People under 50 are experiencing an alarming rise in bowel cancer, and a diet of too much meat and fast food may be to blame, cancer experts in the United States say.

Bowel cancer incidence rates have remained stable or decreased in older people for more than a decade in the US, largely due to screening tests such as colonoscopies, which are recommended for people over 50.

However the study, published by the American Cancer Society yesterday, found incidence rates of colorectal cancer in those aged 20 to 49 increased 1.5 per cent a year in men and 1.6 per cent a year in women between 1992 and 2005.

The biggest rise was seen in those under 30, where rates rose by 5.2 per cent a year in men and 5.6 per cent a year in women. In sharp contrast, rates for the over-50s are now dropping 2.8 per cent a year in men and 2.2 per cent a year in women.

The researchers said rising levels of obesity, and changes in diet towards more fast food, red and processed meat, and less milk over the past three decades might have contributed to the increase in colorectal cancer among young adults observed in the study.

Last week a study by The George Institute at the University of Sydney found people who had two or more alcoholic drinks a day or more than seven drinks a week had a 60 per cent greater risk of developing colorectal cancer compared with teetotallers.

Professor Graham Newstead, chairman of the Colorectal Foundation, said the lack of awareness among Australians about bowel cancer was shocking.

Bowel cancer is the most common cancer in Australia to affect both men and women, with about 13,000 diagnoses and 4000 deaths annually. Historically, the risk has increased with age.