Eat kiwis and loosen up

August 18, 2000

The antioxidant properties of kiwi fruit could have a beneficial impact on health

Kiwi students are eating their fruit namesake in the name of science. Researchers from the University of Auckland and Auckland University of Technology are studying the laxative properties of the kiwi fruit, which has become one of New Zealand's best-known exports.

About 50 AUT students have been recruited to feast on kiwis - eating up to two or three a day, depending on their body weight.

"There have been anecdotal reports that kiwis have good laxative properties," explains Lynnette Ferguson, associate professor in the Auckland Cancer Society Research Centre at the University of Auckland. "This could be useful for an elderly population, but we first want to quantify the effect."

Working with colleagues at the Rowett Research Institute in the United Kingdom, Ferguson is also keen to explore the antioxidant properties of kiwis. Preliminary data from the Rowett have shown that a large, concentrated dose of kiwi fruit in a short time appears to reduce DNA damage in human blood cells and may have a beneficial impact on health.

The Auckland researchers want to know whether similar effects can be achieved by eating a normal diet that includes kiwis.

But kiwis are not the only fruit - vegetables and other natural products are under the spotlight in New Zealand's universities.

Low rates of colon cancer among the Maori population have left scientists pondering the potential cancer-suppressing properties of kumara, or sweet potatoes. Maoris eat higher quantities of kumara as a starch source than New Zealand's Europeans.

Ferguson and colleagues have shown that feeding laboratory animals whole kumara appears to suppress tumour cell growth in the late stages of cancer.

Now they have isolated compounds from the sweet potatoes that may act as the antioxidants responsible. The next stage is to test these compounds in another round of animal experiments.

Honey's bacteria-busting properties are also being investigated.

According to Peter Molan, director of the Honey Research Unit at Waikato University, honey has been used for more than 4,000 years as a wound treatment.

Scientists know that the hydrogen peroxide that is produced when honey ripens or is diluted kills bacteria. But high levels of it can cause inflammation of tissue, so it is generally not favoured for treating wounds. But in honey it does not appear to damage tissue.

Molan says: "Honey appears to tie up metals, such as iron and copper, which normally catalyse the breakdown of hydrogen peroxide to form free radicals that cause the inflammation. It is presumably the polyphenols and flavonoids in honey that bind to the metals, but that remains to be investigated."

Working in collaboration with the Central Public Health Laboratories near London, Molan has also found that honey is effective in suppressing superbugs - the antibiotic-resistant bacteria that scientists fear may soon make some medicines redundant.

"We used honey on bacteria isolated from people with various strains of superbug and found it could be diluted 20 times and still be effective against the bugs."

The New Zealand team, working with UK colleagues, is also looking to develop better methods of applying honey to wounds.

"It's a challenge keeping it in place," Molan says. "If liquid seeps from the wound, it becomes runny and sticky."

The idea is to absorb honey into the dressing, creating a new composite. One such material is being patented by Waikato University.

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