by Marion Nestle
Mar 13 2023

Industry-funded study of the week: Walnuts

I always enjoy the Headline vs Study section of the newsletter, Obesity and Energetics Offerings.

I particularly like this one because the headline says one thing but the study says another, and the authors put a positive spin on the results (interpretation bias).

The study: The Effects of Walnuts and Academic Stress on Mental Health, General Well-Being and the Gut Microbiota in a Sample of University Students: A Randomised Clinical Trial.  Nutrients 202214(22), 4776;

Rationale: Poorer mental health is common in undergraduate students due to academic stress. An interplay between stress and diet exists, with stress influencing food choices.

Results: Academic stress was associated with lower gut microbial diversity in females, which was improved by walnut consumption.  The effects of academic stress or walnut consumption in male participants could not be established due to small numbers of participants. Thus, walnut consumption may have a protective effect against some of the negative impacts of academic stress, however sex-dependent mechanisms require further study.

Overall conclusion: While daily consumption of walnuts could not alleviate disturbances in mood, it had a protective effect against the negative impacts of academic stress on mental health…daily walnut consumption over 16 weeks was able to alleviate the negative effects of academic stress on the diversity of the gut microbiota in females, however the relevance of these changes to the biochemistry of chronic stressors such as academic stress requires further study.

Funding: This research was co-funded by the University of South Australia (UniSA) and the California Walnuts Board & Commission…Walnuts for the study participants were provided by the California Walnuts Board & Commission. ..We thank Walnuts Australia for providing walnuts to the control group (upon completion of the study)….

Conflicts of interest: The sponsors had no role in the design, execution, interpretation, or writing of the study. The authors declare no conflict of interest.

Comment: The study didn’t show much, despite the enormous amount of work that went into it.  This looks like an excellent example of interpretation bias—putting a positive spin on barely significant results.  Industry-funded research usuall gets interpreted positively and recipients of industry funding believe that it does not influence them or cause conflicted interests.  But much research says it does.  And then, of course, this is a study of the effects of one food, usually not eaten in large amounts (nuts are expensive!) in diets containing large numbers of other foods.  Attributing big health effects to any one food hardly ever makes sense.


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