A trip to almost any bookstore or a cruise around the Internet might leave the impression that avoiding cancer is mostly a matter of watching what you eat. One source after another promotes the protective powers of “superfoods,” rich in antioxidants and other phytochemicals, or advises readers to emulate the diets of Chinese peasants or Paleolithic cave dwellers.Eat what you want; die anyway.
But there is a yawning divide between this nutritional folklore and science. During the last two decades the connection between the foods we eat and the cellular anarchy called cancer has been unraveling string by string.
This month at the annual meeting of the American Association for Cancer Research, a mammoth event that drew more than 18,500 researchers and other professionals here, the latest results about diet and cancer were relegated to a single poster session and a few scattered presentations. There were new hints that coffee may lower the risk of some cancers and more about the possible benefits of vitamin D. Beyond that there wasn’t much to say.
. . .
The situation seemed very different in 1997, when the World Cancer Research Fund and the American Institute for Cancer Research published a report, thick as a phone book, concluding that diets loaded with fruits and vegetables might reduce the overall incidence of cancer by more than 20 percent.
After reviewing more than 4,000 studies, the authors were persuaded that green vegetables helped ward off lung and stomach cancer. Colon and thyroid cancer might be avoided with broccoli, cabbage and brussels sprouts. Onions, tomatoes, garlic, carrots and citrus fruits all seemed to play important roles.
In 2007, a major follow-up all but reversed the findings. While some kinds of produce might have subtle benefits, the authors concluded, “in no case now is the evidence of protection judged to be convincing.”
The reason for the change was more thorough epidemiology. The earlier studies tended to be “retrospective,” relying on people to remember dietary details from the distant past. These results were often upended by “prospective” protocols, in which the health of large populations was followed in real time.
The hypothesis that fatty foods are a direct cause of cancer has also been crumbling, along with the case for eating more fiber. The idea that red meat causes colon cancer is shrouded in ambiguity. Two meta-analyses published in 2011 reached conflicting conclusions — one finding a small effect and the other no clear link at all.