The Importance of Fibre in the Diet

by Matt Durkin
MSc Nutrition Specialist
20/04/2018

Following on from our previous article that looked at the importance of protein, this article is going to tackle another important aspect of the diet: fibre. Once called roughage, fibre is another nutrient that we know we need, but don’t necessarily know a whole lot about.

What is Fibre?

We are all likely to have seen the word ‘fibre’ on food packaging, and heard of foods claiming they contain it in high amounts, but what actually is fibre? In short, fibre is actually a type of carbohydrate. Unlike other carbohydrates, however, fibre does not get digested in our small intestine and therefore does not enter the bloodstream.

It is important to note that there are actually two different types of fibre: soluble and insoluble. As their names suggest, their different actions relate to their interaction with the water in our digestive system. Soluble fibre mixes with water and forms a gel-like substance in the stomach which slows digestion.

In contrast, insoluble fibre does not mix with water, and passes through the intestines in relatively the same form, speeding up the rate of digestion.  To have a good balance is important for optimal health, and therefore we need to include foods in our diet that are rich in both types. We will find out more on this later in the article.

Why is Fibre Important?

Fibre has many proven benefits to health, which is why we are encouraged to include more in our everyday diet. Firstly, we will start by looking at the benefit that most people will know, which is the impact fibre has on our digestive health.

Digestion

Dietary fibre helps our digestive system as it increases the weight and size of our stools which makes them easier to pass, decreasing the risk of constipation.  Having loose or watery stools is often a sign that you have a diet low in fibre and need to include more fibre rich foods. People who have a fibre rich eating plan have also been shown to be less likely to suffer from haemorrhoids, ulcerative colitis, and bowel cancer, due to its benefits to food transit.

It’s only in the last 20 years however that scientists have discovered another mechanism by which fibre boosts digestive health. In our gut there exist trillions of bacteria that make up something experts call ‘the microbiome’. Although research into gut bacteria is still in its infancy, there are some very exciting findings in relation to digestive health, but also the protection from metabolic and cardiovascular diseases and various types of cancer. For this reason, the gut is often referred to as the ‘forgotten organ’.

We are all likely to have heard of probiotics which introduce new strands of ‘good’ bacteria into the gut, with many of us starting the morning with a probiotic drink. Lesser-known, however, is prebiotics, which acts as fuel for the ‘good’ bacteria, helping them to flourish and subsequently benefitting our health. Certain types of soluble fibres such as inulin, oligofructose and fructooligosaccharide (FOS) are the ones that scientists have found to exert a powerful impact on our gut bacteria and therefore our health.

Cardiovascular Health

The cardiovascular system comprises the intricate workings of the heart, blood and vessels that ensure all our cells receive the oxygen and nutrients we need to survive. In short, taking care of this system is crucial. Unfortunately, we could be doing a lot better, as Cardiovascular Disease (CVD) is the biggest cause of death in the UK and the rest of the world.  

One area where we could improve the health of our heart is by increasing the amount of fibre in our diet, as after all, the research has consistently shown that those with a high fibre diet typically have a lower risk of developing CVD and dying prematurely.
Cardiovascular disease can present itself through numerous pathologies, be it abnormal cholesterol and sugar levels, blood pressure, or high amounts of visceral body fat – the fat that surrounds the vital organs.

Cholesterol

The research has consistently shown that a high fibre diet can improve a number of the health parameters mentioned above. Firstly, fibre is effective at reducing LDL cholesterol, which is often referred to as the ‘bad’ cholesterol. Although the effect is modest, Heart UK states that reducing LDL cholesterol by as little as 5% would reduce thousands of cases of CVD.

Blood Sugar

High fibre foods are also commonly known to provide ‘slow-releasing energy’. They do this by lowering the glycaemic index (GI) of a meal, which is the way scientist’s measure how quickly a meal increases blood sugar. Foods that have a high GI such as jelly sweets increase blood sugar rapidly, but this is often short-lived, as lulls in energy soon occur. This is in contrast to low GI foods such as whole grains, which ensure a steady influx of glucose into the blood.

Furthermore, foods that have a high GI lead to the release of insulin, and often the body secretes more of this hormone than it actually needs. Insulin works by shuttling glucose from the blood into the cells and is perfectly healthy. However, excessive insulin can cause the cells becoming resistant – something that is a major cause of type 2 diabetes. As diabetes accelerates CVD progression, fibre has a protective effect through this mechanism.

Blood Pressure

High blood pressure, also known as hypertension, is a massively common issue that not only increases the risk of heart attacks and strokes but kidney and eye issues as well. A diet that is rich in fibre has been shown to reduce blood pressure in both healthy individuals and those diagnosed with hypertension.

A meta-analysis of randomised control trials conducted in 2005 found that a high fibre diet can decrease both systolic and diastolic blood pressure. A meta-analysis is widely accepted to be the gold standard of scientific evidence as it collates the results of numerous studies to provide a valid answer to a specific question. As hypertension is thought to affect 1 in 3 adults, and is the cause of almost three-quarters of all strokes, reducing blood pressure is high up on the agendas of national health institutions.

Obesity

Obesity is a leading cause of CVD independent of the negative effects it can have on CVD risk factors such as blood cholesterol, sugar and pressure.  Although there are many factors involved in the cause of obesity, they all lead to an energy imbalance. So, we need to primarily focus on being active and controlling our calorie intake.

One of the best ways to control calorie intake and therefore bodyweight is to consume foods that provide satiety - making us feel full. As high fibre foods increase bulk in the stomach, lower the GI and have a slow transit time in the gut, they exert positive benefits on the appetite hormones. Research is also pretty clear that those who have a high fibre diet eat fewer calories on a day-to-day basis and therefore have lower levels of body fat.

Nutrient Density

High fibre foods are typically healthy not only because of their fibre content but due to their nutrient density also. Vitamins and minerals are known as micronutrients seeing as they are only needed in small amounts. Although a relatively small amount of the diet, they have an almost inexhaustible number of roles, from metabolism and energy levels to eye health, cognitive function and immunity. So typically, people with high fibre diets tend to be generally healthier as they naturally obtain sufficient vitamins and minerals daily.

Refined grains such as white bread, white rice and white pasta are categorised by the removal of fibre. However, the removal of fibre also sees the removal of the vitamins and minerals. So refined grains are not only worse for health as they rapidly increase blood sugar levels, they also are bereft of essential nutrients.

How Much Fibre Should We Eat?

Throughout this article there have been a number of references to a high fibre diet, so now it is time to quantify this. In the UK, the old fibre recommendation used to be 21g per day. However, the recent evidence has suggested that the health benefits are achieved with a higher intake. Subsequently, the Department of Health now recommends we consume 30g per day.

This is bad news for the UK population, however, as failure to meet the old recommendation was well-publicised, let alone the updated one. Government statistics have shown that on average men only achieve an intake of 17g per day, with women slightly less at 16g. As a result of this, we could do with increasing our knowledge with regards to good sources of fibre and also pay attention to nutrition labels when doing our food shop.  

It is important to note that increasing fibre intake too quickly can cause symptoms such as stomach cramps and excessive wind, so it is important to gradually increase fibre intake to give the digestive system chance to adapt.

What Are Good Sources of Fibre?

There are various types of food groups and sources that provide fibre, be it soluble or insoluble. Below is a list providing some good examples of fibre sources:

Wholegrains & Cereals

• Wholemeal pasta: 80g of uncooked provides 7g
• Brown rice: 80g of uncooked provides 3g
• Wholemeal bread: 1 slice provides 2.5g
• Oats: a 50g serving provides 5.5g
• Bran flakes: 30g serving provides 5g

Fruits

• Banana: 1 medium provides 2.3g
• Avocado: half a medium fruit provides 6g
• Raspberries: 100g provides 6.5g
• Pears: 1 medium provides 5.5g

Vegetables

• Broccoli: 100g portion provides 2.7g
• Carrots: 100g portion provides 2.8g
• Green beans: 100g portion provides 3.4g
• Parsnips: 100g portion provides 5g

Legumes

• Kidney beans: 50g portion provides 12g
• Chickpeas: 50g portion provides 8.5g
• Lentils: per cup (cooked) provides 15g

Nuts & Seeds

• Almonds: 30g providing 3.6g
• Walnuts: 30g provides 2.8g
• Pumpkin seeds: 30g provides 5.2g.

Putting This Together

Now we have discovered some of the best sources of fibre, let’s now have a look at what a day’s eating could look like to achieve the recommended 30g.

Breakfast (8g of fibre)
A bowl of porridge with a small handful of raspberries.

Lunch (14g of fibre)
Chicken & avocado salad sandwich on wholemeal bread, a handful of mixed nuts and a medium pear.

Evening Meal (9g of fibre)
A fillet of salmon, with a portion of new potatoes and a side of green beans, carrots and broccoli.

Supplements

Although the above example shows that meeting the recommended fibre intake is achievable, many of us are still falling well short. Given fibres importance, many are now utilising the convenience of high-quality supplements to ensure they reap the plethora of fibre-related health benefits.

One supplement that has grown in popularity in recent years thanks to attention from media outlets and the scientific community is inulin. Inulin naturally occurs in appreciable amounts in onions, garlic and artichokes, and is now increasingly being used in fibre supplements.
Inulin is very popular due to its versatility. Inulin powder is naturally sweet, which means it is being used as a healthy replacement for sugar in foods and beverages. It is also 90% fibre by weight, meaning a teaspoon of inulin power provides 4.5g of pure fibre.

Summary

Hopefully this article has outlined why fibre is important in our diet and has encouraged people to be mindful of their intake. Let us now sum up the key points of this article in the take-home messages:

Fibre is a type of carbohydrate that is neither digested nor absorbed in the small intestine. There are two types of fibre known as soluble and insoluble which have slightly different roles.

It is well-known that fibre is very beneficial for digestion and gut health, but it is also protective against bowel cancer and various facets of cardiovascular health. Similarly, fibre is satiating which benefits appetite responses and subsequently bodyweight.

Fibre-rich foods also tend to contain high levels of micronutrients, so focussing on foods high in fibre will ensure sufficient intake of a wide range of vitamins and minerals

The current fibre recommendation by the Department of Health is 30g per day. Unfortunately, as a nation we are falling well short, with the average intake being under 18g per day.

Whole grains, cereals, fruits, vegetables, legumes, nuts and seeds are the best sources of fibre and should be incorporated daily.

As many find it difficult to achieve 30g per day through food alone, high-quality fibre supplements such as inulin powder have become a popular and convenient way to ensure any dietary shortcomings are rectified.  

Sources
https://www.ncbi.nlm.nih.gov/pubmed/18842802/
http://www.bmj.com/content/347/bmj.f6879
https://heartuk.org.uk/press/press-kit/key-facts-figures
https://www.nature.com/articles/1601283
https://www.ncbi.nlm.nih.gov/pubmed/18237578
https://www.ncbi.nlm.nih.gov/pubmed/15668359
https://www.ncbi.nlm.nih.gov/pubmed/11497328
https://www.ncbi.nlm.nih.gov/pubmed/18685505
https://www.ncbi.nlm.nih.gov/pubmed/23609775

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