"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 (tumors) 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 tumors 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 tumors.
Of the 160 people who scored low on the junk food diet, 17 developed tumors, while 18 out of the 160 people who ate the most junk food developed tumors.
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 tumors.
HOW TO MANAGE RISKS?
"It's hard to say why" junk food is linked with a greater risk for these tumors, said Dr. Mala Pande, an instructor at the University of Texas MD Anderson Cancer Center in Houston who was not involved in the research.
She said some researchers have suggested that high fat might have something to do with it, but it's impossible to conclude that from this study.
Although the findings are too preliminary to be used in making dietary recommendations to people with Lynch Syndrome, the study was valuable in launching research into the possible role of certain foods on cancer risk, said Christopher Amos, a professor at the Geisel School of Medicine at Dartmouth College.
"People with Lynch Syndrome are at higher risk, and we'd really like to know how to manage their risks better," Amos, who was not part of the study, told Reuters Health.
Certain foods have been shown to be linked with different types of cancer, but many of those studies contradict each other and sow confusion.
Amos said the new study is a good start, but "it would be nice to confirm (it) with additional findings."