Among people who have a genetic susceptibility to colon cancer, those whose diets are heavy in junk food have an even higher risk, according to a new study.
"These patients have this very high risk because of this (genetic) mutation they have, but it might be that they could reduce the number of (tumours) by having a more healthy lifestyle," said Akke Botma, the lead author of the study.
Botma's study is just the first to find a link between certain foods and a higher colon cancer risk in this group, and it can't prove that the diet is to blame.
All of the people in the study had Lynch syndrome, a genetic disorder that predisposes people to cancer at younger ages and that affects up to one in 660 people.
In Western countries, colorectal and endometrial cancers are the dominant cancers to turn up in people with the syndrome, while in Asia it's mostly stomach cancer, Botma said.
Up to 70 percent of people with Lynch syndrome will develop colon cancer. Among people without Lynch syndrome, such cancers are thought to be influenced by diet, particularly alcohol and red and processed meat, the authors note in their study, published in the journal Cancer.
Botma and her colleagues at Wageningen University in the Netherlands contacted 486 people with Lynch syndrome from a national database of families with inherited risks for cancer.
At the beginning of the study they surveyed the participants about what they ate, and they ranked each person on whether he ate low, medium or high amounts of foods within four dietary categories.
The food groups included one that was dominated by fruits, vegetables and whole grains; another that was high in meat and coffee; a third dietary group that resembled a Mediterranean diet - fish, leafy greens, pasta, sauces and wine; and a fourth group that was heavy on fried snacks, fast food and diet soda.
Botma and her colleagues found that, over 20 months of follow up, 56 of the participants -- or 12 percent -- screened positive for tumours in the colon, a precursor to cancer.
Of the four dietary groupings, only the junk food category showed any link with a different risk for developing colon tumours.
Of the 160 people who scored low on the junk food diet, 17 developed tumours, while 18 out of the 160 people who ate the most junk food developed tumours.
The numbers initially seemed similar, but after taking into account smoking and other risk factors, the researchers determined that those in the high junk food group were twice as likely to develop colon tumours.