December 5, 2016

We say ‘nuts’ to news release claiming nuts cut risk of many diseases

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association ≠ causation

Gary Schwitzer is publisher of HealthNewsReview.org. He tweets as @garyschwitzer and/or by using our project handle @HealthNewsRevu.

“Nuts” – that was the one word that a US Army officer used to respond to a Nazi call for surrender of the encircled American troops near Bastogne, Belgium in December 1944.

72 years later, “Nuts” could be my one word response to a news release from Imperial College London that promised, “A handful of nuts a day cuts the risk of a wide range of diseases.”

And we won’t surrender, either, despite the relentless attack of PR news releases and on news stories that conflate association with causation. We’ll keep shining a light on this problem.

association-and-causation_1 There are many ways to say this, but remember whichever works best for you.

Association ≠ Causation.

Correlation ≠ Causation.

Or, as our graphic states: Association between two things does not mean one thing caused the other to happen.

The Imperial College news release states:

A large analysis of current research shows that people who eat at least 20g of nuts a day have a lower risk of heart disease, cancer and other diseases.

The analysis of all current studies on nut consumption and disease risk has revealed that 20g a day – equivalent to a handful – can cut people’s risk of coronary heart disease by nearly 30 percent, their risk of cancer by 15 percent, and their risk of premature death by 22 percent.

An average of at least 20g of nut consumption was also associated with a reduced risk of dying from respiratory disease by about a half, and diabetes by nearly 40 percent, although the researchers note that there is less data about these diseases in relation to nut consumption.

I added the bold, italicized, underlined emphasis. The “can cut risk” statement is causal and should not be used. The “was associated with” statement is accurate, because all that was found was a statistical association found by analysis of 29 studies of more than 800,000 people. It wasn’t a true experiment. There was no intervention. It was an observation of what happened to people over time. The study can be found online.

The news release didn’t have one word about the limitations of the evidence – nothing such as this reminder in the published journal manuscript:

“results from observational studies alone cannot be used to draw conclusions with regards to whether the observed associations are causal”

Let me emphasize: there is a growing body of evidence about the potential benefits of people eating nuts and this large meta-analysis adds to that body of evidence.

But that is no reason to inflate the findings as if they showed something they did not – that nut consumption caused fewer cases of heart disease.

We’ve written about observational studies about nut consumption before. Examples:

https://www.healthnewsreview.org/2013/11/nuts-and-death-journal-video-explanation/

https://www.healthnewsreview.org/review/walnuts-for-diabetes/

Our longstanding primer on the language used to describe observational studies may be helpful for broader understanding.

It’s too late to help these already-published news stories:

New York Times: A Handful of Nuts Is Good For Your Health

TIME: Eating a Handful of Nuts May Prevent Major Diseases

Voice of America: Daily Handful of Nuts Reduces Disease Risk: Study

Telegraph: A handful of nuts a day could slash risk of heart disease and cancer

Medical News Today:Daily handful of nuts slashes the risk of disease and death

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