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Randomised trial of coconut oil, olive oil or butter on blood lipids and other cardiovascular risk factors in healthy men and women
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  • Published on:
    Response to Sudry: Statistical Error
    • Kay-Tee Khaw, Emerita Professor University of Cambridge
    • Other Contributors:
      • Nita Forouhi, Professor
      • Stephen Sharp, Senior statistician

    Thank you for the comment.

    The P values shown in the column in Table 2 are for the ANOVA comparisons between the three intervention groups and, as the correspondent indicates for LDL-Cholesterol, this is shown as P<0.001. The P values described in the text are for the pairwise comparisons for which Table 2 does not show P values but only the 95% CI. Both sets of P values are correct.

    There is no error in our reporting, but in any case, the differences referred to are all conventionally highly statistically significant whether P<0.001 or P<0.0001 and do not alter the interpretation of results.

    Conflict of Interest:
    None declared.
  • Published on:
    statistical error

    Dear Authors, I'd like to raise a concern which I have in regards to the trial results. I believe there may be an error in your statistical display of the P-value for LDL-C for the butter group vs. the coconut oil & olive oil groups. Within the text, it is written that P <0.0001 when comparing LDL-C from butter vs. the coconut & olive oil groups (see Results - page 5). However, in Table 2 the P-value for the same outcome is <0.001 (see Table 2 - page 8). Please let me know if I am mistaken or if in fact there was a mistake made.

    Conflict of Interest:
    None declared.
  • Published on:
    Results may be Statistically Significant but are not Significant in Terms of Health Outcomes

    Note that the emphasis in this paper is on the amount of change after implementing the diets rather than the more important absolute values.

    Adding 50g of fat to a diet already high-fat diet is not a healthy dietary modification. All three diets were 36-37% fat (by energy) which is higher than the US average of 33%.

    The average total cholesterol for all diets at the start of the trial was 5.9-6.0 mmol/L – which is very high. The cholesterol was high at the start of the trial and was still high at the end. The Framingham Risk Assessment accumulates risk points at 160 mmol/dL (4.0 mmol/L) or greater for total cholesterol.

    Total cholesterol was raised for coconut oil (mean 0.22) and butter (mean 0.59). The average increase for olive oil was much less (mean 0.03). The standard deviation was higher for coconut oil and butter compared with olive oil (0.55, 0.59, 0.43).

    The baseline values for fasting glucose was 5.3-5.4 mmol/L. A frequently quoted reference range is 3.6-6.0 mmol/L although a reasonable desirable level is lower at 3.9-5.0 mmol/L. After 4 weeks, the fasting glucose was decreased an average of 0.05 mmol/L for coconut oil, raised 0.02 mmol/l for butter and decreased 0.06 mmol/L for olive oil. These are not a significant beneficial outcomes.

    Systolic blood pressure is also high. Optimal systolic blood pressure is less than 120. Coconut oil had a greater tendency to raise the systolic blood pressure compared to butter and olive oil....

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    Conflict of Interest:
    Author of book Low-carbohydrate Mania: The Fantasies, Delusions, and Myths
  • Published on:
    Response to Price et al: Randomised trial of coconut oil, olive oil or butter on blood lipids and other cardiovascular risk factors in healthy men and women
    • Kay-Tee Khaw, Professor University of Cambridge
    • Other Contributors:
      • Nita G Forouhi, Professor

    Dear Editors,
    Thank you for the comments from Jessica Price and colleagues. In response to the three points they raised:

    For pragmatic and scientific reasons this study did not have a control group as defined by a study group in whom no additional lipid was added/replaced in the diet. Interpretation of a comparison with such a control group would have been challenging in a free-living intervention that did not control the participants’ total energy intake which would have been substantially lower in the control group (by approximately 450 kcal/day based on 9 kcal per gram of fat in the intervention arms). However, we did include a highly relevant comparison group in the trial, taking extra virgin olive oil, as from the existing literature extra virgin olive oil is reported either to have no effect or to lower LDL-cholesterol, so we could also compare coconut oil with olive oil. The pre-specified primary outcome was a comparison of the effect of different fats/oils on changes in LDL-cholesterol. As can be seen in the results, coconut oil was not different from olive oil in terms of the changes in LDL-cholesterol. In addition, we also presented the absolute change in LDL-cholesterol concentrations following the interventions and the groups on coconut oil or olive oil showed no increase in LDL-cholesterol from baseline, if anything a non significant small decrease.

    As we state in the report, participants were free to consume the oil any w...

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    Conflict of Interest:
    None declared.
  • Published on:
    Response: Randomised trial of coconut oil, olive oil or butter on blood lipids and other cardiovascular risk factors in healthy men and women
    • Jessica Price, DPhil Student University of Oxford
    • Other Contributors:
      • Charlotte Albury, DPhil student
      • Kerstin Frie, DPhil student
      • Georgia Richards, DPhil student
      • Jack O’Sullivan, DPhil student

    We would like to congratulate the authors: the pragmatic trial design is novel and interesting, and may have provided a better estimate of the ‘real-life’ effectiveness of the intervention than a conventional RCT. Nevertheless, there are certain aspects of the paper that we wish to highlight. As the authors acknowledge, there are concerns about uncontrolled confounders. However, we would also like to raise the following 3 points of concern to consider:
    1. The study lacked a control group (where no additional lipid was added/replaced in the diet). This is problematic as the article’s conclusion suggests that the changes seen in LDL-C are an effect of extra virgin coconut oil, whereas it might instead be the impact of additional butter (and without a control group we are unable to assess the impact of coconut oil alone).
    2. The study is unclear about whether participants consumed the 50ml of coconut oil or olive oil as cold oils, or whether they cooked them before consumption. Multiple studies have suggested that hot (cooked) vegetable oil has a negative impact on blood lipids and metabolic profiles, increasing LDL-C levels, inflammatory markers and blood pressure (1). We would therefore welcome clarification of this point from the study authors.
    3. Longer follow up may be warranted to determine whether ongoing use of coconut oil would result in significant weight gain. This is of particular concern if coconut oil is added to the diet instead of replacing...

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    Conflict of Interest:
    None declared.