Let’s zero in on fiber for a second. I like to think of fiber as a Reality TV star: quite famous, but of questionable merit. While not as deleterious to our health as the low-fat paradigm, the whole EAT MORE FIBER thing is a bit misleading.
Fiber refers to indigestible carbohydrates found in the cell walls of plants. Fiber adds no real caloric or nutritional value to food, but it can serves as a bulking agent (“filling you up,” so to speak), regulate digestion, and feed gut flora. (This is why fiber may make you gassy – the little bacteria in your gut produce gas when they digest fiber). Fiber can be either soluble, meaning it dissolves in water, or insoluble, meaning it does not. Soluble fiber bulks up in your system, while insoluble fiber basically passes through unchanged.
Our dear friend Fiber first joined the popular crowd in the 1960s, when British surgeon Dennis Burkitt theorized that it protected against colon cancer. While studying lymphoma cancer affecting children in East Africa, Burkitt noticed that certain cancers prevalent in Western civilization were notably absent in poor, third world countries. He compared the indigenous population’s whole foods diet featuring fibrous fruit and vegetables, to the Western diet of refined flour and sugar, and concluded it was the lack of fiber in the refined diet which prevented colon cancer, rather than any other difference between the diets. (Perhaps the addition of refined sugar and carbohydrates?) Burkitt wrote a book on his findings (with no concrete supportive studies), and fiber became a legend.
As Gary Taubes says in Good Calories, Bad Calories “Better to say Don’t Forget Fibre in Your Diet, which was the title of Burkitt’s 1979 diet book, than to say ‘Don’t eat sugar, flour, and white rice, and drink less beer.”
Ok, so fiber’s rise to fame was based on an assumption, but surely studies later confirmed its health benefits, right?
Not so much.
A 2007 review of fiber studies until that point entitled “Primary dietary prevention: is the fiber story over?” noted the conflicting nature of such studies, concluding that the relation between fiber and colon cancer has not been adequately addressed, with further trials and research needed. That’s a lot of gray area for an EAT MORE FIBER mantra saturating a nation and fueling the sale of commercial products. More recently, a 2000 New England Journal of Medicine study evaluating the use of cereal bran fiber in 1429 patients concluded that “a dietary supplement of wheat-bran fiber does not protect against recurrent colorectal adenomas [precursors for colon cancer].” Shortly thereafter, a follow-up study in 2002 re-evaluated 1208 of the original patients just in case they weren’t actually eating enough fiber… and reached the same conclusion: “The results of this study show that neither fiber intake from a wheat bran supplement nor total fiber intake affects the recurrence of colorectal adenomas, thus lending further evidence to the body of literature indicating that consumption of a high-fiber diet, especially one rich in cereal fiber, does not reduce the risk of colorectal adenoma recurrence.”
And not only is fiber’s merits questionable, but excess fiber may even be detrimental. Back in 1979, a study found that, while a high animal protein (i.e.: meat) diet had no effect on colon cancer as suspected, adding fiber did increase calcium excretion despite an increase in calcium intake. 315 Besides calcium, excess fiber may also bind to other minerals such as magnesium and iron, making them less absorbable.
As noted in a 2003 Committee Commentary in the Journal of Pediatric Gastroenterology & Nutrition, potential risks of too much fiber in young children include maldigestion, malabsoprtion, and stunted growth 316. And while the commentary notes fiber may encourage insulin sensitivity and discourage childhood obesity, the reasoning is that adding fiber reduces “the excessive intakes of energy-dense, sweet, and fat-rich foods and drinks” associated with obesity and disease. Like Burkitt’s theory, fiber is once again heralded as “protective,” when in reality, it may be what is added which is causing the problem (i.e.: sugar and refined carbs).
A 2007 World Journal of Gastroenterology review nicely summarizes fiber’s controversial history, and concludes:
“A strong case cannot be made for a protective effect of dietary fiber against colorectal polyp or cancer. Neither has fiber been found to be useful in chronic constipation and irritable bowel syndrome. It is also not useful in the treatment of perianal conditions…The authors urge clinicians to keep an open mind about fiber…Furthermore, it is rare indeed to find a patient newly diagnosed with colorectal cancer who will not blame himself for not having taken more fiber. Recent studies have, however, not supported these benefits of fiber. Excessive fiber intake may in fact be harmful…Whilst it is not the intention of the authors to totally discourage fiber in the diet and the use of fiber supplements, there does not seem to be much use for fiber in colorectal diseases. We, however, want to emphasize that what we have all been made to believe about fiber needs a second look. We often choose to believe a lie, as a lie repeated often enough by enough people becomes accepted as the truth…Myths about fiber must be debunked and truth installed.”
I as well am not saying fiber in itself is necessarily a bad thing. I’m simply saying its benefits may be overhyped, especially in refined, processed food.
And of course, with all of this being said, if you’re still worried about getting enough fiber in a Paleo Diet, don’t worry. Calorie for calorie, the amount of fiber in green vegetables far outweighs that of grains. On a 100 calorie basis, bread contains around 1.5-3 grams of fiber, while green vegetable such as broccoli, spinach, and lettuce, contain 7-10 grams. Paleo foods high in fiber include green vegetables (broccoli, lettuce, brussels sprouts, etc.), squash, sweet potatoes, avocados, and fruits such as apples and berries.
So yes, Paleo gives you fiber. But perhaps you don’t need to stress about it anyways.