Certain drugs have labels that warn they shouldn’t be taken with grapefruit because it lessens their potency.
Preliminary research from the University of Wisconsin's Medical School suggests some artificial sweeteners could affect the way the body metabolises particular drugs, including antibiotics, antidepressants and antivirals.
The lab-based study showed that the artificial sweeteners (sucralose and acesulfame potassium) disrupted the function of a protein in the liver that helps remove toxins and drugs from the body.
Registered nutritionist and professional practice fellow at the University of Otago Ali Hill speaks to Jim Mora about the various relationship between foods and medication.
Photo: 123RF
Dr Hill says the two artificial sweeteners identified in the US study were well-controlled in Aotearoa by Food Standards Australia New Zealand.
“The study that they did was in cells, so we don’t know quite how that relates to having it in our bodies because we don’t feed cells, we feed ourselves.”
On grapefruit’s interaction with drugs, she says this is more likely to do with the juice than the fruit itself.
“The issue here is that if you have a grapefruit, you eat one grapefruit. If you’re making a juice, it takes several grapefruit to make that juice so in effect all of the compounds, the furanocoumarins, that stop the absorption [of certain medications] and interfere with them are more concentrated.”
There are probably more than 80 drugs that can create this grapefruit compound, she says, but medications affected by this should have a warning in the instruction pamphlet or label provided.
Dairy products can also interfere with antibiotic absorption, she says.
“I think it’s something that’s not very well known but what basically happens here is the antibiotics link to calcium that you find in your dairy foods and they make this kind of compound that you can’t absorb, so basically there’s less of the antibiotic in your body, so it means it’s less effective that way.”
But Dr Hill cautions that various antibiotics have different advice about whether it’s best to consume with food or without, so it’s best to follow the instructions provided or check with your pharmacist if unsure.
Similarly, eating cereals fortified with iron or magnesium can reduce absorption of certain antibiotics, she says.
“What happens here is the iron or magnesium bind to the antibiotic so it can’t be absorbed but … you need to balance up your options.
“A lot of people don’t have enough iron anyway so we don’t scare people off having these foods that are fortified with iron, because we actually want to make sure people are still getting enough and they’re not getting iron deficiency and anaemia.
“So perhaps it’s more thinking about the timing of when you’re having these foods and antibiotics rather than just not having these fortified foods because they’re really, really valuable for us.”
Timing can also be crucial to consider with contraceptive pills and sugar-free sweets, she says.
“You may have seen the warnings that come on the side of sugar-free sweets or lollies that say about them having a laxative effect.
“The issue here is that the gut is where you absorb some of your drugs from and so the speed that it goes through your gut means that there’s less time for it to be absorbed.
“The thing with a contraceptive pill is that it’s very time-dependent so you have to kind of keep a constant level in your body and you do that by taking it a certain time, so this is why it can have such a big impact on the effectiveness.”
Consuming foods with high potassium along with drugs for high blood pressure may create issues, she says.
“What happens here is that certain types of drugs actually cause you to store potassium in the kidneys more and if you are having foods, like bananas, that have really high potassium levels, then that can cause an issue as well. So, you might get things like weakness, fatigue, and then your heart rhythm can be abnormal as well.”
On the other hand, dairy may help counteract a side-effect of some medication for type 2 diabetes, Dr Hill says.
“If you are on metformin, this will reduce the amount of vitamin B12 absorption. And dairy is a really, really good source of B12, so by having dairy you’re kind of counteracting those effects.
“An important thing to note here as well is that if you’re on reduced fat dairy, there’s the same amount of calcium as there is in full-fat options as well.”
These issues are coming to the fore nowadays as we look more widely at the compounds that can influence absorption of medicine, Dr Hill says.
“What we can do is somebody can take a medicine and they can take it at the same time as a certain food or drink and we can measure how much of the drug is actually in your body afterwards and we can use that to try and see what types of foods and drinks, or things that are in foods and drinks, can actually influence how well a drug works or not.”
