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What Thyroid Sufferers Need To Know About Fiber, Resistant Starch, and SCFA

Published November 13 2017

Many people with thyroid and autoimmune thyroid conditions don’t eat enough fiber.  And while it might seem easy enough to add more fiber to your diet, for some people this is easier said than done.  Is it best to get fiber through foods, or through a fiber supplement?  What are the best food sources of fiber?  And how can those who follow an autoimmune Paleo diet get sufficient fiber when they are unable to eat certain fiber-rich foods such as legumes and nuts?  I intend to answer these questions, and cover other things related to fiber intake, so that hopefully by the time you’re done reading this article you will have a better understanding of why fiber is important, along with the difference between fiber, resistant starch, and short chain fatty acids (SCFA).

One of the main characteristics of fiber is that digestive enzymes are unable to break down the fiber into monosaccharides, and as a result the fiber passes through the digestive tract mostly intact.  Although I’m going to discuss some of the specific benefits of fiber later in this article, two of the main functions of fiber are to feed the good bacteria in the gut and to add bulk to the stool.  With regards to feeding the good bacteria, you probably have heard about prebiotics, and all prebiotics are considered to be a type of fiber.  Resistant starch is considered to be a type of prebiotic.  And since all prebiotics are fiber, and resistant starch falls under the category of prebiotics, then this means that resistant starch is a type of fiber.

In an attempt to make it easier to understand, let’s look at the different types of fiber and discuss the characteristics:

Soluble fiber.  Soluble fiber attracts water and turns to a gel during digestion (1) [1].  In other words, it gets dissolved during the digestive process, which is why it’s referred to as being soluble.  This type of fiber is found in foods such as oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables (1) [1].  Psyllium is also a form of soluble fiber (1) [1].

Pectin, gums, and fructans are soluble types of fiber.  With regards to fructans, short chain fructans are referred to as fructooligosaccharides, whereas longer chain fructans are called inulins.  Food sources of fructan include chicory, Jerusalem artichokes, and onions.  Beta-glucans, which are prominent in mushrooms, but are also found in certain grains and some types of seaweed, are mostly soluble.  In general soluble fiber provides better support for blood sugar balance and cardiovascular health when compared to insoluble fiber.

In general, soluble fibers are more completely fermented and have a higher viscosity than insoluble fibers. However, not all soluble fibers are viscous (e.g., partially hydrolyzed guar gum and acacia gum) and some insoluble fibers may be well fermented (1) [1].  But what is the difference between viscous soluble and non-viscous soluble fiber?  Well, soluble fibers that are viscous are “gel-forming”, and they have greater cardiovascular benefit than non-viscous soluble fibers.  In fact, viscous soluble fiber can bind with cholesterol and help with its excretion in the stool.

Insoluble fiber.  While soluble fiber seems to play a greater role in cardiovascular health, as well as helping to regulate blood sugar levels, insoluble fiber adds bulk to the stool, and thus seems to provide a greater benefit in the prevention of constipation.  Food sources of insoluble fiber include wheat bran, vegetables, and whole grains.

However, it’s important to understand that while some foods can be classified as being strictly “soluble” or “insoluble”, many foods will have a combination of different types of fiber.  For example, although beans and other types of legumes are excluded from both a standard paleo and autoimmune paleo diet, it’s worth mentioning that they are good sources of fiber.  And most beans will include both soluble and insoluble fiber.  This also describes most vegetables, as most have both soluble and insoluble fiber, although the starchy vegetables are typically higher in soluble fiber.

Resistant starch.  This is insoluble and isn’t broken down by digestive enzymes, and thus reaches the large intestine and is fermented by bacteria, which classifies it as a type of fermentable fiber.  There are four categories of resistant starch, known as RS1, RS2, RS3, and RS4 (2) [2].  RS1 is found in whole grains and legumes.  RS2 consists of foods such as raw potatoes and high-amylose corn starch.  Examples of RS3 foods include potatoes cooled after cooking.  RS4 are found in breads and cakes.  Food sources of resistant starch include plantains, potatoes, and legumes.

Short chain fatty acids (SCFA).  The main SCFA include acetate, proprionate, and butyrate.  When you eat resistant starch the good bacteria will feed on this and will produce SCFA through fermentation.  Bacteria in the colon use these short chain fatty acids as their energy source, with butyrate being the main SCFA.  The production of SCFA can also help to reduce inflammation, and they can inhibit the growth of pathogenic organisms by reducing luminal and fecal pH (3) [3].  SCFAs also help regulate sodium and water absorption, and can increase the absorption of certain minerals such as calcium, magnesium, copper, zinc, and iron (3) [3].

How SCFAs Can Benefit Graves’ Disease and Hashimoto’s Thyroiditis

SCFAs also have anti-inflammatory effects, and they play a role in the regulation of immune system function.  For example, there is evidence that butyrate can help to increase regulatory T cells, while decreasing Th17 cells (4) [4].  I’ve discussed these immune cells in other articles and blog posts, as a high number of Th17 cells are commonly seen in autoimmune conditions, while regulatory T cells help to suppress autoimmunity.  As a result, increasing SCFA such as butyrate can have a suppressive effect on the autoimmune component of Graves’ Disease and Hashimoto’s Thyroiditis.

What Are The Health Benefits Of Fiber?

What I’d like to do now is talk about some of the health benefits of fiber.

Cardiovascular health.  There is evidence that fiber can help to reduce the risk of developing cardiovascular disease.  One meta-analysis consisting of eighteen studies showed that the consumption of dietary fiber is inversely associated with the risk of developing coronary heart disease (5) [5].  Another meta-analysis also showed that high dietary fiber intake is associated with a reduced risk of mortality from CVD, along with all cancers (6) [6].  A study involving Swedish adults showed that intake of dietary fiber, especially fruit and vegetable fibers, is inversely associated with risk of stroke (7) [7].  Elevated levels of C-reactive protein (CRP) increase one’s risk of developing cardiovascular disease, and there is evidence that increased consumption of dietary fiber can reduce CRP (8) [8] (9) [9].

Prevention of Type 2 Diabetes.  Some suggest that diets that are high in insoluble fiber may offer the best protection against type 2 diabetes, and fruits and vegetables are high in cellulose, which is a type of insoluble fiber (10) [10].  On the other hand, soluble fiber delays glucose absorption from the small intestine and thus may help prevent the spike in blood glucose levels that follow a meal or snack (10) [10].  A meta-analysis showed that a higher intake of high fiber fruits and vegetables (berries, green leafy vegetables, yellow vegetables, cruciferous vegetables) is associated with a lower risk of type 2 diabetes (11) [11].  Another study showed that fiber can help in those who already have diabetes by reducing fasting blood glucose and hemoglobin A1C (12) [12].  Another meta-analysis involving eight European countries showed dietary fiber intake was associated with a lower risk of diabetes (13) [13].

Improves overall gut health.  Dietary fiber is partially or completely fermented by the gut microbiota.  In other words, it feeds the good bacteria of the colon.  In addition, eating different types of fiber-rich foods will increase the diversity of the microbiota, which also is beneficial in preventing dysbiosis and an increase in intestinal permeability.

Maintaining a Healthy Body Weight.  As mentioned earlier, eating a high fiber diet can increase the diversity of the microbiome.  This in turn can increase energy metabolism and play a role in losing weight (14) [14].  Another study discussed how the average fiber intake of adults in the United States is less than half of the recommended levels, and increasing the consumption of dietary fiber is a critical step in preventing obesity (15) [15].  Of course this isn’t to suggest that eating fiber alone will be the only solution for those who are overweight and obese, but it is yet another piece of the puzzle to consider.

Cancer.  There is some evidence that dietary fiber can prevent certain types of cancers from developing.  This includes breast cancer (16) [16], prostate cancer (17) [17], colorectal cancer (18) [18], and possibly even pancreatic cancer (19) [19].  This doesn’t mean that increasing one’s fiber intake alone will prevent someone from developing these and other types of cancers, but sufficient dietary intake is one important factor in the prevention of cancer.

How Much Fiber Should You Consume Each Day?        

The recommended fiber intake for children and adults is 14 grams of fiber per 1,000 calories (20) [20].  So according to this, if you consume an average of 2,000 calories per day then you should be eating 28 grams of fiber per day.  If you average 2,500 calories per day then you should aim for 35 grams of fiber per day.  If you aren’t sure how many calories you consume on a daily basis you can use a free program such as www.myfitnesspal.com, where you can enter your food diary and it will tell you approximately how many calories you consume on a daily basis.  In fact, you can also use MyFitnessPal to keep track of how much fiber you are consuming, although you will have to change the default settings.

However, some sources suggest that we need to consume more fiber than this.  There is some evidence that our ancestors ate up to 100 grams of fiber each day (21) [21]!  I don’t expect anyone to eat this much fiber, but there is justification to aim for at least 50 grams of fiber consumption per day.

Fiber and The Autoimmune Paleo Diet

Some of the best food sources of fiber are excluded from an autoimmune Paleo diet.  This includes nuts, seeds, legumes, and grains.  This of course can make it challenging to get sufficient fiber from your diet if you have Graves’ Disease or Hashimoto’s Thyroiditis and are following a strict autoimmune paleo diet.  So where should people with autoimmune conditions get their fiber from if they are following a strict AIP diet?  Vegetables and fruits are the main sources, which is why you want to make sure you eat a sufficient amount of these foods.  Some of the vegetables and fruits with the greatest amount of fiber include broccoli, artichokes, Brussels sprouts, turnips, avocados, berries, and apples.

The problem is that most people don’t eat enough servings of vegetables per day.  And the type of vegetables you eat, as well as fruit can make a difference.  For example, one ½ cup serving of broccoli will provide more fiber than one cup of romaine lettuce or spinach.  With regards to fruit, a medium apple or pear will have a lot more fiber than one cup of grapes.  Keep in mind that you can also get fiber through starches such as plantains and sweet potatoes.

In order to make sure you are eating enough foods high in fiber I’ll go ahead and list some of the top high-fiber foods that can be eaten by those who are following an autoimmune Paleo diet:

AIP-Friendly Foods Highest In Fiber:

Should You Take a Fiber Supplement?

If you have regular bowel movements then this is a good sign that you are getting enough dietary fiber, and as a result you probably don’t need to take a fiber supplement.  But how about if you are dealing with constipation?  Well, there can be numerous factors which can cause constipation, and low dietary fiber is definitely one factor.  As a result, if you are not having regular bowel movements, or if you are having regular bowel movements but are straining, then it might be a good idea to take a fiber supplement.  However, you of course don’t want to rely on taking fiber supplements, and so please make sure you are also eating plenty of fiber-rich foods.  Sometimes magnesium citrate can also help with constipation, and you of course want to make sure you drink plenty of water.   If constipation is an issue I would read an article I wrote a few years ago entitled “Chronic Constipation and Natural Treatment Methods [22]”.

What Approach Should You Take If You Have SIBO?

Many of the high fiber foods are problematic for those people who have small intestinal bacterial overgrowth (SIBO).  This is especially true with soluble fiber (including resistant starch), as insoluble fiber isn’t fermented by bacteria.  As a result, those people with SIBO will need to minimize their consumption of soluble forms of fiber, and might need to completely avoid it.  But with that being said, if you have SIBO you need to listen to your body, as while there are people with SIBO who can’t eat any soluble fiber, some people are able to eat small amounts of these foods.  For example, someone might do fine eating ½ cup of steamed broccoli, but if they exceed this amount they may experience a lot of digestive symptoms.  And the same concept applies to other foods high in soluble fiber.

In summary, most people don’t eat enough fiber, and this includes those with thyroid and autoimmune thyroid conditions.  In fact, many people with Graves’ Disease and Hashimoto’s Thyroiditis follow an autoimmune paleo diet, which excludes some of the best sources of fiber, including nuts, seeds, and legumes.  As a result, people who follow this diet need to eat plenty of fruits and vegetables to get enough fiber, along with some types of starch.  Some of the different types of fiber include soluble fiber, insoluble fiber, and resistant starch.  Fiber has numerous health benefits, and while sometimes taking a fiber supplement can be beneficial, you want to try to get most of your fiber from the food you eat, which will allow you to get a variety of soluble and insoluble fiber, along with resistant starch.