Saturday, October 2, 2010

What's a PPT? Part 1

This gent is funny but a bit of a tough read.  BLUF:  The fiber myth is proved mythical.

"The Polyp Prevention Trial, PPT. For those of us who have forgotten, this quote from the abstract sums up PPT:
"This study failed to show any effect of a low-fat, high-fiber, high-fruit and -vegetable eating pattern on adenoma recurrence even with 8 years of follow-up."
"Now, would anyone like to guess how much the PPT cost? I've no idea, but I guess it cost enough that you are not going to accept a result like that after spending all of those tax dollars (thank goodness it wasn't pounds sterling, it's bad enough funding the FSA on this side of the Pond). So there is now an on-going avalanche of subgroup analysis papers flooding out from PPT, many of which are utterly hysterical. Some actually show, by accident, the injury done to many of the people in the intervention arm of the study. From these new papers you would NEVER guess the main trial primary end point was an utter destruction of the hypothesis that flatulence is good for you.
"Let's start with that lovely sub group who ate all the dry beans. Upping your beans by 370% appeared to drop your risk for adenoma recurrence to an OR of 0.35 in the intervention arm. This is music to the fibre-ophile ear. The effect is massive. It really should show in observational studies if it is real. It doesn't.
"That last sub group analysis is particularly interesting once you get hold of the full text (many thanks Anna). It only looks at the control arm, so it's observational in nature. They blood sampled folks at the start of the study then counted polyps after four years on whatever shade of the SAD happened to be chosen by people who have had a polyp removed but no diet advice given (ie the lucky ones).
"What is topical to me at the moment is that homocysteine (HCy) correlation with polyp recurrence. HCy at enrolment is a very good predictor of polyp recurrence in this group of untutored polyp formers over the next 4 years.
"The suggestion, by the authors, is that reducing HCy will reduce adenoma recurrence. Really, someone should test this hypothesis. Maybe a trial increasing fruit, vegetables and fibre should be done to see if these miracle foods will reduce adenoma formation over a four or even eight year period?
"Oh, it's been done has it? Ah yes, that's where this data trawl has come from! I remember, yes, that's it, eight years of fruit and fibre does bugger all to prevent polyp recurrence. Silly of me to forget. There was an intervention arm to PPT!"

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