Nutrition
A bad mix
by Jennifer Bowden
Grapefruit interacts badly with some medications. Should you be worried?
Question: People taking some cholesterol drugs (eg, Lipex) are advised not to eat grapefruit because it contains some chemical that negates their effectiveness. However, I understand this research was done in the US, presumably with their grapefruit. If it was with the large, pale yellow, slightly bitter variety, they are different from New Zealand Grapefruit (once called Poor Man’s Orange and sometimes called Gold Fruit). Has any research been done on the New Zealand Grapefruit? (F Coulter, via email)
Answer:
This issue has prompted lots of letters to this column and to Peter Calder’s Any questions (March 29). Sir George Grey introduced grapefruit into New Zealand in the 1850s. The slightly bitter flavour but heavy cropping quality of this yellow-skinned, orangy-fleshed fruit led to the label “Poor Man’s Orange”. It was renamed New Zealand Grapefruit in the 1920s, but this was changed to Gold Fruit in the 1980s − hence the confusion.
Food interactions with prescription drugs are concerning because they can lead to treatment failure, resulting in medication being less effective or more bioavailable – which means the medication becomes more concentrated in the body, potentially increasing the risk of an adverse reaction or overdose.
Grapefruit interacts with a number of prescription drugs by inhibiting enzymes and transporters involved in the breakdown and clearance of medications in the gut. This results in an accumulation of certain medications and has a greater effect than what was planned or prescribed. And the effects are not short-lived: one glass of grapefruit juice may inhibit drug metabolism for up to three days.
Although the inhibitory effects are well-documented, less is known about the compounds in grapefruit responsible for these effects. It is thought flavonoid glycosides, furanocoumarins and sesquiterpenes are the most likely causes.
A University of Otago research team looked into the presence of two flavonoid glycosides and one furanocoumarin in grapefruit from supermarkets in Dunedin. Their findings were published in 2000 in the Pharmaceutica Acta Helvetiae.
Several types of grapefruit were analysed, including one named as New Zealand Grapefruit that was found to have significant quantities of flavonoid glycosides and furanocoumarins – enough to affect drug metabolism.
University of Otago researcher Dorothy Saville couldn’t confirm whether the New Zealand grapefruit used in the study was Poor Man’s Orange. But the research team could confirm that, irrespective of grapefruit variety, there was considerable variation in furanocoumarin and flavonoid-glycoside content.
“It is likely that furanocoumarin content may vary a great amount depending on growing conditions and maybe even the area of the country in which a particular variety is grown – eg, Auckland versus Invercargill or wet season versus dry season,” says Saville.
There is still much to learn about grapefruit, and Saville suggests that once the inhibitory compounds are more fully understood, further research should be done to determine which varieties contain the compounds.
As the number of inhibitors in grapefruit is unknown – and can vary from season to season depending on fruit variety and growing conditions – it is important to be cautious.
You should avoid all grapefruit varieties and products – whole fruit, juice and jams – if your medication warns against consumption.
Email: nutrition@listener.co.nz, or write to “Nutrition”, c/o Listener, PO Box 90783, Auckland.
