Who would have guessed that the foods we eat can affect the way that our medications work? Often when you see your doctor, they may neglect mentioning all the possible interactions with your prescription. The fact is that many foods can actually affect the way our bodies change, use and breakdown various medicines. Different foods can alter how quickly medicines are digested, the absorption of drugs from the small intestine, and the time it takes for the liver to break down various drugs.
Did you know that your morning grapefruit could increase the side effects you experience from certain medications? Are you aware that eating broccoli might reduce how quickly certain medicines will work? If not, read on.
Foods that influence your stomach
Foods which contain high fat and protein take longer to digest and require more processing time in the stomach. Fats stimulate our stomach to produce more acid. The result is a decrease in the effectiveness of drugs which are sensitive to acids, (such as penicillin). Carbohydrate (starch and sugar) rich meals can slow stomach emptying by altering how food is propelled along the gut (1). Foods high in fiber, such as broccoli, also slow down the time it takes for your stomach to empty because the indigestible parts of this vegetable will remain in the stomach a long period. Taking medicines on an empty stomach with a glass of water can increase how quickly a drug will work, however this might not always be desirable with some medications. For example, anti-inflammatory drugs (NSAIDs) can cause stomach upset if taken on an empty stomach, but this can be avoided by taking the medication after a small snack.
Foods that influence absorption
In some cases, certain medications can end up binding to other foods or medicines. This can result in poor absorption of the medicine and make it less effective. A classic example of this is taking medicines with antacids. Antacids may often bind with vairous medicines, slowing down the absorption from the small intestine and reducing the effectiveness of the medicine. Taking medicines with food high in fibre may cause the same result.
Another food group to be careful of when taking your medication is dairy foods. Some antibiotics such as tetracyclines (e.g. oxytetracycline, doxycycline, limecycline) and quinolones (e.g. ciprofloxacin) bind to various chemicals in dariy products. Supplements containing calcium or iron cause the same interactions. This can be avoided if the medication is taken 2-3 hours after taking dairy products.
Foods that influence the liver
The breakdown or modification of drugs can be significantly reduced or increased by certain food products. Currently, grapefruit juice causes the most clinically relevant of these interactions (2). Specialised cells within the liver breakdown and modify drugs; these cells can be either induced or inhibited by certain foods. Foods which act as inducers increase the activity of the specialised cells in the liver. This leads to a decreased level of the drug in the blood stream, therefore making it less effective. Foods which act as inhibitors decrease the activity of the specialized cells within the liver, leading to an increased level of drug. This will increase your risk of side effects.
Cruciferous vegetables, such as brussels sprouts, cabbage, and broccoli, contain substances which induce liver cells, and therefore they may decrease the effectiveness of various medicines.
Grapefruit juice has been shown to affect the metabolism of several drugs. It is thought that grapefruit juice influences not only the liver, but also intestinal cells. Grapefruit juice acts as an inhibitor. It can increase the levels of the drug inside your circulatory system, and this can lead to toxic side-effects.
The list below shows some common drugs which interact with grapefruit juice and the possible implications
The effect of grapefruit juice lasts about three days. If patients have other underlying medical conditions, the side effects could last even longer. To avoid grapefruit juice interactions, patients should abstain from this particular fruit and it's juice.
Miscellaneous drug-food interactions
Tyramine is a naturally occurring amino acid found in many food products, such as cheese, fruit (grapes, oranges, plums and raisins), processed meat, soya products and many nuts. Patients taking monoamine-oxidase inhibitors (phenelzine, isocaroxazid, and tranylcypromine) for depressive illness should avoid taking foods containing tyramine. This combination can result in a potentially serious interaction called the “cheese reaction.” The cheese reaction causes a dangerous rise in blood pressure along with a throbbing headache. Patients should be advised to avoid food that is suspected of being stale as tyramine levels build up over time This is especially important with meat and fish. The danger of interaction persists for up to two weeks after treatment with monoamine-oxidase inhibitor is discontinued.
Warfarin is an anticoagulant, or a medicine that stops blood from clotting. Anticoagulation therapy is initiated when there is risk of forming a blood clot (thrombosis). The blood needs vitamin K to clot. Warfarin slows the production of vitamin K in the body, which increases the time it takes for the blood to clot. Food products containing vitamin K, such as green vegetables and soya bean products can reduce the anticoagulant effect of warfarin when consumed in large quantities. There is also evidence to suggest that the same may be true when concerning large quantities of ice cream.
Fish oil supplements, on the other hand, can greatly enhance the effect of warfarin. Patients taking warfarin should abstain from these types of supplements while on the medication.
Conclusion
There are many types of interactions that can occur between foods and medicines. As with any medicine, if are unsure of something, always speak to your pharmacist or the prescriber and always read the patient safety leaflets that come with your medication.
