This is Part 2 in a three-part series on the fascinating topic of FIBRE! Part 1 answered the question “what is fibre?” and explored the different categories of fibre and their health impacts. This Part 2 will explore the health benefits of the different types of fibre. In Part 3 I will share my top tips for increasing dietary fibre intake!

Health benefits of fibre

So what are the main health benefits of fibre? Before we kick off, I HIGHLY recommend you check out Part 1 of this series. It described the five (yes FIVE!!!) different categories of fibre. The health benefits of fibre depend on how they behave in the human body, and each of the five different types of fibre have their own unique pattern of behaviour in the human body, and therefore have their own unique health benefits. So go check out Part 1 and we’ll be here when you’re done!

Fibre can help you poop better - if you know which fibre to consume!

It may surprise you to know that not all types of fibre will help you poop. In fact, some types of fibre supplements have no laxative benefit at all, and some have actually been found to have a constipating effect.

Three types of fibre help you poop better. All of them are non-fermentable, and their beneficial action occurs in the large intestine/bowel:

1. Coarse insoluble fibre such as wheat bran whole, unprocessed or minimally processed grains like brown rice, bulgur wheat, and (genuinely) wholegrain flour, bread and pasta, beans and legumes (lentils, chickpeas), root vegetables, nuts and seeds;

2. Soluble, thickening/gel-forming, non-fermentable fibre such as psyllium; and

3. Soluble, non-gelling, non-fermentable fibre such as methylcellulose or calcium polycarbophil.

Insoluble fibre for constipation

Insoluble fibre particles like wheat bran travel through your digestive system, acting like tiny scrubbing brushes. They cause minor “irritation” to the lining of your large intestine which stimulates secretion of mucous and water (softening your stool) and speeding its transit. The larger/coarser the insoluble fibre particles, the greater the effect. In fact, it has been shown that if wheat bran is ground to a fine powder it can actually have a constipating effect. So go for whole unprocessed grains and veggies, or add a spoonful or two of wheat bran to your muesli, stews or baking.

Because insoluble fibre has no water holding/gelling properties, and because of its irritating/stimulating effect, it won’t help with diarrhoea and may actually make IBS or diarrhoea worse. If that is your problem, consider psyllium:

Psyllium for “stool normalising”

Soluble, viscous, non-fermentable fibre such as psyllium attract water to form a viscous gel in the digestive tract, which bulks and softens the stool, and retains its water content all the way through your bowel, producing a softer, easier-to-pass stool.

Unlike insoluble fibre, psyllium, due to its gelling, water-holding properties, has a bidirectional “stool normalising” effect. If your stool is too hard it will soften it, of it is too loose it will firm it.

Fermentable fibres won’t help you poop

Fermentable fibres are amazing! They serve as food for the healthy tiny microbes that live in our large intestine. We need lots of healthy “good guy” bacteria to keep the less-healthy bacterial strains like e.coli in check. We also need the amazing short chain fatty acids (SCFA’s) our healthy bacteria excrete. But… fermentable fibres like just don’t deliver the laxative or stool normalising benefits of insoluble fibre or psyllium, respectively.

And there’s another potential problem with fermentable fibre which I need to cover - in addition to excreting SCFA’s with their myriad health benefits, the healthy little microbes in our large intestine can also excrete GAS. Some of us cope with the gas produced by our gut microbes better than others. For people with IBS, consuming certain types of fermentable fibres, or consuming them in large amounts, can result in terrible pain. So if you have an irritable bowel that doesn’t cope with gas, don’t completely cut out fermentable fibres! Instead, invest in some advice from a masters qualified nutritionist or dietitian who has experience in managing IBS.

Blood Sugar and Glycemic Control

Fibre can improve your blood sugar and glycemic control - but once again, only if you consume the right types.

The beneficial fibres in this case are all of the soluble viscous/gel-forming fibres, and their beneficial effect takes place in the small intestine:

1. Soluble Fibres that are thickening/gel-forming + Non-Fermentable, like psyllium; and

2. Soluble Fibres that are thickening/gel-forming + Fermentable like β-glucans (oats, barley, mushrooms), pectin (apples, citrus peels, beetroot, peaches, cherries and pears), guar, glucomannan and xanthan gum.

All of these fibres thicken into a bulky, gel-like substance once we consume them. This bulky gel thickens the chyme (ie, the liquid mix of partially digested food and digestive enzymes/juices) in our small intestine. The thick gelled chyme slows the access of our digestive enzymes to the food we have consumed (slowing down the rate at which our food is broken down into its component nutrients), plus the thickened chyme also slows down the rate at which the nutrients from our food (like glucose and fatty acids) are absorbed into our bloodstream via the villi that line our small intestine.

So in terms of the glycemic impact of the foods we eat: when we consume meals that contain the thickening/gel-forming soluble fibres like oats or psyllium, it takes longer for our body to break the carbs in our meal down into glucose, and it also takes longer for that glucose to be absorbed into our bloodstream. The result is a slower, less dramatic rise in postprandial (post-meal) blood sugar. This helps us to avoid dramatic spikes in blood sugar when we eat, and also means we are less likely to experience the resultant large spikes in insulin that can cause reactive hypoglycaemia (low blood sugar), and which over time can lead to insulin resistance and place us at risk of Type 2 Diabetes.

But that’s not the only way these fibres help us with our glycemic control. The thickened/gelled chyme in our small intestine can also trigger a feedback mechanism in the small intestine called the “illium brake phenomenon”. Let me explain: Usually, most food digestion and nutrient absorbtion takes place in the first section of our small intestine, the duodenum. But when gel-forming fibre thickens up the chyme that moves through our small intestine, nutrient absorbtion will also take place further along along the length of our small intestine, including in its lower reaches, known as the distal ilium. And when nutrients are absorbed in the distal ilium, where they aren’t usually absorbed, the “ilium brake” is triggered. Think of it as an intestinal “go slow” mechanism. It slows the transit of food through our digestive system and stimulates release of peptide YY (PYY) and glucagon-like peptide-1 (GLP-1), which in turn decreases appetite, increases insulin secretion, decreases glucagon secretion (a peptide that stimulates glucose production in the liver), increases pancreatic β-cell growth (cells that produce insulin), improves insulin production and sensitivity.

So if you are insulin resistant, experience hypoglycaemic (low blood sugar) episodes or have been diagnosed with Type 2 Diabetes, definitely consider adding foods rich in these amazing thickening/gel-forming fibres like oats, barley or psyllium to your diet!

Cholesterol Lowering

Fibre can lower your cholesterol. But only certain types of fibre can do this, while others won’t have much or any effect at all.

The same fibres that help with glycemic control also help to lower cholesterol, which is awesome because people who have issues with their blood sugar often also have issues with their cholesterol.

So once again, the beneficial fibres in this case are all of the soluble thickening/gel-forming fibres, and their beneficial effect takes place in the small intestine:

1. Soluble Fibres that are thickening/gel-forming + Non-Fermentable, like psyllium; and

2. Soluble Fibres that are thickening/gel-forming + Fermentable like β-glucans (oats, barley, mushrooms), pectin (apples, citrus peels, beetroot, peaches, cherries and pears), guar, glucomannan and xanthan gum.

The primary mechanism by which the viscous, gel-forming fibres can lower cholesterol is by trapping and eliminating bile, which would otherwise be reabsorbed and recycled many times over. Confused? No worries. Let me explain…

Normally, after we eat a meal, our liver excretes bile into our duodenum (the first stage of our small intestine). The purpose of the bile is to help us digest the fats in our meal, by emulsifying large fat particles into many small particles that are small enough for digestion by our lipase (fat digesting) enzymes, which will in turn allow absorption of fatty acids into our bloodstream via the vili that line our small intestine.

This bile that is secreted into the first stage of our small intestine (the duodenum), does its job emulsifying the fats from our meal and then once it reaches the last stage of our small intestine (the ilium), the bile is reabsorbed and recycled back to our liver for re-deployment. This can happen over and over again, each time we eat a meal.

And here’s where the thickening/gel-forming fibres like oats and psyllium work their cholesterol-lowering magic! We saw above that these kinds of gelling fibres thicken up the chyme in our stomach and small intestine. Well, when our chyme is thickened by these kinds of gelling fibres, it “traps” the bile within the thickened chyme, which hampers the re-uptake of bile from our distal ilium. So instead of being recycled back to the liver for redeployment, that bile is trapped, carried away, and eliminated in your stool.

Your liver notices this lower bile re-uptake, and in response to less bile availability, it gets to work to make more bile. And this is where cholesterol comes in - our liver uses LDL cholesterol, which it pulls in from your bloodstream(!), to make more bile. In technical terms, the cells in our liver (hepatocytes) activate their LDL cholesterol receptors to bring in LDL cholesterol from your bloodstream and into your liver. The result is that the amount of LDL cholesterol in your bloodstream reduces, your total cholesterol lowers (due to the lowered LDL-C), but (good news!) your HDL (aka healthy) cholesterol levels remain unaffected. So your ratio of LDL:HDL cholesterol improves too. Awesome, right?!?!

Remember, it is the viscous, gel-forming characteristic of fibre that is critical to this cholesterol-lowering effect. Insoluble fibres like wheat bran or non-gelling soluble fibres like inulin won’t get the job done.

So if your LDL cholesterol reading is on the high side, definitely consider adding oats, barley or psyllium to your diet (and make sure you keep your family doctor and cardiologist in the loop about this). In fact, B-glucans (oats, barley) and psyllium have US Food and Drug Administration approval for a “health claim” that they can reduce the risk of cardiovascular disease by lowering serum cholesterol.

Studies on psyllium have found a LDL cholesterol lowering effect of 6-24%, with greater reductions seen in people with higher LDL-C levels. Psyllium has been shown to be an effective “co-therapy” with cholesterol lowering medications like statins or bile acid sequesterants.

Satiety, Appetite Control and Weight Management

Is fibre a weight loss “magic bullet”? No (sorry). But if you are carrying extra weight, should you make a conscious effort to increase your consumption of an array of fibre-rich whole plant foods? Absolutely! Here’s why:

1. Whole plant foods that are rich in both insoluble fibre and the thickening/gel-forming fibres take up space in our stomach and small intestine. They physically fill us up more than refined, processed fibre-bereft foods.

2. Fibre-rich whole foods, especially those rich in insoluble fibre, make us work for our calories! We have to chew them, and for a lot longer than refined, processed foods. Think of how much time you spend chomping on a salad, or chewing you bowl of muesli. Then compare how fast you can wolf down a white bread sandwich or handful of potato chips! It can take up to 20 minutes for our body to register satiety and tell us we have had enough. Our satiety signal is a valuable biological mechanism, designed to keep us out of overnutrition. But the problem is that we can bolt down a LOT of food in 20 minutes, especially if it is highly refined and calorie dense! Fibre-rich wholefood meals that make us chew, show down the rate at which we eat and gives our body a chance to tell us when we have had enough to eat.

3. Whole, fibre-rich plant foods are generally a lot less calorie-dense than refined, processed foods. So if we fill up our plate at each meal with these foods, there is a pretty good chance we will fill ourselves up before we eat our way into overnutrition. In fact, one of my favourite ways to reduce calorie intake is to not by deprivation or cutting out foods, but by loading up on a rainbow of healthy, fibre-rich plant foods to “crowd out” the junk!

4. As described above, the thickening/gel-forming soluble fibre foods like oats and barley thicken up the chyme in our stomach and small intestine, delaying release of glucose and fatty acids into our bloodstream, and then triggers the “ileal brake” cascade which include release of apetite-decreasing glucagon-like peptide-1.

So, include a mix of insoluble plus thickening/gelling soluble fibres in your diet to increase satiety, help keep you out of overnutrition and maintain a healthy body composition.

Cardiovascular Disease (CVD) Risk

Fibre consumption is consistently associated with lower incidence of CVD and CVD mortality. This has been attributed to a combination of all of the above factors (improved glycemic control, cholesterol lowering, and appetite management/weight regulation) plus the fact that fibre consumption is also associated with lowering blood pressure (one of the biggest risk factors for heart attack and stroke). But once again, remember that it is the viscous/gelling soluble fibres that deliver these benefits.

The fermentable soluble fibres feed the healthy microbes in our large intestine

The tiny bacteria in your large intestine are your secret health weapon. Or they can be, if you feed them right! And that’s where the fermentable soluble fibres come in. Fermentable fibres are “prebiotics”, aka food for “probiotics” (the healthy microbes that live in our large intestine).

The tiny “good guy” microbes that live in our large intestine are very picky eaters. They only like the super healthy stuff like fermentable soluble fibres and the polyphenols found in colourful plant foods.

But the problem is, we tend not to send through enough of this good suff. Instead, so many of us chow down on the standard Western diet which is low in fibre and high in calories, fat, refined carbs, salt and sugar. Not only do these fibre-bereft processed foods not feed our “good guy” microbes, much worse, they can actually feed and grow the less-than-ideal microbes in our gut like e.coli and other gram negative bacteria. The end result is an imbalance in the bacteria in our large intestine. People eating these diets have been found to have low diversity of bacterial species in their bowel, with less of the “good guys”. Scientists refer to this as “dysbiosis”.

And here’s why we should make an effort to consume more fermentable/prebiotic fibres:

The “good guy” bacteria in our large intestine are involved in vitamin synthesis, immune function, appetite regulation, and they can even protect us against cancer! How? When the “good guy” microbes in our large intestine consume fermentable fibres, they excrete a variety of short-chain fatty acids (SCFA’s): mainly acetic, propionic and butyric acids. These SCFA’s are a vital source of fuel for our colonocytes (the cells that line our large intestine), keeping them functioning at their best, making them less likely to become abnormal or cancerous.

Excretion of SCFA’s also lowers to pH in our large intestine, and that’s a good thing. The less-than-ideal microbes in our large intestine like e.coli and other gram negative bacteria prefer a higher pH, whereas our “good guy” bacteria like a lower pH. So giving the good guys the food they need, helps them create the environment they need, which in turn discourages proliferation of unhealthy microbes.

But the benefits of SCFA’s aren’t confined to our bowel. SCFA’s also serve as important signalling molecules in a number of biochemical systems and pathways throughout the body. For example, they can stimulate the release of the neurotransmitter serotonin (which can influence mood, sleep and memory). Butyric and propionic acids have an anti-inflammatory effect by inhibiting production of inflammatory cytokines by our immune cells.

Protection against Colon Cancer

In the early days of fibre research, scientists observed lower rates of colon/bowel cancer in populations whose diets were high in fibre-rich whole plant foods, compared with those consuming the standard, highly-processed Western diet. Those early observational studies have been confirmed many times over, and scientists have uncovered the following mechanisms:

Fibre, especially insoluble fibre and the soluble thickening/gel-forming fibres, bulk up our stool, dilute any toxins or carcinogens that may be present. These fibres also speed the transit of our stool through our bowel. The combined effect of diluting toxins in our stool and a faster transit time through our bowel means that our bowel wall (where colon/bowel cancer can grow) has much less exposure to potential carcinogenic (cancer-causing) substances.

But that’s only part of the story. Fermantable fibres like resistant starch (ie, “carby” foods that have been cooked and then cooled) or the beta glucan fibres in oats serve as food for the healthy “good guy” microbes that reside in our large intestine. These “good guy” microbes consume these fermentable fibres and then excrete short chain fatty acids (SCFA’s). These SCFA’s provide much-needed energy to our colonocytes, the cells which line our large intestine. Butyric acid in particular plays an important anti-cancer role by helping colonocytes, to perform important functions like triggering apoptosis (programmed cell death) of abnormal cells before they can become cancerous. Yep, with the help of our “good guy” bacteria, consuming fermentable fibre can help us stop colon/bowel cancer before it starts!

So, for bowel cancer prevention, aim for a mix of insoluble fibre, thickening/gel-forming soluble fibre and fermentable fibres. Eat a rainbow of fruit and vegetables, whole, unprocessed grains and brans, legumes, nuts and seeds, consider adding in some psyllium, wheat bran and/or oat bran, and give your “carby” foods like potatoes, rice and pasta the Resistant Starch treatment by cooking them and then cooling them overnight!

Inflammation and immunity

The fermentable/prebiotic fibres have been shown in studies to have a beneficial effect on inflammation biomarkers, and our immune system. This is because the SCFA’s excreted by the “good guy” bacteria in our large intestine increase phagocytosis, NK (natural killer) cell activity, promote the function and number of our regulatory T cells, help to maintain gut barrier function, regulate the production of anti-inflammatory cytokine interleukin-10, decreases in the production of proinflammatory cytokines, and support immune cell populations.

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Whole Food v Fibre Supplements

We can consume fibre:

1. In whole-food form: in whole unprocessed grains, legumes, fruit, vegetables, nuts and seeds).

2. As a supplement: There are many different types of fibre supplements;

3. As an additive to processed and packaged foods.

I strongly recommend you consume your fibre in wholefood form wherever you can, and if you are consciously seeking to boost your fibre intake, think “food first!”. That’s because:

1. Most plant foods contain more than one type of fibre, and different fibres can yield synergistic health benefits (more on that below); and

2. Fibre-rich, whole plant foods like fruit, vegetables, whole grains, legumes, nuts and seeds come with an amazing “travelling companions” like vitamins, minerals and super-healthy phytonutrients. Science is increasingly uncovering an array of amazing health benefits - for an example, check out THIS POST on one variety of phytonutrient, the anthocyanins found in purple plant foods. One family of phytonutrients, the polyphenols, are also a preferred food source for our “good guy” gut bacteria.

Eat all of the different types of fibre!

In Part 1 of this three-part series, we learned that there are actually FIVE different classes of fibre, and that each of these five classes behaves differently in the human body, and delivers its own unique set of health benefits!

Don’t miss out on a fantastic health benefit - make sure you diet includes all of the five different types of fibre. How do you do this? Put down the processed food and enjoy a wholefood diet that is predominately made up of a wide variety of all types of plant foods - vegetables, fruit, nuts, seeds, whole grains, pulses and legumes. Go for as much variety as possible in all the colours of the rainbow.

Consuming different types of fibre together can yield synergistic benefits

For example, fermentable/prebiotic fibres like resistant starch are usually quickly fermented in the proximal colon (ie. the start of our large intestine). This means that most of the excretion of the beneficial short chain fatty acids produced by fermentation of these prebiotic fibres is concentrated there, and they aren’t necessarily distributed all the way through our large intestine.

But when we combine insoluble fibre with easily fermented probiotic fibres like resistant starch (from cooked-then-cooled carbs), the release of SCFA’s and the pH lowering effect gets spread all the way through your large intestne. This means more healthy bacteria, and greater excretion of beneficial short chain fatty acids in your distal colon (on your left side) which is where abnormal cells and tumours are more likely to be found.

Make sure you check out Part 3 in this three-part series for my top tips for increasing dietary fibre intake!

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