Many Food Studies Serve Up Only Big Portions of Fear

In support of holding the line on “too much information,” a study recently published by the American Journal of Clinical Nutrition showed how data devoid of context is often useless and sometimes misleading.

The study concerned the abundant amount of research associating certain foods with disease risk, and how bold claims so often make their way into the public consciousness. (See our blog, “TV Doctors: Good Entertainment, Bad Medicine.”)

The journal authors concluded that you’re better off ignoring most of these food findings than you are changing your life to accommodate them. As noted in the Washington Post, if you conduct a Google search with the terms “foods associated with cancer,” you get 196 million results, “including new studies … on salt, aspartame and high-carb diets.” In this case, as in so many, more is less.

Most of the food studies showed weak, even insignificant, links to cancer. In their survey, researchers Jonathan D. Schoenfeld and John P.A. Ioannidis analyzed 50 common ingredients from random recipes in a cookbook; 40 had been the subjects of studies associating the ingredient with the risk of cancer. Staples such as salt, pepper, eggs and coffee were nabbed in the net of often sketchy research, as well as more exotic fare such as lobster, rum and mace (a spice).

Nearly 4 in 10 ingredients were deemed to increase the risk, 3 in 10 registered a decreased risk and nearly 1 in 4 showed no clear evidence either way. But the vast majority of the studies-8 in 10-showed really weak associations between the specific ingredient and cancer risk.

And, tellingly, the more statistically significant results showed up only in the abstracts of research studies, rather than in the meta data, where statistically insignificant results were more likely to appear. Abstracts summarize the results of a single study. Meta analysis is more meaningful because it’s more thorough; it crunches the numbers of different studies to contrast and compare them with the goal of identifying patterns among a body of study results. It’s like having a tiny bite of a complicated stew versus eating a whole bowl-you don’t get a sense of the whole meal by sampling just one ingredient.

As Schoenfeld and Ioannidis wrote, “Associations with cancer risk or benefits have been claimed for most food ingredients. Many single studies highlight implausibly large effects, even though evidence is weak. Effect sizes shrink in meta-analyses.”

If you want to reduce your risk of cancer, cardiovascular disease, diabetes and other disorders, you probably know how to begin: limit fat, sugar and alcohol, eat whole grains, fruits and vegetables and drink water. People with certain individual risks might want to limit their intake of salt, avoid gluten (a protein found in wheat and some other grains) and make other dietary adjustments as indicated by blood tests and other objective factors. But to revise your eating habits because a cute doctor on a talk show is excited about one recent study is to fall victim to fashion, not science.

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