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• Re:Nutty conclusion in walnut study
  Valentine Y. Njike
  Published on: 6 April 2016
• Nutty conclusion in walnut study
  Stephen L. Black
  Published on: 6 April 2016

• Published on: 6 April 2016

  Re:Nutty conclusion in walnut study

  • Valentine Y. Njike, Assistant Director, Research and Evaluation
  • Other Contributors:
    • Rockiy Ayettey, Paul Petraro, Judith A. Treu, David L. Katz

  We appreciate the attention to our manuscript[1].

  We will start by emphasizing that we cannot control what has been written in the media about this study. We will therefore limit our response to the reviewer's comments that directly pertain to our manuscript.

  The results of this study are clearly enumerated in the paper, with the supporting data shown in every instance[1]. We distinguish explicitly be...

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  We appreciate the attention to our manuscript[1].

  We will start by emphasizing that we cannot control what has been written in the media about this study. We will therefore limit our response to the reviewer's comments that directly pertain to our manuscript.

  The results of this study are clearly enumerated in the paper, with the supporting data shown in every instance[1]. We distinguish explicitly between between- group and within-group effects, noting that the between-group effects are primary. In studies that cannot be blinded, however, there are well-known Hawthorne effects, which can attenuate statistical power in unpredictable ways. Thus, isolated within- group effects, though secondary, are nonetheless relevant and of interest, and may speak to issues that warrant reinvestigation in trials with greater statistical power.

  While we considered Hawthorne effects to the greatest extent possible in our study design, it is very difficult to anticipate their magnitude in any given context. We were thus left to conjecture about such effects in the interpretation of our data.

  Interpreting data from different perspectives, rather than relying on a single approach, helps to overcome Hawthorne and other potential effects that may obscure meaningful associations. This, of course, is uniquely important in lifestyle interventions that cannot be fully blinded. Presenting only between-group effects would provide a stunted view, and perhaps a misrepresentation of our findings. This is particularly true given the relatively small sample size. We do not mistake our secondary outcomes for primary, and nor should our readers. We do, however, think that these findings warrant readers' attention. We clearly note the basis for our data interpretation and the relevant limitations in our manuscript.

  References

  1 Njike VY, Ayettey R, Petraro P, Treu JA, Katz DL. Walnut ingestion in adults at risk for diabetes: effects on body composition, diet quality, and cardiac risk measures. BMJ Open Diabetes Res Care. 2015 Oct 19;3(1):e000115. doi: 10.1136/bmjdrc-2015-000115. eCollection 2015.

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  Conflict of Interest:
  None declared.

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• Published on: 6 April 2016

  Nutty conclusion in walnut study

  • Stephen L. Black, Professor emeritus

  Nutty conclusion in walnut study

  This study purports to show that eating walnuts lowers cholesterol level, a claim enthusiastically and uncritically repeated in the media (e.g."A handful of walnuts a day may help lower cholesterol:study", CTV News, November 25, 2015). Unfortunately, the claim is spurious, as the published data show no such effect.

  The study is well-controlled in including a randomized control group...

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  Nutty conclusion in walnut study

  This study purports to show that eating walnuts lowers cholesterol level, a claim enthusiastically and uncritically repeated in the media (e.g."A handful of walnuts a day may help lower cholesterol:study", CTV News, November 25, 2015). Unfortunately, the claim is spurious, as the published data show no such effect.

  The study is well-controlled in including a randomized control group of subjects not eating walnuts. However, the results fail to show a significant difference in cholesterol level between this control group and the group which did eat the nuts. Instead of focusing on this central comparison of the study, the authors chose instead to emphasize a significant within-group decline in cholesterol level over the experiment in the group eating nuts. At the same time they ignored the fact that cholesterol also significantly declined in the group not eating nuts.

  In their own words, they stated "When compared with the walnut-excluded phase, the walnut-included diet showed no significant improvement [in cholesterol]. Yet in their highlighted "Key message", they claim the opposite: "The inclusion of walnuts in habitual diet...improved cholesterol". A similar claim appears in their press release.

  Given the decline in both groups, logic requires that if they are going to claim that eating walnuts lowers cholesterol, they must also claim that not eating walnuts lowers cholesterol. To avoid this nonsensical pair of conclusions, the authors should have refrained from a selective, misleading, and contradictory interpretation of their data and told us instead only that they failed to show that eating walnuts lowers cholesterol.

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  Conflict of Interest:
  None declared.

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