Most food-cancer links unproven, says new study

American research finds cancer food scares don’t stand up to scrutiny with most culprit ingredients showing little or no increased risk of disease.

They are mainstay stories of tabloid newspapers and women’s magazines, linking common foods from burnt toast to low-fat salad dressing to cancer. But now US scientists have warned that many reports connecting familiar ingredients with increased cancer risk have little statistical significance and should be treated with caution.

Dr Jonathan Schoenfeld of the Harvard School of Public Health has published a new study in the American Journal of Clinical Nutrition that says trials have failed to find effects for observational studies that link foods with cancer. Everything from low fat salad dressing to celery, olives, and sugar has been linked to cancer development in observational studies.

The scientists chose 50 random ingredients from the Boston Cooking-School Cook Book then searched each ingredient to find associations with cancer risk in medical literature. They found that 40 foods, including flour, coffee, butter, sugar, peas, duck, tomatoes, lemons, onions, carrots, parsley, lobster, veal, cinnamon, and mustard, had been studied as being possible carcinogens. The ten that were not studied were uncommon ingredients.

The papers written about the carcinogenic properties of these foods were analysed, including statistical significance and how each food actually increased cancer risk. Most of the reports found no valid medical pattern. In fact, 75% of the risk estimates had “weak or no statistical significance”. The full text of the study usually presented more conservative results than the study abstract.

In other words, one individual study that finds a link with cancer is usually difficult to repeat. More than one valid peer-reviewed study is needed before a conclusion about cancer causation can be reached.

“We found that, if we took one individual study that finds a link with cancer, it was very often difficult to repeat that in other studies,” said Schoenfeld. “People need to know whether a study linking a food to cancer risk is backed up before jumping to conclusions.”

Source: The Guardian