Debates on associations of nutrients with disease risk are common in the literature and attract attention in public media; however, new research published in the American Journal of Clinical Nutrition casts doubt on many reports linking certain foods to increases or decreases in cancer risk.
Researchers from the Stanford Prevention Research Center and Harvard Medical School sought to examine the conclusions, statistical significance and reproducibility in the literature on associations between specific foods and cancer risk. They selected 50 common ingredients from random recipes in a cookbook, and used PubMed to identify recent studies that evaluated the relation of each ingredient to cancer risk.
Forty out of the 50 ingredients had articles reporting on their cancer risk. Of the 264 studies, 103 studies suggested the food ingredient was tied to an increased risk of cancer and 88 to a decreased risk. The average effect shown in each study was about a doubling of cancer risk or a halving of risk, depending on which direction the association went for a particular ingredient in a particular review. However, the evidence backing those claims was usually weak, the researchers said. In larger reviews that included multiple studies, the links between each particular food item and cancer risk were typically smaller or nonexistent.
"We have seen a very large number of studies, just too many studies, suggesting that they had identified associations with specific food ingredients with cancer risk," said lead author Dr. John Ioannidis from the Stanford Prevention Research Center in California, in a statement to Reuters. "People get scared or they think that they should change their lives and make big decisions, and then things get refuted very quickly."
