A study published in the American Journal of Clinical Nutrition reveals that studies linking food to cancer risk may be debatable.
For the study, the Harvard Medical School researchers selected the first 50 ingredients they found in randomly-chosen cookbook recipes. That list included meats and fish, vegetables, dairy products, bread, and spices. The researchers ran each ingredient through a medical journal database search to see if there were any studies tying how much of it people consumed to their risk for some type of cancer. For 40 out of the 50 ingredients—including veal, celery, cheese, and mustard—there were a total of 264 such studies. Of those, 103 suggested the ingredient was tied to an increased risk of cancer, and 88 to a decreased risk.
Studies on some ingredients, such as onions, carrots and tea, almost all showed a decreased cancer risk, and for others, like bacon and sugar, most or all findings showed a higher risk. But for many foods, study results were all over the map. 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 report. However, in larger reviews that included multiple studies, the links between each particular food item and cancer risk were typically smaller or nonexistent.
The authors recommend people to not over-interpret individual studies and instead to look to guidelines that have been published based on more comprehensive reviews.