This is why observational studies don't tell us much...

Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies

Our meta-analysis supports an inverse association between intake of dietary fibre, cereal fibre, and whole grains and risk of colorectal cancer, but we found no significant evidence for an association with intake of fibre from fruit, vegetables, or legumes.

Taking this analysis, especially considering the quality, or lack thereof, of the studies reviewed and making the statement that dietary fiber and whole grains prevent colorectal cancer is about as ridiculous as taking the above conclusion and saying fruits and vegetables don't help in cancer prevention.

These types of studies only tell us of an association; there's no arrow of cause. And, as always when we observe cause and effect relationships in manners such as this, we end up with confounders...which are other associations that may have contributed to the effect...

Higher intakes of dietary fibre and whole grain are typically associated with other health behaviours, such as higher intakes of calcium and folate; higher levels of physical activity; lower prevalence of smoking, overweight, or obesity; and lower intakes of alcohol and red and processed meat.

Confounders such as these, if not accounted for, can muddy the water and skew the results quite a bit. And the authors in question had this to say...

Many but not all of the studies adjusted for potential confounding factors, although not all potential confounders were adjusted for in every study.

This is a poor quality analysis. However, even if all of the studies in question had adjusted for confounders...there's still no arrow of causation in observational studies. (and there's quite a bit of error involved with food frequency questionnaire studies, which most of these were) And at the end of the day, none of this really matters because the analysis still only found...

weak inverse associations between dietary fibre or whole grain intake and risk of colorectal cancer

That's right. It's a weak association that was found. And yet the headlines are reading...

"High-fibre diet cuts bowel cancer risk, analysis of 25 studies finds"

"High-fibre diet cuts bowel cancer risk by a fifth"

"High fibre diets CAN reduce the risk of bowel cancer"

"High Fiber Diet Reduces Colorectal Cancer Risk"

"Colon Cancer Risk Lowered With High-Fiber Diet"

....go figure.

or worse - they are out and out lies!

tobaccoanalysis.blogspot.com...

So what kind of statistical analysis does it take to turn a 21 % increase in admissions for female heart attacks after a smoking ban is implemented into a 21 % decrease?

See for yourselves.

Tired of Control Freaks

I'm not a medic but I have learned to research whoever is funding a study before I evaluate it's worth to my lifestyle. Nothing yet, and I'm 44, has detracted from the nutritional advise I received in school....enjoy a varied diet.

I remember they touted red wine as being a healthy option for as long as....until some bright spark thought to look into what else the wine drinker may be purchasing in their weekly grocery shop. Along with that red wine was fish, wholemeal bread, fresh fruit and veg etc etc.