A study by the Western Australia Institute of Medical Research Epidemiology warns fruit juice drinkers of a risk of bowel cancer.

While the study by the institute, published in the Journal of the American Dietetic Association, found that eating more fruit and vegetables help reduce risk of distal colon cancer, fruit juice's high sugar content actually increases the risk of certain cancers.

At higher risk to develop rectal cancer were people who drank more than three glasses of fruit juices a day.

The researchers explained that after processing and packaging, ingredients in fruit juice that protect against tumours, such as fibre, vitamin C and antioxidants, are lost. But vegetables such as broccoli, sprouts, cauliflower, apples and dark yellow vegetables helped battle proximal and distal colon cancers.

The study was based on comparison of 918 colorectal patients and 1,021 control patients.

"The study looks at the same disease in a different way to back up the idea that eating lots of fruit and vegetable and maintaining a healthy body weight causes a decrease in the risk of all types of cancer, diabetes and heart diseases," Cancer Council spokesman Terry Slevin told The West Australian.

Department of Health guidelines advise intake of five portions of fruit and vegetables daily, including a glass of juice.

Previous research by Bangor University in Wales found it would be better for people to eat prunes or other dried fruit instead of freshly squeezed juice which has up to five teaspoons of sugar per glass.