An apple a day might keep the doctor away, provided you eat the peel. But not all fruit is as good for us as we are led to believe.
A review article published in the Canadian Medical Association Journal reveals that a chemical in grapefruit increases the risk of overdosing on certain medications, and can prove potentially fatal.
It has been known for some time that the chemical in certain citrus fruits (including grapefruit, lime, pomelo and bitter orange such as the Seville) blocks the enzyme that breaks down some drugs. But the new review reveals the number of drugs that interact badly with grapefruit is higher than previously thought. They include some antiobiotics, statins, heart and cancer medications.
"We've known about it interacting with certain medications for a while," said Kathy Chapman, chairwoman of Cancer Council Australia's nutrition and physical activity committee. "Now it is a much wider list . . . Grapefruit is a seemingly innocuous type of food, but sometimes, particularly when concentrated as in grapefruit juice, it leads to high levels of the medicine in the bloodstream and that could cause problems."
The information comes at a time when the health benefits of fruit are already in question. It is packed with sugar, specifically with fructose, a type of sugar that,in excess, numerous studies have linked with obesity and found to have a harmful effect on the liver.
And despite the current dietary guidelines to eat more fruit and vegetables to "reduce the risk of chronic diseases such as . . . some types of cancer", a 2009 study of more than 400,000 people found that fruit and vegetable intake does not reduce the overall risk of cancer.
Despite this, we shouldn't cut back, Ms Chapman said. While being overweight or obese is directly linked to cancer, eating fruit and vegetables can indirectly reduce the risk. They contain an array of vitamins and help us achieve our daily intake of fibre. "Dietary fibre has been shown to be protective against bowel cancer," Ms Chapman said. Plus, "fruit and vegetables help to maintain our weight . . . The latest research shows about half Australians get their two serves of fruit [a day] and only one in 10 have their recommended five serves of vegetables a day."
She expects that upping our fruit and vegetable intake will still be a "mainstay message" when the new dietary guidelines are released early next year. A statement by the National Health and Medical Research Centre, which is behind the guidelines, confirms this.
"A large number of experimental studies using dietary modelling have provided evidence of a protective effect of fruits and vegetables against these non-communicable chronic diseases."
The benefits of fruit "range from reduced formation of cancer-promoting substances in the gastrointestinal tract [through antioxidant activity], to the part played by phytochemicals and micronutrients in detoxification of carcinogenic substances, and to functions relating to the containment and destruction of existing cancer cells by means of a variety of physiological effects".
In addition to this, "these foods are nutrient dense, relatively low in energy [kilojoules] and are good sources of minerals and vitamins, dietary fibre and a range of phytochemicals".
The dietary guidelines are not set to change their message about fruit in general. As for the specific problems relating to citrus fruits and medications, "the main message about grapefruit, when on medication, is check the packaging", Ms Chapman advises. "Warnings about grapefruit juice will be included [on the packet]. Also, a quick word to your local pharmacist or doctor will dispel any concerns you might have."