A common nutrition meme is that fiber is fantastic for you and you should eat large quantities of it. However, that widespread belief may very well be false. It would seem that not only is it difficult for our bodies to extract the abundant nutrients within fibrous and mineral-dense whole grain foods, but these foods frequently have anti-nutrients that may make you even worse off by hurting absorption of nutrients in the other foods you are eating.
The study cited below doesn’t quite damn fiber; however, it does indicate that it’s not the panacea its claimed to be and individuals probably don’t need to up their fiber intakes.
Even though its a sidenote in his post, Stephan’s comments about polyphenols are worthy of follow-up research.
Finally, Stephan expounds upon fermentation as a means to up nutrient absorption. It seems to me that fermentation is the oldest food processing technique in human history — even as food rots a hungry hunter gatherer is still going to eat it!
Mainstream health authorities are constantly telling us to eat more fiber for health, particularly whole grains, fruit and vegetables. Yet the only clinical trial that has ever isolated the effect of eating a high-fiber diet on overall risk of death, the Diet and Reinfarction Trial, came up with this graph:
Oops! How embarrassing. At two years, the group that doubled its fiber intake had a 27% greater chance of dying and a 23% greater chance of having a heart attack. The extra fiber was coming from whole grains. I should say, out of fairness, that the result wasn’t quite statistically significant (p less than 0.05) at two years. But at the very least, this doesn’t support the idea that increasing fiber will extend your life. . . .
Chief among these is phytic acid, with smaller contributions from tannins (polyphenols) and oxalates. The paper makes a strong case that phytic acid is the main reason fiber prevents mineral absorption, rather than the insoluble fiber fraction. This notion was confirmed here.
As a little side note, polyphenols are those wonderful plant antioxidants that are one of the main justifications for the supposed health benefits of vegetables, tea, chocolate, fruits and antioxidant supplements. The problem is, they’re actually toxins. They reduce mineral absorption, and the antioxidant effect seen in human plasma after eating them is due largely to our own bodies secreting uric acid into the blood (a defense mechanism?), rather than the polyphenols themselves. The main antioxidants in blood are uric acid, vitamin C and vitamin E, with almost no direct contribution from polyphenols. I’m open to the idea that some polyphenols could be beneficial if someone can show me convincing data, but in any case they are not the panacea they’re made out to be. Thanks to Peter for cluing me in on this. . . .
A more effective method is to grind grains and soak them before cooking, which helps the phytase function more effectively, especially in gluten grains and buckwheat. The most effective method by far, and the method of choice among healthy traditional cultures around the world, is to soak, grind and ferment whole grains. This breaks down nearly all the phytic acid, making whole grains a good source of both minerals and vitamins.