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Can plants stop prostate cancer progressing?

Executive Summary

* Recent headlines claimed that a diet rich in fruit, vegetables and nuts can HALVE odds of prostate cancer spreading.

* The claim was based on a population study (association, not causation), which used data for just over 2,000 US men diagnosed with prostate cancer.

* The study used the Harvard created concept of a Plant-based Diet Index (PDI) and a Healthful Plant-based Diet Index (hPDI). The PDI rated all plant foods as good and animal foods as bad. The hPDI rated 'good' plants as good and ‘bad’ plants and animal foods as bad.

* The study examined prostate cancer progression and mortality. Nothing was claimed for mortality. There was essentially one claim for cancer progression (the headline claim) for the PDI review. Nothing else was found. Notably nothing was found for the hPDI.

* The paper was fatally flawed:

- The lowest BMI group was claimed to have at least 40% higher calorie intake than the highest BMI group. The Food Frequency Questionnaire clearly could not be relied upon.

- There was a seven-fold difference in diabetes in the comparator groups, which was not adjusted for.

- The only difference between the PDI and hPDI was 'bad' plants. Notwithstanding that the FFQ rendered the whole study void, if the PDI found one result and the hPDI found none, this must have been the result of 'bad' plants. No headlines about 'good' plants can therefore be made.

 

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