Are You Getting Enough Fiber?

This is a question often asked by doctors or other healthcare/fitness professionals. As a high-fiber intake has indeed been shown to have many health benefits, one of which is its ability to protect against type 2 diabetes.1 Although, conversely there are also benefits seen from a diet that is low in fiber, especially when it comes to gut health.2 This leads us to ask an important question, are the purported health benefits of fiber exclusively due to the Fiber content? I hope to answer this question and others you may have about fiber intake by the end of this article.

What Dietary Fiber Has Been Shown to Helpful for

Digestive Cancers

Digestive cancers are probably the most important issue involving fiber intake, as it’s the only area where eating a lower-fiber diet might be problematic. Several systematic reviews and meta-analyses have shown that increased fiber consumption protects against colorectal cancer.1 Fiber is also protective against stomach and esophageal cancer.3 Conversely, it is important to note, there is an equivalent amount of evidence showing fiber offers no benefits. As a clear majority of studies of studies show that neither cereal fiber nor whole-grain consumption protected against cancer.4 Also, no association between fiber intake and colorectal cancer was found in another study.5

Inflammatory Bowel Disease, Irritable Bowel Syndrome, Diabetes, Heart Disease, and Obesity

If we look at studies regarding fiber intake effect on other diseases we see that some show that it’s helpful and others show no benefits or even negative effects. Inflammatory bowel disease is one such example, as some studies have shown fiber to be helpful6 while others have shown no benefits and that a low-fiber diet has been shown to be an effective treatment.7 The same is true for irritable bowel syndrome (IBS), diabetes, heart disease, and obesity.

Is Fiber Alone Responsible for High-Fiber Diets Health Benefits

Likely Not

This leads us to an important consideration when talking about high-fiber diets. Often when people go on a high-fiber diet, they are eating a healthier diet in general as they are cutting out or down intake of processed foods, sugar-sweetened beverages, and other pro-inflammatory foods. They replace these foods with whole foods such as vegetables, fruits, and healthy meats and fats. Due to these changes many things happen, such as decreases in sugar intake, overall calorie intake, refined carbohydrate intake, food additives, and unhealthy processed fats (trans fats). There is also increases in protein intake, many nutrients and vitamins, healthy fats (mono-, poly-, and saturated-fats), and obviously in fiber (fruits, vegetables, grains). This leads to the conclusion, which is important to understand, that some or most of the health benefits of a higher-fiber diet appear to be due to other factors that accompany the diet itself, and not necessarily the fiber alone.

Fiber, Not Good for Those with SIBO

Another factor to consider is that fiber feeds bacteria in our microbiota, the ecosystem of bacteria in the gut. While this is not a problem for some it can be a problem for many others.8 This especially true for those with a condition known as small intestine bacteria overgrowth (SIBO). As the small intestine accounts for 56% of our entire intestinal tract, the colon represents roughly 20%. Further, the small intestine is responsible for 90% of caloric absorption and has a profound impact on our immune system.9 The small intestines normally harbors a relatively small number of bacteria. An excessive number of bacteria in the small intestines is associated with or may cause any major problems such as hypothyroidism, celiac disease, (gluten allergy), and IBS (gas, bloating, abdominal pain, constipation, and diarrhea).10

Could You have SIBO?

Why might this be relevant to you? Well, because those who eat a typical Western diet (most Americans) tend to have this overgrowth of bacteria in the small intestines. SIBO is just one example of why many approaches that feed bacteria growth, like a high-fiber diet, may not work well or even against many people.

Fiber, Good for Some & Bad for Others

When you consider all of this and you look at both sides of evidence, it’s clear that fiber can be beneficial for some and not so great or even harmful to others. Therefore, there is no easy or correct answer for everyone as fiber is not a black-and-white issue. Why do people react differently to higher or lower amounts of fiber? This is because of the same reason some people can’t eat gluten, do better eating a low-carb diet, or have problems eating certain foods – All of our guts are unique and they should be treated as such. You probably should not be eating a diet identical to that of a traditional culture in Africa, known as the Hadza tribe. Even though they have been shown to have healthier guts, microbiotas, and immune systems than people in the Western world.11 Why would we not want to follow their diet if they are healthier than us? Wouldn’t it be wise for everyone’s health to follow their example? No. It is not wise to replicate another culture’s diet or microbiota if you are not in that culture or population. There are a number of reasons for this and if you would like to find out what those are come back for next week’s article.

  1. https://www.ncbi.nlm.nih.gov/pubmed/26225683
  2. https://www.sciencedirect.com/science/article/pii/S0016508513004927
  3. https://www.ncbi.nlm.nih.gov/pubmed/27257283
  4. http://www.nejm.org/doi/full/10.1056/NEJM199901213400301
  5. https://www.ncbi.nlm.nih.gov/pubmed/26126709
  6. https://www.tandfonline.com/doi/abs/10.1080/10408398.2012.760515?journalCode=bfsn20
  7. https://cloudfront.escholarship.org/dist/prd/content/qt8d0680bq/qt8d0680bq.pdf
  8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4642427/
  9. https://www.ncbi.nlm.nih.gov/pubmed/16918875
  10. https://www.sciencedirect.com/science/article/pii/S0958166914001657
  11. https://www.nature.com/articles/ncomms4654.pdf