16 Dec 2016

Obesity responsible for 10 percent of bowel cancers

7:35 am on 16 December 2016

Obesity is responsible for one in 10 cases of bowel cancer in this country, public health researchers say.

Bootcamp weigh-in time

Photo: RNZI/Sally Round

3000 New Zealanders are diagnosed with bowel or colorectal cancer a year and 1100 die from it - a rate among the highest in the world.

Lead researcher and public health specialist Ann Richardson said nine percent of cases were attributable to obesity and seven percent to alcohol.

Other risk factors included:

  • Red meat consumption (five percent of cases)
  • Processed meat consumption (three percent)
  • Physical inactivity (four percent)
  • Smoking (three percent)

The researchers identified those risk factors with strong evidence of causation, not just correlation, Dr Richardson said.

"That's allowed us to calculate the percentage of bowel cancer that potentially could be avoided."

The estimates were similar to those for Australia and the United Kingdom.

Results could vary by ethnic group, which wasimportant in targeting future public health initiatives, she said.

"For Pacific women, for example, 19 percent of bowel cancer can be attributed to obesity, and for Maori women 14 percent - whereas for European women and other women it's eight percent."

The results were likely to be under-estimates rather than over-estimates, she said.

Otago University professor of colorectal surgery Frank Frizelle said bowel cancer occured in people of all sizes.

Five to six percent of cases would be hereditary and one to two percent related to inflammatory conditions, leaving about 90 percent known as "sporadic bowel cancer", he said.

That was what Dr Richardson and others had focused on, he said.

"It's probably how you got obese, about the consumption of the foods that got you there.

"But obesity is something you can measure, something that in their study they show stands out - but it is probably how they got there over a period of time that is actually more relevant."

That was likely to be about what people ate and how that interacted with gut bacteria, for example, he said.

"What you eat alters the virulence or the activity of the bacteria in your colon, and if you happen to have the right bacteria or the right environment it's possible or probable ... that that will create the right environment for cancer to develop."

Bowel Cancer New Zealand spokesperson Sarah Derrett said more help was needed to ensure all New Zealanders ate well.

"Luxuries have become affordable, and essentials - healthy fruit and vegetables - are increasingly expensive and difficult for people to factor into their daily budgets. We need to turn that around."

Dunedin cancer specialist Chris Jackson, says said it was time that politicians accepted that individual responsiblity was not a sufficient answer to the growing cancer burden.

"It is within the government's powers to do something about the risk factors for cancer and if we bind together and we have good strong policies for public risk factors then we can potentially change the game."

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