The fact that fiber aids in digestive health, heart health, and regulates blood sugar levels, to say nothing of potential benefits for weight control are becoming increasingly well known in the general public. In addition, these benefits are extremely well supported by scientific research, at least by the standards of nutrition science. There are many reasons for this, none of which I will explore here.
While Americans are finally increasing their much needed and long deficient fiber intake, there is a potential downside, and it helps to be well aware of it. That is what this post is about. Kind of like a public service announcement. If you are playing with fiber, without knowing what you are doing, you risk all kinds of problems you didn’t bargain for, from nutrient deficiencies to social stigma.
The reason for this is that not all “fiber” is created equal. In addition to quantity of dietary fiber intake, the quality of it matters a great deal. I’m not only talking about the crucial difference between soluble and insoluble fiber, but also the specific kind of fiber. As the thrust of this post is practical in nature, I don’t want it to devolve into a lecture on metabolic biochemistry, so we will stay clear of a discussion of saccharide polymers and the like.
The bottom line is that things are – as usual – more complicated than they seem.
Here is the take home message: Just because you cannot digest a particular kind of fiber does not necessarily mean that the bacteria in your gut can’t.
On the contrary.
There is no point to single out any one “bad” fiber, but one of them has recently become much more common than it used to be. Since the notion that fibers are good for you is becoming common sense, more and more foods tout their high fiber content. Predictably, the food industry is meeting this demand by simply adding fiber to processed foods. These days, this typically takes the form of Inulin, which is most commonly derived from chicory root extract. Worst offenders – at this point – are some popular “diet” bars, such as those by “Fiber One”, “Kashi” and “Kellog’s Fiber Plus”. As usual, it helps to read nutrition labels. The ingredients are listed in order of decreasing weight per serving.
There is nothing inherently wrong with chicory root or Inulin. As a prebiotic, it has quite a few documented health benefits. However, most people can tolerate it only in small quantities, even if they tolerate other kinds of fiber quite well. The reason for this is that Inulin provides a veritable feast for certain types of gut flora. Many people don’t have a well balanced gut flora to begin with. In the age of antibiotics, dysbiosis is common.
Feeding the wrong kind of bacteria can cause serious (no really, serious) amounts of gastro-intestinal upset, gas, explosive diarrhea and discomfort. This is obviously not good for nutrient absorption, either.
The actions of gut bacteria can have a profound effect on all bodily systems. What kind of effect that is depends on the kinds of bacteria you have in your gut as well as what you feed them.
In the spirit of keeping this practical, I will spare you links to the scientific literature on the topic and rather provide a connection to the best writeup of vox populi on this subject.
I strongly encourage you to read this. The comments are of particular interest.
As a psychologist, I cannot fail to notice that this topic seems to provoke a great deal of levity. This is quite curious, as I am not aware of any research on the issue.
Of course, few things are intrinsically good or bad. Valence usually depends on what one is trying to achieve. For instance, these can be quite effective for weight loss (given the double-whammy of low caloric content and likelihood of diarrhea), relieve constipation, make great gifts for bad neighbors and safely enrich the intestinal biome when introduced gradually and in small quantities. Perhaps, they could even be used to strengthen primal social bonds – one could imagine some kind of social gathering where all participants are required to consume large amounts of Inulin containing food.
In conclusion, there is such a thing as ingesting too much fiber. And – as always – it matters to know what one is doing. This is a responsibility that cannot be outsourced to agencies with a divergent incentive structure.
Update: When I wrote this, I would never have anticipated that it would turn out to be one of my most popular posts. I’ve also learned a lot from the comments. So if you had a lot of gas lately, particularly after starting to ingest Inulin, please do share you story below. It might be helpful to someone else.
PS: I understand that this may sound pretty outlandish to those outside the trade. I suggest you buy a box of the diet bars with chicory root extract as the primary ingredient (Fiber one will do), eat it, then relate the experience in the comments below.
Note: As pointed out above, there is plenty of evidence that the ingestion of fiber has positive health effects, including a reduction of all cause mortality. The message of this post is not that fiber is bad for you. Far from it. The message is that the source matters, as also pointed out in the research paper in the previous link. I personally make sure to eat at least 40 grams of fiber per day. However, I would like to emphasize that nutrition science is full of irreducible correlations. In other words, high fiber intake might just be a proxy for a certain kind of dietary style. If you eat something, you are less likely to eat something else. Hard to control for that, particularly in a questionnaire study. If you *do* want to increase fiber intake, most people have great results with Psyllium husks. 10 grams a day of that take care of most exhaust that is of a swampy/muddy consistency and generally allow to achieve – given adequate water supply – a consistent 4 on the Bristol stool scale. They do make a quite noticeable difference in achieving smooth outcomes (literally), to be sure. Don’t overdo that either, though. It tends to turn the whole thing into sort of a paste and can probably clog things up quite a bit. Everything in moderation and caveat lector.