known as monoamine oxidise inhibitors: these foods, especially cheese, are loaded with tyramine which can markedly increase the activity of these drugs. Some drugs prescribed for Parkinson’s disease can also be affected by this mechanism and it is very important to discuss with your doctor what food you should eat if you are prescribed any of these therapies.

4) Alcohol and a number of prescription medications: In particular sedatives, painkillers and stimulants. If you are prescribed any of these medications you should be very careful about your alcohol intake limiting this to no more than two small glasses per day, if at all. Alcohol can also affect a number of other therapies such as antibiotics. If you enjoy a drink & are prescribed medications, always discuss this with your doctor & pharmacist.

5) Grapefruit juice and just about any medications: As we all reach that milestone of 60, I would suggest it is more the exception than the norm that we are on medications for something. Grapefruit juice is a strong inhibitor of the main enzyme system that breaks down a number of commonly used drugs. It reminds me of the joke when the little boy says to his mother, “When I grow up I want to be a rock musician”. His mother replies, “I’m sorry but you have to choose one or the other”. In the same way, over the age of 60 I believe we should be avoiding grapefruit juice if we are on any medications whatsoever and in particular statin drugs, some BP medications and some drugs used for treating mental health disorders.

6) Bananas and BP treatment: There are two commonly prescribed BP pills known as ACE inhibitors and ARBs. Bananas have a relatively high concentration of potassium and these two blood pressure groups may elevate your potassium somewhat. If you enjoy bananas, and your blood pressure is high, it is important to have your potassium levels measured (which should be done regardless because you have high blood pressure) along with your kidney function. If your potassium is above the normal range you should reduce your intake of potassium containing foods such as bananas and tomatoes. This is not a particularly significant issue for most people.

In most cases simply take your medications one hour before or two hours after eating and if you are on any of the medications I have mentioned such as statins for cholesterol, blood pressure pills, treatment for diabetes, reflux drugs, painkillers, sedatives and antidepressants, ask your doctor and pharmacist to give you a full list of the foods you can enjoy and the food you should avoid.

This straightforward conversation may be the difference between the prescribed medications working, having no effect or potentially very serious side-effects based on the drugs and the food involved. We have long since passed the era where doctors were dictators and we basically did what we were told. We are now in the era of information which is available to us all and, in my view, doctors should be two things to patients: educators and servants. The long-term management of any chronic condition requires a careful analysis of all aspects of a person’s care which includes the food, fluid and supplements they take and the potential for interactions for any medications that may be prescribed.



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