Fiber: More than just a poop-aid!


Fiber, it's the insignificant component of food we don’t digest, so it just goes right through us and all it really does is help us poop, right?

Wrong. Fiber is much more than a mere poop-aid.
Eating enough fiber is elemental to your health. Research shows that it aids weight loss and influences immune system regulation. Studies have shown that fiber can help prevent cardiovascular diseases, protect from diabetes and even lower the risk of certain cancers.

First things first, if the typical western diet is deprived of one major ingredient its fiber. Current dietary recommendations suggest a total daily dietary fiber intake of 25 to 30 grams [1].
A study looked at the daily fiber intake of US citizens and reported an average daily fiber intake of just 15 grams per day with a significantly lower fiber intake in obese participants [2].
There are basically two different types of fiber:

  • Soluble fiber can be dissolved in water and is fermented in the colon by our gut microorganisms.

  • Insoluble fiber does not dissolve in water and provides bulk to the stool.

SCFA Butyrate down-regulates the release of pro-inflammatory cytokines [5]

SCFA Butyrate down-regulates the release of pro-inflammatory cytokines [5]

Although we cannot digest fiber, our gut bacteria can digest it! We have developed a mutually beneficial relationship with the microorganisms living in our digestive system. The bacteria in out gut are extremely beneficial to our health if we treat them right.
Our gut inhabitants possess enzymes to digest and feed on the fiber we ingest, meaning that the fiber we eat promotes the growth of beneficial microorganisms in our intestines [3, 4].
But that is not all: The fiber-digesting microbes in-turn produce molecules called Short-Chain Fatty Acids, which been seen to suppress colon inflammation and carcinogenisis [5].

Research has shown us that nourishing and promoting a diverse gut community is critical to weight control, immune system regulation, fighting off bad bacteria and viruses, and even improving our mental functions and well-being. But this relationship can become toxic if we don't give the good bacteria what they need. If we don't give our good microbes what they need, they will starve and inflammation inducing "bad" bacteria will take over.

A diet deprived of fiber makes you sick

Bacterial Dysbiosis through high-fat diet (HFD) in combination with low-fiber intake [7]

Bacterial Dysbiosis through high-fat diet (HFD) in combination with low-fiber intake [7]

Two recent studies nicely demonstrate the negative effects of a diet deficient of fiber:
Dr. Gewitz and colleagues from the Georgia State University put mice on a low-fiber, high-fat diet to examine the health impacts of such a diet and found that the bacterial population crashed [6].

Change of Microbiome composition on WSD [7]

Change of Microbiome composition on WSD [7]

In another study, Dr. Bäckhed and his colleagues performed a similar experiment and switched mice from a normal diet to a low-fiber diet, which they called a Western Style Diet or WSD [7].
Dr. Bäckhed commented on his study by saying: “It [WSD] is basically what you’d get at McDonald's. A lot of lard, a lot of sugar and twenty percent protein”. They observed similar results to their colleagues from Georgia: Many beneficial bacteria species became rare and other species became more abundant.

Along with the change in microbiome composition, they also observed thinning of the gut mucosal layer from the WSD deprived of fiber. The gut mucosal layer is a protective layer between the gut cells and the gut bacteria, which prevents the cells from having direct contact with the bacteria. Thinner gut mucus layers are less protective and more easily penetrated by gut bacteria, which can cause an increase in gut inflammation.

thinning of mucus layer on a WSD over 28 days [7]

thinning of mucus layer on a WSD over 28 days [7]

Increased blood glucose and insulin levels in mice on WSD [7]

Increased blood glucose and insulin levels in mice on WSD [7]

Only a short time later, the mice on the WSD developed chronic immune reactions due to the thinner mucus layer and more permeable gut cell wall.
Together with the chronic inflammation, Dr. Gewirtz and his colleagues observed that the mice started to gain fat and developed high blood sugar levels.

To counter-attack the degrading health of the mice, both research groups added fermentable (soluble) fiber into the diet of mice but kept the animals on a high-fat diet to check if fiber alone can reverse the adverse affects of the WSD.
The scientists discovered that a diet high in fiber restored the protective mucus layer, protected against inflammation and lowered the mice's blood sugar levels.

Western Style diet, which is high in fat and low in fiber leads to microbiome alterations, reduced mucus thickness, and a permeable gut. Symptoms are reversible by adding fiber and probiotics. [7]

Western Style diet, which is high in fat and low in fiber leads to microbiome alterations, reduced mucus thickness, and a permeable gut. Symptoms are reversible by adding fiber and probiotics. [7]


Human Studies on Fiber

Fiber promotes weight loss

A diet with 4 grams extra fiber leads to more weight loss [9]

A diet with 4 grams extra fiber leads to more weight loss [9]

These mice studies show us how important adequate dietary fiber intake is, but let’s switch gears a little and look into studies on humans that show us the advantages of a diet high in fiber!

A study looked at the diet of approximately 1800 Americans and found that a diet high in fiber was strongly correlated with lower body-mass indexes [8].
In another double-blind study, overweight participants were given 4 grams of fiber extra per day or a placebo [9]. After 12 weeks the fiber-group lost on average about 700 grams more body weight than the placebo group!
The researchers also checked the participants' satiety levels and found that the participants in the fiber group were more satiated by their meals than the participants in the participants in the placebo group. The latter finding is also supported by a study published in the New England Journal of Medicine, which shows that high fiber intake reduces appetite [10].

Fiber can help prevent diabetes

Fiber dampens insulin secretion [11]

Fiber dampens insulin secretion [11]

 Patients with type 2 diabetes (T2D) have to be cautious to not spike their insulin levels - which is also important for lose weight, by the way.
Fiber-rich foods slow down the uptake of the carbohydrates, thereby reducing insulin spikes.

In a study published in 1978, volunteers consumed 50 g of liquid glucose with and without 12 grams of extra fiber. The fiber exhibited a clinically meaningful decrease in blood glucose and insulin concentrations compared to the consumption of liquid glucose alone [11]. This study indicates that one of the reasons why fructose in fruits is absorbed differently than fructose consumed from juices or sodas devoid of fiber.

The publication list of research studies on the connection between fiber and T2D is long and a meta-analysis of 17 studies showed that the risk of T2D was significantly decreased with higher total dietary fiber intake [12].

High dietary fiber intake prevents cardiovascular diseases

Fiber reduces the risk of Cardiovascular diseases [13]

Fiber reduces the risk of Cardiovascular diseases [13]

Another modern disease is strongly associated with fiber intake: Cardiovascular Diseases.
A meta-analysis looked into 22 research studies focusing on fiber and the development of cardiovascular diseases, and found that eating on average 20 grams of fiber per day instead of 10 grams can reduce the risk of cardiovascular diseases by around 50%.  Higher levels of fiber consumption further decreases the risk of cardiovascular diseases [13].


Can fiber protect from cancer?



Cancer remains one of the leading causes of death in the world and even though many cases of cancer are more "bad luck" than anything else, there are a few types of cancer that are strongly associated with environmental causes, such as smoking for lung cancer or nutrition for colorectal cancer [14].
In the early 70s, Dr. Burkitt made an interesting observation when he found that the incidences of colorectal cancer are strongly connected to where people live.
Dr. Burkitt showed that European and American people have up to 10 times more colorectal cancer compared to people living in Africa [15].

Fiber and Colorectal cancer_Aune_BMJ.PNG

To exclude genetic effects, Dr. Burkitt looked into African and Asian people who migrated to the United States. Not surprisingly, they had a comparable number of colorectal cancers as Americans.
40 years after Burkitt's observations, a huge meta-analysis of 25 studies confirmed Burkitt's findings, indicating that the incidence of colorectal cancer is reduced by 10% with every 10 grams of daily fiber intake [16].


Does Fiber promote longevity?

Indeed, the benefits of fiber seem to overwhelm most expectations: a journal review looked into seventeen different studies that had a total of almost 1 million cohort members and nearly 70,000 death and found that “there was a 10% reduction in risk of all-cause mortality per 10-g/day increase in fiber intake” [17].

How much fiber should you consume and from which sources?

The FDA recommendation for daily fiber intake is around 30 grams. However, I certainly consume more than this on most days. On some days actually between 50 and 60 grams. Our bodies are evolutionarily adjusted to tolerating higher amounts of fiber. Researchers found that our ancestors had a dietary fiber intake some days as high as 135 grams/day of a particular kind of fiber [18].

Great sources of fiber are many non-processed foods. Fruits and especially vegetables are great natural sources, but fiber supplements also suffice.

I love to workout and whenever I needed to go on a diet, I only focused on restricting calories and simultaneously, increasing my protein intake. In the past dieting was awful because I would never feel full. During my diets I was also prone to getting colds and my bowel movements slowed down. Changing to a diet with a focus on eating fiber in the form of vegetables made losing much easier and more enjoyable because it helps to keep me full and my gut bacteria happy and helpful. 

For more information on how the microbiome and a diet rich in fiber can help you to lose weight, check out my blog about it:

Is your gut microbiome making you fat?





  2. King et al., Trends in dietary fiber intake in the United States, 1999-2008.,J Acad Nutr Diet, 2012

  3. Menni et al., Gut microbiome diversity and high-fibre intake are related to lower long-term weight gain, International Journal of Obesity, 2017

  4. Macfarlane et al., Review article: prebiotics in the gastrointestinal tract, AP&T, 2006

  5. Säemann et al., Anti-inflammatory effects of sodium butyrate on human monocytes: potent inhibition of IL-12 and up-regulation of IL-10 production, FASEB Journal, 2000

  6. Zou et al., Fiber-Mediated Nourishment of Gut Microbiota Protects against Diet-Induced Obesity by Restoring IL-22-Mediated Colonic Health, Cell, 2018

  7. Schroeder et al., Bifidobacteria or Fiber Protects against Diet-Induced Microbiota-Mediated Colonic Mucus Deterioration, Cell 2018

  8. Shay et al., Food and nutrient intakes and their associations with lower BMI in middle-aged US adults: the International Study of Macro-/Micronutrients and Blood Pressure, The American Journal of Clinical Nutrtion, 2012

  9. Salas-Salvado et al., Effect of two doses of a mixture of soluble fibres on body weight and metabolic variables in overweight or obese patients: a randomised trial, British Journal of Nutrition, 2008

  10. Burton-Freeman, Dietary Fiber and Energy Regulation, The Journal of Nutrition, 2000

  11. Jenkins et al., Dietary fibres, fibre analogues, and glucose tolerance: importance of viscosity, British Medical Journal, 1978

  12. Yao B et al. Dietary fiber intake and risk of type 2 diabetes: A dose- response analysis of prospective studies. Eur J Epidemiol. 2014

  13. Threapleton et al., Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis, BMJ, 2013

  14. Tomasetti and Vogelstein, Variation in cancer risk among tissues can be explained by the number of stem cell divisions, Science, 2015


  16. Aune et al. Dietary fibre, whole grains, and risk of colorectal cancer: Systematic review and dose- response meta-analysis of prospective studies. BMJ. 2011

  17. Yang et al., Association Between Dietary Fiber and Lower Risk of All-Cause Mortality: A Meta-Analysis of Cohort Studies, Am J Epidemiol

  18. Leach and Sobolik, High dietary intake of prebiotic inulin-type fructans in the prehistoric Chihuahuan Desert, British Journal of Nutrition, 2010