Anyone paying attention to nutrition science in recent years is aware of how dramatically our eating guidelines have been turned upside-down. Butter, saturated fats, eggs, salt and red meat: in recent years all of these ingredients have enjoyed major reevaluations. What pillar of received nutrition wisdom will be toppled next?
It could be fiber. At the vanguard of the low-carbohydrate movement, experts have begun to question fiber’s role in a healthy diet. Is fiber necessary? Is it even good for you? The very questions may be startling, as most of us have long taken fiber’s importance in a balanced diet for granted.
Doctors and nutritionists commonly credit fiber with many health benefits: improved bowel health, lower cholesterol and blood sugar, weight loss, and reduced risk of heart disease and cancer. What’s not to like? And if anything, the case for fiber seems to be getting stronger. It’s only in recent years that scientists have realized that fiber has a major effect on the composition of the gut microbiome, possibly the mechanism by which a substance which passes through the body undigested can promote good health.
The Case Against Fiber
Prominent critics of dietary fiber recommendations – including doctors Zoe Harcombe and Paul Mason and biochemical engineer Ivor Cummins – argue that the evidence in favor of fiber is both meager and unreliable. While many studies have linked fiber consumption to better health outcomes, the reported change in absolute risk is usually quite small, and the quality of the data itself is usually poor. Significant randomized controlled trials on dietary fiber intake are basically nonexistent, forcing experts to rely largely on observational studies, which are always hampered by significant limitations. One particular flaw is that people who eat more fiber tend to make healthier decisions in general, a confounding factor that is almost impossible to account for. Ultimately, as an article in the Canadian Journal of Gastroenterology concluded, “current evidence does not justify routine recommendations of fibre supplementation.”
A Brief History of the Fiber Man
So how did we get here? It’s instructive to look at the origin of the “dietary fiber hypothesis.” In a nutshell, modern fiber theory was developed around 1970, most prominently by one Dr. Denis Burkitt. Burkitt spent some years as a surgeon in Africa, where he noted the high amount of fiber in the local diet as well as the comparative absence of obesity, cardiovascular disease, diabetes, and other major and minor maladies common to Western society. He proposed that all of these issues had a simple common cause: low dietary fiber intake. He wrote a book titled Don’t Forget Fibre in your Diet, and became popularly known as the Fiber Man.
Burkitt’s hypothesis was massively influential, but in hindsight it’s not terribly convincing. There’s no good reason to assume that so many complex and apparently unrelated diseases – from clogged arteries, colorectal cancer and appendicitis to tooth decay and varicose veins – should share a single cause. Burkitt, for that matter, “did not really understand what fibre was,” and nobody has yet validated his grand vision of fiber as a solution to so many modern diseases. And yet all this tenuous guesswork created the foundation for the medical establishment’s endorsement of fiber’s importance in our diet.
Why Fiber Seems Healthy
When examined closely, we still can’t really be sure what fiber itself does. The National Academy of Sciences has stated that “there is no conclusive evidence that it is dietary fiber rather than the other components of vegetables, fruits, and cereal products” that confer apparent health benefits. Even the controversial vegan doctor Michael Greger has also concluded that Burkitt erred when he focused so narrowly on fiber by totally ignoring other components of whole plant foods.
It is possible that fiber mostly appears to be healthy because it serves as a proxy for the inclusion of healthful whole foods in diet, and/or because its inclusion necessarily excludes the refined starches that are so harmful. This will be a familiar story to ASweetLife readers, who already know that the hyper-processed carbohydrates of the Standard American Diet are bad news.
As it happens, a friend of Burkitt’s was working on the same problem at the same time. Dr. Thomas Cleave agreed that diet was the likely cause of heart disease, diabetes, tooth decay, and so on. Burkitt and Cleave agreed that refined grains were at the very heart of the issue. But Cleave, instead of blaming the removal of fiber, instead blamed the proliferation of highly refined carbohydrates, particularly sugar and white flour. History remembers the Fibre Man, but perhaps the time is ripe for a reevaluation of Cleave’s importance in this story.
So, Do You Need More Fiber on a Low-Carb Diet?
There is no unanimity among low-carb advocates regarding fiber’s importance. Tim Noakes, the dean of low-carb diets in South Africa, recommends a diet that is high in fiber. Dr. Ted Naiman, who recommends a very high protein diet akin to Dr. Richard Bernstein’s prescription for people with diabetes, identifies fiber as an important part of his diet, chiefly for its effect on satiety.
Doctors Stephen Phinney and Jeff Volek have a more subtle take. They do not dispute the importance of dietary fiber for those consuming a mainstream high-carb diet, but argue that it is less important in the context of a ketogenic diet. They also stress that it is easy to eat plenty of fiber from vegetables, nuts, and fruits, if one were so inclined.
And then there are the hardliners…
Carbs are non-essential; fiber only found in carbs. Therefore fiber also non-essential. A simple nutritional fact
— Dr Zoe Harcombe, PhD (@zoeharcombe) November 12, 2016
Fiber is largely a proxy for "lack of processing" – in and of itself it adds little to the party. This is an important point. Hugely important. @gerdosi
— Ivor Cummins (@FatEmperor) June 23, 2018
Naturally, prominent fiber nay-sayers are often associated with diets that are very low in fiber, particularly the increasingly trendy all-meat diet variously called “zero-carb” or “carnivore.” We considered the health and efficacy of the all-meat diet a year ago, and concluded that the lack of study combined with its relative novelty made it difficult to judge as a strategy for diabetes. But at least we can be confident that any diet with virtually zero carbohydrates won’t unduly spike one’s blood sugar, and that alone makes it worth paying attention to.
While fiber’s position as a central dietary component may be debatable, at the very least, we can all agree that fiber is good for digestive regularity, right? In something of a shocker, even this closely-held conventional wisdom also appears to be dubious. Here’s a whopper of a study where patients complaining of constipation were put on high-, reduced-, and zero-fiber diets. The zero-fiber diet relieved all symptoms and quickly restored regular, comfortable bowel movements. The high-fiber diet, by contrast, made everything worse.
For now, the long-term impact of fiber consumption has to be considered an unknown. As for the short-term impact, your mileage may vary. In surveys of the low-carb online community, we found anecdotal evidence both for and against fiber as a useful antidote to constipation and other belly troubles. With judicious consumption of high-fiber ingredients such as cauliflower, avocado, chia seeds, nuts, berries, and coconut, it’s not difficult to meet recommended amounts even while observing a very low-carb diet.