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• Methodological considerations of a systematic review and meta-analysis: dietary carbohydrate restriction in patients with type 2 diabetes
  Rosemary E Huntriss, Malcolm Campbell
  Published on: 8 June 2017

• Published on: 8 June 2017

  Methodological considerations of a systematic review and meta-analysis: dietary carbohydrate restriction in patients with type 2 diabetes

  • Rosemary E Huntriss, Specialist Diabetes Dietitian Bradford Teaching Hospitals NHS Foundation Trust
  • Other Contributors:
    • Malcolm Campbell, Lecturer in Statistics

  Thank you to the authors for addressing a relevant and interesting area of research (Snorgaard et al., 2017).

  The review was well planned, but the methodology lacks detail that enables the reader to understand the processes involved in the completion of the meta-analysis and some study limitations were not described.

  Please could the authors clarify why the meta-analyses use both mean change from baseline and mean final value in the same meta-analysis (see Figure 2 and Figure 3 where the lower means indicate change from baseline and the higher means indicate unadjusted final values)? Also, could it be clarified why the selected arms from the three-arm trials were chosen over the arms that were omitted? Although the population, intervention and outcomes were defined in the methodology, the comparator was not.

  Furthermore, when using the mean final HbA1c value in the meta-analyses, papers such as Krebs et al. (2012) and Guldbrand et al. (2012) have higher baseline HbA1cs in the lower-carbohydrate group, which was not mentioned in the paper, nor mentioned as a limitation to the meta-analysis. Guldbrand et al. (2012) demonstrate that HbA1c remained the same at two years (the time point the authors refer to) in the lower-carbohydrate arm but increased in the comparator arm by 0.2%. Therefore the low-carbohydrate arm was the superior intervention; however, the forest plot (Figure 3) suggests that the control intervention was slightly but not significant...

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  Thank you to the authors for addressing a relevant and interesting area of research (Snorgaard et al., 2017).

  The review was well planned, but the methodology lacks detail that enables the reader to understand the processes involved in the completion of the meta-analysis and some study limitations were not described.

  Please could the authors clarify why the meta-analyses use both mean change from baseline and mean final value in the same meta-analysis (see Figure 2 and Figure 3 where the lower means indicate change from baseline and the higher means indicate unadjusted final values)? Also, could it be clarified why the selected arms from the three-arm trials were chosen over the arms that were omitted? Although the population, intervention and outcomes were defined in the methodology, the comparator was not.

  Furthermore, when using the mean final HbA1c value in the meta-analyses, papers such as Krebs et al. (2012) and Guldbrand et al. (2012) have higher baseline HbA1cs in the lower-carbohydrate group, which was not mentioned in the paper, nor mentioned as a limitation to the meta-analysis. Guldbrand et al. (2012) demonstrate that HbA1c remained the same at two years (the time point the authors refer to) in the lower-carbohydrate arm but increased in the comparator arm by 0.2%. Therefore the low-carbohydrate arm was the superior intervention; however, the forest plot (Figure 3) suggests that the control intervention was slightly but not significantly superior. The paper by Krebs et al. (2012) concluded that both groups had an increase in HbA1c of 0.1% at trial end suggesting no superiority of either intervention; however, again the forest plot (Figure 3) indicates that the effect size was slightly but not significantly in favour of the control group. It appears that the inclusion of these data in their current form may limit the reliability of the meta-analysis seen in Figure 3. Could the authors or editor please comment on this.

  With many thanks.

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  Conflict of Interest:
  None declared.

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