On Fiber

I am reading the most amazing book, Good Calories Bad Calories by Gary Taubes.  I've had this book for a while, but haven't had the time to read it.  It is long and scientifically dense, and it challenges just about everything I thought I knew about nutrition. He has taken aim at the lipid hypothesis, salt intake, calories in and calories out, but I was floored when I read chapter 7 in the book on fiber.

In the early 1970's, a missionary surgeon named Denis Burkitt, proposed that fiber, the indigestible carbohydrate roughage, was an absolutely necessary element to a healthy diet.  He claimed the absence of fiber in the diet was the reason behind diseases of civilization, those diseases that appeared wherever the Western diet, which was largely devoid of fiber, was consumed (e.g., diabetes, heart disease, high blood pressure, cavities, appendicitis, cancer, etc.).  Burkitt publised his fiber hypothesis in the British journal The Lancet in 1972 and, with missionary zeal (Taubes describes it as "messianic" zeal), aggressively promoted the hypothesis. The media jumped on the fiber band wagon, and the belief that fiber would prevent colon cancer and other diseases of civilization became conventional wisdom.

There's just one small problem with this hypothesis: there is no empirical evidence to back up the fiber hypothesis.  Says Taubes, "Over the last quarter-century, Burkitt's fiber hypothesis has become yet another example of Francis Bacon's dictum of "wishful science"--there has been a steady accumulation of evidence refuting the notion that a fiber-deficient diet causes colon cancer, polyps, or diverticulitis, let alone any other disease of civilization" (p. 132).  Two Harvard studies, one of 49,000 male health professionals and another of 89,000 female nurses confirmed that increasing the fiber in the diet by eating more whole grains, fruits, and vegetables had no beneficial effect on colon cancer, nor did it prevent heart disease, breast cancer, or other diseases of civilization.  A half dozen other, smaller studies also came to the same conclusions (see the notes for chapter 7 for references to the studies; I am traveling through Scotland as I write this and don't have the time to search online for the references). Gradually, a quarter century of studies has failed to support Burkitt's hypothesis, yet the belief that fiber is healthy remains alive.  Apparently, it is just another load of CWOPO. Taubes does concede, however, that eating fiber helps with constipation.

Research Update

Three interesting articles I found on the web.

This article compares a high protein diet with a high carb, high fiber diet and concludes the high protein diet was significantly better in helping women lose fat and lower blood pressure than the high carb, high fiber diet.  Note that the "high protein diet" was a low fat diet and relatively high in carbs:  30% protein, 40% carbs, 30% fat.  The high carb diet was 50% carbs (with more than 35 grams of dietary fiber), 20% protein and 30% fat.  So it was not really a "low carb" versus a high carb diet.  Still, it is interesting to note that despite all of the pro fiber voices out there, a diet lower in fiber and higher in protein still beat the high carb, high fiber diet.  I used to eat a lot of legumes (black, red, kidney, Great Northern, or garbanzo beans), because they were high in fiber.  But I have since learned that they are also very high in carbs (35 to 121 grams of carbs per one cup serving depending on the type of legume).  So the results of this study are not surprising.

Another article that is not really related to low carb diets suggests that extra weight at middle age leads to a greater likelihood of dementia when you are older.

Finally, a growing body of research confirms that the artificial sweetener Stevia can be used with confidence.  It has been in use in Europe for a while now.  Stevia is a naturally occurring sweetener found in herbs grown in Paraguay and Brazil.   Stevia is sold in the U.S. under the brand names Truvia and PureVia.

Fruits and Vegetables

I keep learning that I have been misled in life, nutritionally speaking.  Are fruits and vegetables the wonder foods they are made out to be?  I do eat veggies, especially leafy and green vegetables, and occasionally I eat raspberries.  But three recent studies have opened my eyes to the so-called benefits of a diet high in fruits and vegetables.

One study concluded that a diet high in fruits, vegetables and grains (and low in fat) did not significantly reduce the risks of coronary heart disease, stroke, or cardiovascular disease in post menopausal women over the eight years of the study.

Another study concluded that a low fat, high fiber diet with a lot of fruits and vegetables had no significant effects staving off a second bout of breast cancer in women who already beaten breast cancer once.  This was a 7.3 year long study.

A third study failed to find any beneficial effects of a low fat, high fiber, high fruits and vegetables diet on recurrence of bowel cancer in victims who had already suffered from this cancer, even after eight years.

So, where are the studies that show beneficial effects of a low fat, high fiber, high fruit and vegetable diet?  I haven't yet found any.  That doesn't mean they don't exist, but it is quite easy to find studies that show no beneficial effects and I have not had such an easy time locating the studies with empirical results demonstrating the benefits of a diet high in fruits and vegetables (and low in fat).