If you have been with me so far this year, you probably knew this article was inevitable.  While much of the wellness world has been star-struck by low carb, ketogenic, or other fad diets, I haven’t heard much about fiber outside medical conferences and research papers.

Digestive and metabolic complaints are two of the most common concerns people seek advice for, and a lot of the advice given is unfortunately based upon opinion or one person’s personal experience - you see this in book and blog form very frequently.  I do not exclude myself from those who have made these errors of judgement; fortunately, we all have the option of growing and learning from our mistakes!

Let’s face it: fiber isn’t exactly sexy.  Increasing your fiber doesn’t put your body through a roller coaster that can result in a rapid 20 pound weight loss, nor does it create massive shifts in inflammation overnight like some medications and fasting can.  Increasing fiber means increasing healthy whole food carbohydrates, and we have been assured that carbs are our enemy by the current trends in wellness. 

With our chronic deficiency in fiber, adding it to our diet can be difficult.  Increasing fiber too quickly can make you feel quite uncomfortable with bloating, abdominal pain, and embarrassing gas.  Increasing fiber without increasing fluid intake can also be constipating and frustrating.  

It’s not surprising that “More than 90 percent of women and 97 percent of men do not meet recommended intakes for dietary fiber.” (1)  Let’s take this opportunity to better understand what fiber is, what it can do for us, review the best available evidence to see why increasing fiber is a must for long-term health, and develop a strategy for increasing our fiber intake without causing ourselves unnecessary discomfort or embarrassment. 

What is Fiber

Before we start talking about all of the wonderful things fiber can do for us, let’s talk about what fiber actually is.  “Dietary fiber is a diverse group of compounds, including lignin and complex carbohydrates, which cannot be digested by human enzymes in the small intestine.” (2)  Dietary fiber means the fiber you eat that is found in its natural form in food.  

Fiber is only found in plants.  Refined carbohydrates are grains that have had their fiber removed to make them lighter and fluffier such as white “all purpose” flours and white rice.  Lignin is found in abundance in the coverings of seeds like flax seeds.  The presence of lignin makes flax seeds indigestible unless they are ground to break up that outer seed coat and expose the inner digestible parts. 

In addition to dietary fibers, there are also functional fibers which are created by people.  We find these added to foods as bulking agents or sold as nutritional supplements. Examples of functional fibers include chitin which is an isolated component of insect and seafood shells, psyllium which is extracted and concentrated from plantain seeds, polydextrose which is created through randomized chemical polymerization of sugars. (3)

The effects that different fibers have are determined by three different qualities.  A fiber can dissolve in water or it can't: solubility.  Some fibers will absorb water and create a gel-like effect: viscosity.  Finally, some fibers can be digested by our gut microbes and some exit our bodies largely unchanged: fermentability. 

Soluble vs insoluble fiber

Soluble fibers can be dissolved in water.  This is often a selling point for functional fibers sold as dietary supplements.  Psyllium is a good example of this; it is also a viscous fiber meaning it will thicken your water if not consumed immediately.  Other soluble fibers include Beta-glucans from oats and barley, inulin from burdock root, and resistant starches found in produce such as bananas.  

Soluble fibers have health benefits that extend beyond the digestive tract.  We will explore this in more detail below. 

Viscosity 

All viscous fibers are soluble, but not all soluble fibers are viscous.  Inulin is an example of a fiber that is soluble but is not viscous.  Viscosity results from a fiber’s ability to bind to and absorb water similarly to gelatin.  Pectin, found abundantly in berries, is a good example of a viscous fiber that we can use to make jams and jellies. 

Fibers that are viscous have the benefit of increasing in size in our stomach helping us feel full sooner.  They also slow the rate at which our stomachs empty which helps us feel fuller longer. 

Fermentability 

If a fiber is fermentable, it can be digested by our gut microbes into short-chain fatty acids and other beneficial compounds that exert health effects on our gut, our immune system, and can even send signals through our enteric (gut) nervous system to our brain affecting our mood, the clarity of our thoughts, and overall inflammation. 

There are a few non-fermentable fibers, such as wheat dextrin and cellulose, that stay mostly intact as they travel through our digestive tracts.  These fibers help increase the bulk of our stool and have a positive effect on the regularity of bowel movements.  

Fiber for Disease Prevention

Take a stroll down the cereal aisle of your local grocery store and you may notice the heart healthy label on several different cereals.  This is an FDA-approved label that can be applied to foods that are low in cholesterol and fat and have significant amounts of soluble fiber. (2)  

Soluble fiber has been shown to lower cholesterol and blood pressure levels.  Not only this, studies, that have been reproduced, have shown that for each 7 grams of fiber eaten, the risk of heart disease is lowered by 9%! (2)  This is all fantastic as heart disease is the number one killer in the US, but there is so much more to fiber than just cardiovascular disease.  Ready for a too good to be true sounding list? 

A diet replete with fiber lowers the risk of heart disease; Type-2 diabetes; metabolic syndrome/insulin resistance; ovary, breast, esophagus, stomach, colon, and pancreatic cancers; diarrhea in patients fed through tubes; fecal incontinence; decreases hunger; helps with weight loss; and lowers all-0cause mortality (death). (2)

You can see why eating enough fiber is my go-to recommendation for overall health.  Now let’s see why it’s also my recommendation for the treatment of several diseases.

Fiber for Treatment of Disease

For this section, I’m just going to summarize the findings that I reviewed for this article to save us all some time - you know how wordy I can get!

Fiber has been used used to treat the following conditions: 

Diabetes:

•  total fiber consumption of 20+ grams per 1,000 Calories lowered after-meal blood sugar 13-21%, LDL 8-16%, and triglycerides 8-13% compared to a diet with 10 or fewer grams total fiber per 1,000 calories. (2) 

• “Delayed gastric emptying may also reduce postprandial blood glucose concentrations and potentially have a beneficial effect on insulin sensitivity.” (3)

• Increased fiber intake has been shown to reduce fasting blood sugar, Hemoglobin A1c levels, post-prandial blood glucose and insulin levels without causing hypoglycemia in healthy subjects. (2)

Irritable Bowel Syndrome: 

• strongest effect seen with reduction of FODMAPs and increase in psyllium. (2)

Constipation: 

• “Large/coarse insoluble fibers (e.g., wheat bran) and nonfermentable, soluble gel-forming fibers (e.g., psyllium) can have a potential laxative effect.” (2)

Hemorrhoids: 

• psyllium may slow disease progression and reduce the number of bleeding episodes. (2)

Metabolic Syndrome: 

• “Soluble gel-forming fibers, such as psyllium and fibers found in oat products, can lower serum LDL cholesterol concentrations and normalize blood glucose and insulin responses.” (2)

Systemic Inflammation: 

• Bacterial fermentation of fiber produces short chain fatty acids which act as chemical messengers and create an anti-inflammatory effect on the immune system that balances and regulates immunity. (4)

Ulcerative Colitis: 

• In addition to all of the above, we also see a relationship between fermentable fibers and Inflammatory Bowel Disease.  Remember how fermentable fibers are acted on by our gut microbes and broken down into short-chain fatty acids?  One that is produced in abundance is butyrate. “Butyrate [...] is the preferred energy source for colon cells, and lack of butyrate production, absorption, or metabolism is thought by some to contribute to ulcerative colitis.” (3)

Fiber and Weight Management

Fiber can aid in weight management in several different ways.  

• First, fiber is non-digestible meaning it has no caloric value, so you get more volume to your food without added calories.  This means a meal full of fiber-rich foods will provide fewer calories by volume, allowing you to eat until you are fully satisfied.  For example, you could eat 3.5 chocolate kisses, 12 standard gummy bears, or 100 raspberries and each would amount to 100 Calories. (5)  Each of these options would feel different in your stomach and be enjoyed over a different amount of time. 

• Second, fiber slows the rise and fall of blood sugar reducing sugar cravings and crashes.  This means fewer hangry episodes and better blood sugar control. 

• Third, with viscous fiber, it will actually expand in volume once mixed with water in your stomach which slows the rate at which food is emptied from your stomach, helping you feel full longer. 

• Fourth, remember those gut microbes?  When they are starving for fiber, they produce fewer short-chain fatty acids.  This means our brain doesn’t get signals from our gut that trigger satiety, the feeling of having enough.  This results in us eating more as our body and our microbes demand nutrients. 

Applications

Unfortunately, low fiber is the norm in U.S. diets and is especially low in those consuming a low carbohydrate diet. (2)  The epidemic of preventable disease killing our population is growing each year.  We see similar rates in these preventable diseases in populations that switch from more plant-based eating patterns to one that resembles our Standard American Diet.  The link between illness and diet is very clear and easy to see - even if food companies do their best to hide the truth. 

Fiber intake recommendations have historically been divided into general recommendations for men (38 grams) and women (25 grams) - this is too simplistic and binary!

A good goal for fiber intake is 20 grams or more for each 1,000 calories eaten.  This is the level where we see the most benefit on cholesterol and blood sugar levels.  Those 20 grams should include soluble and insoluble fibers, so simply adding psyllium to your water isn’t going to work.  It should also be noted that research has found no upper limit for fiber intake.  Some populations safely eat upwards of 100 grams of fiber daily and do not see nearly the same rates of cancer, diabetes, cardiovascular disease, or other preventable illnesses! (6) 

Legumes are particularly high in fiber with one cup of black beans holding 15 grams of fiber.  Chia seeds contain 10 grams of fiber per ounce, one cup of whole wheat spaghetti has 6 grams of fiber, and 1 medium potato has 4 grams of fiber.  That already puts us at 35 grams and we haven’t even included fruits or veggies yet!  Raspberries have 8 grams of fiber per cup and broccoli has 5 grams of fiber per cup.  You can see how a whole-foods-plant-based diet will get you to your fiber goal pretty effortlessly. (7)

However, making drastic and rapid changes to our diet doesn’t come without side effects.  Quickly increasing fibers like inulin and polydextrose can cause abdominal pain, gas, bloating, and flatulence. (2)  Furthermore, those with known issues of digestive dysmotility who eat large amounts of insoluble fiber have been known to develop dangerous and painful intestinal blockages.  If you have diabetes or a degenerative neurological condition and have frequent issues with digestion, it’s a good idea to ask your doctor if you may have a dysmotility issue as they are more common with these conditions.  The good news is that you can increase your fiber in a sustainable and manageable way to avoid these complications. 

To decrease side-effects, increase your fiber slowly and increase your water consumption.  Also, opt for whole foods instead of foods fortified with extra functional fibers or fiber supplements, as all plant foods contain a combination of soluble and insoluble fibers. 

“Some strategies for increasing dietary fiber intake include increasing fruit and non-starchy vegetable intake, increasing intake of legumes, eating whole-grain cereal or oatmeal for breakfast, substituting whole grains for refined grains, and substituting nuts or popcorn for less healthy snacks.” (2)

You also may have heard about the link between high fiber intake and the absorption of medications or minerals.  This can be an issue especially with functional fibers.  A good plan is to take your medications and eat your high fiber meals at different times if advised by your doctor/pharmacist.  As for minerals, mineral absorption is theoretically reduced by increased fiber consumption, however at rates of 10-12 grams of fiber/1,000 Calories, no reduction in mineral levels has been seen in studies.  If you have a condition such as osteoporosis or iron deficiency and you are taking mineral supplementation therapeutically, opt to take those supplements away from high fiber meals and consider taking them with high vitamin C foods as this can assist in absorption. 

Next Week

Next week, let’s talk about the other side of the carbohydrate spectrum - sugar. 

References

1. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov. 

2. Higdon, J, “Fiber” Linus Pauling Institute, 2004, Updated March 2019 by Delage, B https://lpi.oregonstate.edu/mic/other-nutrients/fiber Accessed 3/15/2021

3. Institute of Medicine 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington,DC: The National Academies Press. https://doi.org/10.17226/10490

4. Rooks, M., Garrett, W. Gut microbiota, metabolites and host immunity. Nat Rev Immunol 16, 341–352 (2016). https://doi.org/10.1038/nri.2016.42

5. https://www.foodnetwork.com/healthy/photos/foods-with-100-calories

6. Kieran M. Tuohy, Christos Gougoulias, Qing Shen, Gemma Walton, Francesca Fava and Priya Ramnani, “ Studying the Human Gut Microbiota in the Trans-Omics Era - Focus on Metagenomics and Metabonomics”, Current Pharmaceutical Design (2009) 15: 1415. https://doi.org/10.2174/138161209788168182

7. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/high-fiber-foods/art-20050948