Fiber: A Bran New Study has Back-end Results that are Hard to Digest. A new study from UNC Medical School questions long-standing beliefs about fiber in our diets.
“Heart Healthy Whole Grains”… Or Are They?
Of the many “truisms” in the world of natural health, hardly any is more universally accepted than the benefits of fiber. We hear of fiber’s benefits from nutritionists, medical doctors, gastroenterologists, health “gurus”, celebrity trainers, and many of our naturopathic colleagues.
Any mention of fiber in the media–on television, in magazines, on the radio–is generally about how we need to get more fiber in our diet and then usually followed by some lousy bathroom humor joke 🙂
The benefits attributed to fiber sound impressive. The Mayo Clinic states that fiber lowers the risk for diabetes and heart disease, lowers blood cholesterol levels, aids in weight loss, normalizes bowel movements, and helps the health and integrity of the intestines by lowering the risk for hemorrhoids and diverticulosis. (1)
There’s practically a public health movement to get us to eat more fiber.
Where are the highest sources of dietary fiber? Fruits, vegetables, whole grains, and legumes are the primary fiber-rich foods. Attention, however, seems to center upon grains and legumes. I’ve often observed the term “heart healthy whole grains” is so ubiquitous, I call it “hearthealthywholegrains”.
But is all of this true?
Intestinal Bacteria Like to Eat Your Fiber
First, we need to consider what fiber does inside our bodies. By definition, fiber is all of the parts of a plant that our body cannot digest or absorb. We can digest carbs, fats, and proteins. We can absorb their nutrients, along with their vitamins and minerals. But we don’t digest fiber. It is said that fiber passes through your digestive tract relatively intact, however, this doesn’t mean that it isn’t actively doing something.
Intestinal bacteria like to eat your fiber, and some intestinal flora can digest fiber. In return, short chain fatty acids are produced which we can then absorb and use for energy. In our opinion, this is a definite benefit of fiber. Short chain fatty acids (SCFAs), like butyrate, are great for our metabolism and immune systems.
Fiber also can have the effect of bulking stool and pulling water into the colon. This effect of fiber is why so many advise fiber to help with constipation and/or diarrhea. Fiber (say it with me now) keeps you regular.
These two effects–interacting with gut flora and pulling water into the colon–are well documented. The results, however, can be interpreted very, very differently.
The party line is that fiber helps to reduce pressure in the gut because we have more frequent and regular bowel movements. This is why fiber is so often recommended for issues like constipation and diverticulosis (an out-pouching of the colon that can run the risk of becoming infected or even rupturing).
Side Effects of Too Much Fiber
We’ve heard the following story so frequently: A person becomes constipated. They go online, read a book, talk to someone at the health food store, etc. They get the same advice: eat more fiber. At first, it seems to work. Soon thereafter, the problem comes back. They go to their doctor. Eat more fiber. The cycle repeats. They then go to their gastroenterologist. Eat more fiber. Cycle repeats.
Then they come and talk to us, and we tell them to eat LESS fiber. Huh? Wait, you’re naturopaths, right?
Constipation is NOT caused by a deficiency of fiber. Fiber sometimes temporarily “helps” by creating bigger stools which we are then compelled to get rid of. Our colon is only so big, and it doesn’t like to be stretched too far. Many years ago, a gastroenterology professor named Walter Alvarez did an experiment where he had his students insert enough cotton into their rectums to stretch the aperture of the colon. The results were not good. The students experienced headaches during this trial. (2)
Essentially, the same thing happens when we eat too much bulking fiber. The colon is chronically stretched which negatively impacts the nerve impulses to the gut. Over time, our brain-gut connection is altered. If the fiber is from grain sources, the result may include micro-tears along the lining of the wall of the gut. This produces a small, but persistent inflammation in the gut while potentially reducing nutrient absorption. (3)
As for the effect upon intestinal flora, if you have an imbalance between pathogenic gut bacteria and beneficial gut bacteria, your response to fiber may be room clearing. Many pathogenic bacteria ferment fibers and produce metabolic waste, such as methane. Gas, bloating, and cramping are all likely consequences of excessive fiber intake–especially in an environment of gut dysbiosis.
Studies That Make You Say “Hmmmm”
These concerns have just recently come to light due to a new study released by UNC Chapel Hill’s Medical School on January 23, 2012. The study measured data on 2,104 patients from 1998-2010. (4)
From the study (emphasis mine):
The study, conducted by researchers at the University of North Carolina at Chapel Hill School of Medicine, found that consuming a diet high in fiber raised, rather than lowered, the risk of developing diverticulosis. The findings also counter the commonly-held belief that constipation increases a person’s risk of the disease.
“Despite the significant morbidity and mortality of symptomatic diverticulosis, it looks like we may have been wrong, for decades, about why diverticula actually form,” said Anne Peery, MD, a fellow in the gastroenterology and hepatology division at UNC and the study’s lead researcher.
In fact, the study found those with the lowest fiber intake were 30 percent less likely to develop diverticula than those with the highest fiber intake.
The study also found constipation was not a risk factor and that having more frequent bowel movements actually increased a person’s risk. Compared to those with fewer than seven bowel movements per week, individuals with more than 15 bowel movements per week were 70 percent more likely to develop diverticulosis.
The study found no association between diverticulosis and physical inactivity, intake of fat, or intake of red meat. The disease’s causes remain unknown, but the researchers believe gut flora may play a role.
The results of this study should not be unexpected. A prior study in 2007 demonstrated nearly the same conclusion. (5)
The authors stated (emphasis mine):
“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. We urge clinicians to keep an open mind. While there are some benefits of a diet high in natural fiber, one must know the exact indications before recommending such a diet. Myths about fiber must be debunked and truth installed.”
This is exactly why we are doing our Naturopathic Myth Busters series!
What’s even more concerning about the knee-jerk recommendation of adding fiber to the diet is this graph correlating dietary fiber counseling and longevity. The following graph is from individuals post heart attack placed into two groups: One group was given advice to eat more dietary fiber, and the other group was not given advice to eat more fiber. (6)
Not exactly the results we’d like to see from “hearthealthywholegrains”…excess fiber was correlated to LESS longevity.
The Bottom Line
What’s our bottom line recommendation at Lewis Family Natural Health?
Fiber is something to get incidentally in the diet from eating plenty of fruits and vegetables.
If your digestive system tolerates grains and/or legumes well, then eating a moderate amount of fiber from these sources likely will have a net neutral effect on your health. On one hand, proliferating beneficial intestinal flora and increased SCFAs may be beneficial. From a practical standpoint, grains and legumes can be tasty, convenient, and economical. On the other hand, damage to the GI barrier is a potentially major problem.
Fibers from grains and legumes, however, should not be eaten for the sake of eating more fiber. Individuals who suspect they have an adverse reaction to gluten grains, other grains, or legumes may be better off sharply reducing or completely eliminating these fiber containing foods in their diet. Besides the fiber content, these foods have other substances that may be very detrimental to these individuals.
Excessive intake of fiber appears to be problematic, and we only see limited applications for fiber supplementation. Fiber consumption should not be a goal or a target, but rather a byproduct of eating a balanced diet.
- Mayo Clinic: http://www.mayoclinic.com/health/fiber/NU00033
- Ray Peat’s newsletter from May 2011, “Endotoxin, stress, depression: Serotonin, starches, fatty acids, and antidotes”
- Medical College of Georgia. “Scientists Learn More About How Roughage Keeps You ‘Regular’.” ScienceDaily, 23 Aug. 2006. Web. 27 Jan. 2012.
- University of North Carolina at Chapel Hill School of Medicine. “Diets high in fiber won’t protect against diverticulosis, study finds.” ScienceDaily, 23 Jan. 2012. Web. 27 Jan. 2012.
- Kok-Yang Tan, Francis Seow-Choen, World J Gastroenterol 2007 August 21; 13(31): 4161-4167
- M.L. Burr, M. Fehily, S. Rogers, E.Welsby, Sylvia King, and Susan Sandham, Diet and reinfarction trial (DART): design, recruitment, and compliance. Eur Heart J (1989) 10 (6): 558-567.