Purple-fleshed kumara could reduce the chance of colon cancer by up to 75 per cent, research shows.
Kiwi researcher Dr Khalid Asadi found the purple variety of the root vegetable, also known as a sweet potato, could prevent colorectal cancer when fed to mice in a variety of forms.
Asadi carried out the research at the University of Auckland almost 10 years ago but has only just been able to have his article published in the Journal of Cancer Prevention because of commercial sensitivity.
He found that when fed to three generations of mice bred with colon cancer, using the same gene which caused the disease in humans, purple kumara reduced the number of polyps by two-thirds or more.
Some mice were fed a mixture made with the skin of the kumara, others were given the same mixture but used the flesh of the vegetable and the mixture fed to a third group used a concentrated extract derived from the kumara.
The group given the mixture made with the anthocyanin-rich extract saw the greatest effect with a 75 per cent reduction.
Asadi said human trials had yet to be conducted but his research suggested the vegetable could reduce the chance of a person getting colorectal cancer, also known as bowel cancer, by up to 75 per cent.
Bowel cancer is the second highest cause of cancer death in New Zealand. In 2011, 3030 Kiwis were diagnosed with bowel cancer and 1191 died from the disease.
Asadi said the purple kumara used in the study had a high concentration of anthocyanin - the compound belongs to the flavonoid family and is a great antioxidant and anti-inflammatory.
While the food was a great preventative, most people would not eat enough of it to get the full benefit, he said.
"To eat 1kg of sweet potato every day is too hard."
But, the concentrated extract used in the study would also be an easy way for people to get all the benefits of kumara and said the powder could eventually be put into tablets, he said.
Asadi said others had also started to look into the health properties of purple-fleshed kumara but this was the first study to demonstrate the preventative effect of purple sweet potato using a model which was more relevant to human colorectal cancer, where the gene mutation was often inherited or occurred sporadically.
Similar studies had also found similar benefits from other purple fruit and vegetables including tart cherries, red grape and red cabbage but kumara was more widely and commonly eaten, he said.
The sweet potato was the world's seventh most important food crop on fresh-weight basis after wheat, rice, maize, potato, barley and cassava, he said.
More than 123 million metric tons were produced internationally per year and in Oceania, including New Zealand, the average yearly per capita consumption was estimated at 73kg - very high in comparison with other areas.