Do whole grains prevent heart disease?

23 Sep 2023 | Data is not evidence

Study: Whole Grain Consumption Lowers Death Risk

That’s the title of an article in HCP Live, a clinical news and information portal for doctors. It’s consistent with what everyone tells you about the benefits of whole grains. But while some superfoods are peddled out of thin air, this one seems to be backed up by evidence. And not just any evidence, but a study published in the prestigious Journal of the American Medical Association network.

The researchers had a wealth of data. They studied the dietary habits of 74,341 women and 43,744 men over decades. In total, they had 2,727,006 person-years and 26,920 deaths. The conclusion was clear: people who ate more whole grains lived longer. In the authors’ words: “Every serving of whole grain (28 grams daily) was associated with a 5% lower total mortality or a 9% lower cardiovascular disease (CVD) mortality.”

But that’s only a correlation; it’s not causation. People who choose to eat whole grains might differ from those that don’t in many other ways. Perhaps they’re wealthier, because whole grains are more expensive than fast food, and their wealth gives them better housing, superior healthcare, and an easier life — all of which help them live longer. Or, since whole grains have a healthy allure, devotees of clean living are more likely to consume them, and its their clean living that boosts their health. This is an example of why data is not evidence: it may not be conclusive if it’s consistent with alternative explanations.

This problem extends to any study examining a voluntary choice, because people who make that choice might be special in other dimensions. Instagram influencers endorse weight loss supplements — but people who choose to buy a supplement are likely taking other actions to shed pounds, such as exercising more, eating better and drinking less. Those actions could be causing the weight loss, not the supplement. Motivational speakers reel out testimonials from devotees whose lives were changed after attending their seminars — but those willing to shell out hundreds of dollars and drive for six hours to hear a talk are likely taking other steps to better themselves. Those actions could be causing the turnaround, not the guru’s five-point plan.

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