Fat-soluble toxins are more likely to be eliminated this way since they will be bound up in bile. Fiber also aids in the elimination of heavy metals through directly binding to them and then moving them through the system and out of the body.
Detox. It is a popular word in health circles, but it remains a controversial one in some areas. As I’ve discussed before, there is a debate as to whether we really need to undergo special detox diets or programs when our bodies already have a system in place to get rid of toxins and waste.
Although there may be pathways in place, we do need to support them, especially in an increasingly toxic world. One of the key processes in detoxification, also known as biotransformation, is the final step: elimination. It is in this step that fiber becomes a vital player.
There are many reasons for including fiber in your diet to improve your health. However, more research is pointing to the differences among the different fibers, which may just mean that it is important to think about what type of fiber you consume…as well as ensuring you consume a variety so you really do benefit from all the possible health benefits of fiber, including aiding in the elimination of toxins.
Fiber 101
Before we jump into fiber’s role in detoxification, let’s take a quick moment for a basic rundown on all things fiber so we all start off on the same page.
A simple definition of fiber is a carbohydrate that humans cannot digest. Although it may not be broken down and absorbed for nutrients, it does play a key role—actually several—in health and wellness. Plant foods (including fruits, vegetables, beans, legumes, whole grains, seeds, and nuts) contain fiber, although there is not just one singular type of fiber. Fiber can be broken down into two main categories:
Soluble fiber – The type which water mixes with to create a gel-like substance in your intestines. It aids in many areas of health, including helping to keep you full longer and reduce blood sugar spikes.
Insoluble fiber – Generally the type that passes through as is, being used to bulk up your stool to aid in its passage and elimination. You may have heard this colloquially called roughage.
Additional fiber classifications include fermentable or non-fermentable as well as viscous or non-viscous. The fermentable and non-fermentable categories address whether the commensal bacteria in your gut use the fiber as a fuel source or not. Both soluble and insoluble fibers can be used as fuel sources, although it is more common in soluble fibers. Viscous and non-viscous refers to the thickness of the gel-like substance formed from water and soluble fiber. The more viscous, the longer it sits in the gut, which further aids in slowing down digestion so you maintain feeling full longer.
Another important note is the difference between dietary fiber, which is that found naturally in foods, and functional fiber, which is the type added back into processed foods. There is also a variety of supplemental fibers, which are the powders and other forms of isolated fibers, and prebiotics, which are supplemental forms of the fermentable fibers.
Although fibers fall into the above categories, there are many different types. Examples of some of the more common types of fiber include:
Beta-glucans – found in cereal grains and mushrooms
Bran – outermost layer of cereal grains
Cellulose – found in plant cell walls
Chitins – cell walls of fungi as well as the exoskeletons of crustaceans and insects
Fructan – found in cereal grains
Galacto-oligosaccharides (GOS) – derived from lactose
Glucomannan – a water-soluble polysaccharide found in the cell walls of some plants
Inulin – a type of fructan; found in onions, chicory root, and Jerusalem artichokes
Lignin – found in plant cell walls and algae
Mannans – found in dates, aloe vera, green coffee bean seeds, and legumes
Oligofructose – a type of fructan derived from inulin
Pectin – found in beetroot, citrus peels, apples, peaches, pears, and cherries
Psyllium – a seed often used in supplemental fibers
You may have also heard of the term resistant starch when discussing fiber. What is its relationship with fiber? While resistant starch is not technically fiber, it can act like fiber because it does not get digested. It functions similar to soluble, fermentable fiber, helping to lower blood sugar and increase satiety as well as fuel your friendly bacteria.
As I’ve mentioned, fiber plays many roles in health and wellness. A few of the vital functions of fiber include:
Does the Type of Fiber Matter?
Although many studies on fiber simply look at the association between total dietary fiber consumption and certain health markers, not all fiber has the exact same function. Therefore, it is important to consume a variety of fibers rather than just one. Studies have begun to break down the type of fiber to determine which is best in certain situations for greater insight.
For example, in one community-based prospective study that looked at dietary fiber and cardiovascular disease risk factors, researchers found a different impact based on the dietary fiber consumed. The dietary fiber was divided into categories including grain, legume, vegetables, nuts, and fruits. Dietary fiber from vegetables, nuts, and fruits had an inverse relation to baseline CVD risk score. Those who had a higher intake of vegetable dietary fiber had lower triglyceride levels and TG/HDL-C ratio. Those with dietary fiber from fruits had an inverse relationship to changes in insulin and diastolic blood pressure, as well as higher HDL-C levels. Fiber from nuts had a negative association with weight changes, while none of the other ones did. Additionally, legume, fruit, and vegetable fiber, as well as a combination of the three, had an inverse relationship to CVD risk while grain and nut fiber did not. It should be noted that the grain fiber category did include processed grains and not just whole grains, which could have impacted the results. Furthermore, these food groups also have different nutrients and phytochemicals, which may have also affected the impact on health. However, this study does start to point to potential differences among the fiber found in different foods.
Another systematic review looking at the relationship of different fibers to blood pressure found that all fiber types had an association with lower systolic and diastolic blood pressure, but the greatest effect was with beta-glucans, which reduced systolic blood pressure by 2.9 mmHg and diastolic blood pressure by 1.55 mmHg compared to 0.9 mmHg SBP and 0.7 mmHg DSP for the pooled data for all fiber types. Interactions of the different fibers may also impact their fermentation in the gut and subsequent impact on health, which only further backs up the idea to consume diverse types of fiber if tolerated.
The main categories of soluble fiber and insoluble fiber may make it simpler to determine the best type of fiber to consume for a certain reason. In one study, soluble fiber had an inverse relationship with triglyceride and apolipoprotein B100 (ApoB100 a category of cholesterol) levels while insoluble fiber had an inverse association with blood pressure, total cholesterol, triglycerides, ApoB100, and the triglyceride to HDL ratio. In a systematic review looking at fiber as a treatment for IBS, soluble fiber led to a significant improvement in symptoms while in some cases, insoluble fiber led to an exacerbation of symptoms. Another study found that for chronic constipation, a mixture of soluble and insoluble fiber worked better than psyllium because it helped with relieving gas and bloating better, although both were equally efficacious. Another study found that supplementing with both soluble and insoluble fiber had a positive impact on bacterial diversity in the microbiome of mice.
Focus on Fiber and Detoxification: Does the Type Matter?
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As I briefly mentioned, a key role of fiber is to aid in the elimination of toxins. It does this in a few different ways. One way is simply by binding to bile to then removing them from the body. Fat-soluble toxins are more likely to be eliminated this way since they will be bound up in bile. Fiber also aids in the elimination of heavy metals through directly binding to them and then moving them through the system and out of the body. Other toxins may also bind directly to fiber rather than bile for elimination.
In today’s world, there is an array of environmental toxins we are exposed to that can cause oxidative stress and other harmful effects, leading to chronic disease in some individuals. Although some people do not present with any negative side effects of this exposure, other people quickly find they reach their toxic burden limit. In addition to the direct health impact of environmental toxins, they also can harm the gut microbiome, another reason why fiber may play a role in mitigating their effects.
No matter where you fall on this spectrum, it is important to maintain a proper functioning elimination route for your waste, including environmental toxins, endotoxins (the toxic byproducts of certain pathogenic bacteria in the gut), and endogenous waste such as hormones and metabolic waste. A few common toxins in today’s world include:
Benzene
Brominated flame retardants (BFRs and PBDE)
Dioxins
Formaldehyde
Heavy metals (cadmium, lead, mercury, arsenic)
Persistent organic pollutants (POPs) – Polychlorinated Biphenyls (PCBs) and organophosphate pesticides such as DDT
Pesticides and herbicides (glyphosate)
Plastics (BPA, phthalates, etc.)
Polycyclic aromatic hydrocarbons (PAH) – air pollution
Solvents
Environmental disease can impact many different organs and body systems, but there are ways diet and lifestyle can help mitigate some of the problems.
Although many studies do not specify the type of fiber required for improving biotransformation and elimination, or merely look at one and do not compare it to others, some studies do point to the unique detoxification capacities of different fibers:
Dietary fiber and PCBs : One study found that consuming foods rich in dietary fiber reduced exposure to PCBs in maternal and cord blood.
: One study found that consuming foods rich in dietary fiber reduced exposure to PCBs in maternal and cord blood. Dietary fibers and PCB: Another study comparing fiber types on toxin elimination (specifically PCB) in mice found that only the indigestible dextrin increased the level of PCB in the blood and that the fecal excretion was highest in the chitosan diet while fecal elimination was lower in the fermentable fiber group. None of the fibers led to a difference in the accumulation of the PCB. The fibers compared were cellulose as a control, fiber-free, rice bran, chitosan, and four fermentable fibers (lactosucrose, polydextrose, indigestible dextrin, and soybean polysaccharide). The researchers postulated that a combination of both soluble and insoluble fiber may have a greater impact on promoting excretion.
Another study comparing fiber types on toxin elimination (specifically PCB) in mice found that only the indigestible dextrin increased the level of PCB in the blood and that the fecal excretion was highest in the chitosan diet while fecal elimination was lower in the fermentable fiber group. None of the fibers led to a difference in the accumulation of the PCB. The fibers compared were cellulose as a control, fiber-free, rice bran, chitosan, and four fermentable fibers (lactosucrose, polydextrose, indigestible dextrin, and soybean polysaccharide). The researchers postulated that a combination of both soluble and insoluble fiber may have a greater impact on promoting excretion. FEBRA and toxins: One study on humans in Japan found that consuming FEBRA (fermented brown rice with Aspergillus oryzae) led to a decrease of 7, 33, 45, 36, and 26% of certain contaminants (DLPCBs, PCDDs, PCDFs, PCDD/DF TEQ, and total TEQ respectively). Comparatively, those not taking FEBRA eliminated 8, 28, 36, 31, and 20% of the same toxins respectively.
One study on humans in Japan found that consuming FEBRA (fermented brown rice with Aspergillus oryzae) led to a decrease of 7, 33, 45, 36, and 26% of certain contaminants (DLPCBs, PCDDs, PCDFs, PCDD/DF TEQ, and total TEQ respectively). Comparatively, those not taking FEBRA eliminated 8, 28, 36, 31, and 20% of the same toxins respectively. Inulin and cadmium : In one rat study, a symbiotic diet including the probiotics Bacillus coagulans and Lactobacillus plantarum with inulin reduced the metal accumulation in the liver and improved biochemical liver and kidney markers (demonstrating a protective effect against the toxicity of cadmium) as well as an increase in antioxidant activity.
In one rat study, a symbiotic diet including the probiotics Bacillus coagulans and Lactobacillus plantarum with inulin reduced the metal accumulation in the liver and improved biochemical liver and kidney markers (demonstrating a protective effect against the toxicity of cadmium) as well as an increase in antioxidant activity. Inulin and PCBs: Consuming inulin helps mitigate the negative impact on the gut microbiome by PCBs, thus providing a protective effect.
Consuming inulin helps mitigate the negative impact on the gut microbiome by PCBs, thus providing a protective effect. Lignin and T-2 toxin : Another rat study found that alfalfa, which is high in lignin, led to an increase in excretion of T-2 toxin, likely through binding the toxin to the intestinal lumen and promoting its excretion in feces.
: Another rat study found that alfalfa, which is high in lignin, led to an increase in excretion of T-2 toxin, likely through binding the toxin to the intestinal lumen and promoting its excretion in feces. Modified citrus pectin (MCP) and heavy metals: In one study in healthy individuals with normal levels of heavy metals in the body, consuming 15 g of modified citrus pectin led to a significant increase of the urinary excretion of arsenic in the first 25 hours, and after six days, there was a significant increase in cadmium urinary excretion. There was also an increase in lead excretion.
In one study in healthy individuals with normal levels of heavy metals in the body, consuming 15 g of modified citrus pectin led to a significant increase of the urinary excretion of arsenic in the first 25 hours, and after six days, there was a significant increase in cadmium urinary excretion. There was also an increase in lead excretion. Oat fiber and endotoxin: In one rat study, a combination of taurine and oat fiber significantly reduced the level of endotoxin in the portal vein compared to the control group. While there was a reduction in endotoxin levels in the treatment of taurine and oat fiber alone, there was an additive effect.
In one rat study, a combination of taurine and oat fiber significantly reduced the level of endotoxin in the portal vein compared to the control group. While there was a reduction in endotoxin levels in the treatment of taurine and oat fiber alone, there was an additive effect. Soluble fiber and bile acids: In one study on rats, soluble fiber increased the biliary excretion of bile acids while insoluble fiber decreased the elimination of bile acids. In another study, guar gum, lignin, and cholestyramine bound to bile acids while oat bran, wheat bran, and cellulose did not. Bile may contain some lipophilic toxins, so aiding in the elimination of bile can also aid in the excretion of toxins.
In one study on rats, soluble fiber increased the biliary excretion of bile acids while insoluble fiber decreased the elimination of bile acids. In another study, guar gum, lignin, and cholestyramine bound to bile acids while oat bran, wheat bran, and cellulose did not. Bile may contain some lipophilic toxins, so aiding in the elimination of bile can also aid in the excretion of toxins. Soluble fiber and heavy metals: In one in vitro study comparing soluble fiber and insoluble fiber, both from wheat bran, found that the insoluble fiber had higher capacity for binding heavy metal ions, although pH levels and fermentation both impacted the capacity for binding metals, as did amino acids and other minerals such as calcium, iron, zinc, and copper.
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In one in vitro study comparing soluble fiber and insoluble fiber, both from wheat bran, found that the insoluble fiber had higher capacity for binding heavy metal ions, although pH levels and fermentation both impacted the capacity for binding metals, as did amino acids and other minerals such as calcium, iron, zinc, and copper. Wheat bran and cadmium: In a mouse study, a diet of 10% wheat bran led to a reduction in cadmium toxicity. The bran bound most cadmium ions and prevented cadmium from entering the organs. There was also a reduction in the negative effects of cadmium on the gut microbiome.
In a mouse study, a diet of 10% wheat bran led to a reduction in cadmium toxicity. The bran bound most cadmium ions and prevented cadmium from entering the organs. There was also a reduction in the negative effects of cadmium on the gut microbiome. Wheat bran and PCB: In another rat study, wheat bran led to an increase in fecal excretion of PCB and lower retention of PCB in the body when PCB was also consumed. When PCB was no longer consumed, there was only a minor effect on fecal PCB and accumulation in the body was no longer impacted.
In another rat study, wheat bran led to an increase in fecal excretion of PCB and lower retention of PCB in the body when PCB was also consumed. When PCB was no longer consumed, there was only a minor effect on fecal PCB and accumulation in the body was no longer impacted. Wheat bran, flaxseed, and cadmium: In a mouse study comparing types of dietary fiber and cadmium absorption found that after a 30-day diet with either cellulose as a control, wheat bran, or flaxseed, the flaxseed group had a higher liver and kidney concentration of cadmium; however, it did not impact the toxicity of cadmium. In the wheat bran and flaxseed groups, cadmium also led to a decrease in the absorption of calcium and phosphorus while magnesium was increased in the flaxseed and wheat bran groups.
In a mouse study comparing types of dietary fiber and cadmium absorption found that after a 30-day diet with either cellulose as a control, wheat bran, or flaxseed, the flaxseed group had a higher liver and kidney concentration of cadmium; however, it did not impact the toxicity of cadmium. In the wheat bran and flaxseed groups, cadmium also led to a decrease in the absorption of calcium and phosphorus while magnesium was increased in the flaxseed and wheat bran groups. Wheat bran, pectin, and mercury: In one mouse study comparing wheat bran at 5, 15, or 30% of the diet, a 5% pectin diet, or a 5% cellulose diet, the wheat bran led to an increased rate of mercury elimination. The 15 and 30% bran diets led to a decrease of the total mercury concentration in the blood, brain, and small intestine, results which were only significant in the 30% bran diet.
This area of research remains in its infancy, with many studies still in the animal stage. However, one conclusion that can be made is that fiber does aid in the elimination of toxins…and that the type of fiber may be important.
Ultimately, consuming fiber from a variety of fiber sources, including both soluble and insoluble and fermentable and non-fermentable, will ensure you have a variety of fiber to aid in eliminating different toxins and protecting your gut microbiome from any negative impact from toxins. They may even work synergistically to enhance your detoxification capabilities.
So, in what ratio should you consume the different fibers? As with most things, the exact ratio and combination will change from person to person. In one small study, a 3:1 ratio of soluble to insoluble fiber led to more satiating effect in postmenopausal women, as well as lower insulin and CCK levels. Premenopausal women did not have a similar effect. Therefore, you will have to consider what benefits you want from fiber alongside your risk for toxic exposure, as well as any conditions you may have, to determine the right mixture. You may also simply make sure you consume a variety of whole, non-processed plant foods that contain fiber so you not only get sufficient fiber, you also benefit from the other beneficial nutrients and phytochemicals in the food.
That being said, in some situations, you may want to pay more attention to what type of fiber you consume. For example, if you know you are exposed to cadmium, then you may not want to consume as much flaxseed since studies have demonstrated that it may hold onto the cadmium for longer. If you need flaxseed for another reason, then make sure to balance it with other forms of fiber that will remove the cadmium from your body.
Those with IBS and other digestive disorders may need to have extra caution when adding fiber to their diet. Certain types may exacerbate symptoms, such as FODMAPs (low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols). However, studies have demonstrated that fiber, especially soluble fiber, can help with these disorders as well, so do not completely avoid fiber. Just find the type and amount that works for you.
General Recommendations for Fiber
25 – 35 g per day for adults
Build up slowly, especially if taking a supplemental form or prebiotic fibers, etc.
Don’t forget to drink plenty of water and other fluids to help with moving things through your intestines
Fiber, even from supplemental forms, is relatively safe. The biggest side effect is bowel tolerance, usually an increase in flatulence. Working slowly to build up bowel tolerance helps to reduce any negative side effects.
As always, if you plan to increase your fiber intake whether through foods or supplemental forms, talk with your doctor, nutritionist, or another healthcare practitioner beforehand to ensure you take the proper steps for your situation.
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Photo: Antoni Shkraba
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