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Dietary Fibre

What is dietary fibre? Why and how much fibre do we need? What are the best sources of dietary fibre?

We all know that a balanced diet is healthier and provides us with all the nutrients we need, but usually, we only talk about the amount of protein, fat and carbohydrates we need. Dietary Fibre is less often talked about because it has no nutrients – but fibre is also vital for our bodies.

 

What is dietary fibre?

In the past, dietary fibre (also known as roughage or bulk) was defined as complex carbohydrates found only in plant products such as cereals, whole grains, fruits, vegetables, legumes, nuts, seeds and mushrooms.

It was thought that fibre is not broken down and absorbed by our bodies because our digestive system does not secrete enzymes to break it down.

However.

Recently, scientists have discovered that some digestible substances also share properties with dietary fibre, so it is now harder to define.

 

Although fibre is not used as fuel by the body, it has a significant impact on our well-being and health.

For example, it slows digestion, prevents blood sugar spikes after meals, promotes healthy bacteria colonies and helps to regulate weight and avoid constipation. There are many subtypes of soluble and insoluble fibres, some naturally occurring in plant-based foods, while others are synthetically produced.

 

The nutritional value of foods usually does not indicate the amount of fibre because it does not contain any nutrients.

 

Types of dietary fibre

Two types of fibre are typically distinguished:

  1. Soluble fibre – a food source for gut bacteria, which are important for immunity and helps regulate sleep, appetite and mood. Good sources of water-soluble fibre are oatmeal, nuts, beans, lentils, apples, citrus fruits and blueberries.
  2. Insoluble fibre – improves digestive function (‘cleans’ the gut, thus promoting both nutrient absorption and detoxification). Helps to prevent constipation and/or irregular bowel movements. Good sources of water-insoluble fibre are whole-grain products (e.g. wholemeal bread, brown rice, etc.), bran, nuts, legumes and vegetables (e.g. carrots, cabbage, cucumbers, tomatoes, etc.).
 

However, fibre can also be described in other ways, for instance:

  1. Fermentable fibre – a viscous and gelatinous mass that serves as food for gut bacteria to break down and ferment.
  2. Non-fermentable fibre (which is not broken down by bacteria), passes intact into the large intestine and increases the volume and weight of the stool to make it easier to pass.
 

The US National Academy of Medicine defines fibre as:

  1. Dietary fibre (indigestible carbohydrates and lignans) that occurs naturally in plants.
  2. Functional fibre either plant-derived or synthetically produced, is not digestible but has a beneficial effect on human health.
 

Naturally occurring plant fibres

  • Cellulose, hemicellulose – insoluble fibres found in cereal grains and many fruits and vegetables. These fibres absorb water and increase stool volume, which in turn promotes defecation.
  • Lignins – insoluble fibre found in wheat and corn bran, nuts, flaxseeds, vegetables and unripe bananas. Lignins promote mucus secretion in the large intestine, increase stool volume and promote defecation.
  • Beta-glucans – soluble, highly fermentable fibres found in oats and barley and being fermented in the small intestine. Acts, as a prebiotic. They may help normalise blood glucose and cholesterol levels and increase stool volume but have no laxative effect.
  • Guar gum – a soluble, fermentable fibre extracted from seeds. It has a viscous, jelly-like consistency and is often added to foods as a thickening agent. Guar gum may help normalize blood sugar and cholesterol levels.
  • Inulin, oligofructose, oligosaccharides, fructooligosaccharides – soluble fermentable fibres found in onions, chicory root, asparagus and Jerusalem artichokes. May act as prebiotics and help normalize blood glucose levels. People with irritable bowel syndrome may have an increased sensitivity to these fibres, which can cause bloating or an upset stomach. May have a laxative effect.
  • Pectins – soluble, easily fermentable fibres found in apples, berries and other fruits. Because of their gelling properties, they can slow digestion and help normalise blood sugar and cholesterol levels. Minimal bloating and laxative effect.
  • Resistant starch – a soluble, fermentable fibre found in legumes, unripe bananas, cooked and cooled pasta and potatoes. Help normalize blood sugar and cholesterol levels. Acts as a prebiotic. Increases stool volume but has minimal laxative effect.
 

Industrially produced functional fibres some of which are extracted from natural plants

  • Psyllium – a soluble, viscous, non-fermentable fibre obtained from psyllium seeds. Psyllium may help normalise blood sugar and cholesterol levels. Psyllium retains water, softens and increases stool volume and has a laxative effect (found in many over-the-counter laxatives).
  • Polydextrose and polyols – soluble fibres composed of glucose and sorbitol (sugar alcohol). Minimal effect on blood sugar and cholesterol levels. Has a mild laxative effect. Used as a food additive – as a sweetener, to improve texture, retain moisture or increase fibre content.
  • Inulin, oligosaccharides, pectins, resistant starch and guar gum are also produced industrially by isolation from plants to make a fibre concentrate added to foods or supplements.
 

Why do we need dietary fibre?

Dietary fibre performs many functions in our bodies, to name just the most important:

  • Contribute to the functioning of the digestive system (facilitating the absorption of nutrients, and reducing the risk of constipation).
  • “Feed” the intestinal microbiota, which produces natural antibacterial agents and regulates our body’s immune and allergic reactions.
  • Helps regulate blood sugar and cholesterol levels (read more about cholesterol HERE).
  • Promotes the body’s cleansing of harmful substances;
  • Reduces hunger (slows digestion) thus helping to avoid overeating and control the body weight.
 

Several studies show that fibre intake reduces the risk of death (from any cause). In one study, people with a higher fibre intake had a 23% lower risk of death compared to those with a low fibre intake.  This relationship was most pronounced when the fibre was obtained from cereals and vegetables rather than fruit.

An analysis of nearly 250 studies confirms that high fibre intake from vegetables, fruits and whole grains can reduce the risk of death from cardiovascular disease and cancer. People who consumed more fibre had a 16% to 24% lower risk of death from heart disease, stroke, type 2 diabetes, and/or colon cancer than those who consumed little fibre. A meta-analysis of these studies also concluded that more fibre is better. For every additional 8 grams of fibre consumed per day, the risk of each disease fell by a further 5% to 27%. The risk reduction was greatest when daily fibre intake was between 25 and 29 grams per day.

Research has also shown that fibre, especially found in fruits, grains and vegetables, protects against diverticulitis.

 

How much dietary fibre do we need?

The recommended daily intake according to age and gender is as follows:

Age

Men

Women

0 to 12 months

Not determined

Not determined

1 to 3 years

19 g/day

19 g/day

4 to 8 years

25 g/day

25 g/day

9 to 13 years

31 g/day

26 g/day

14 to 18 years

38 g/day

26 g/day

19 to 50 years

38 g/day

25 g/day

51 to 70 years

30 g/day

21 g/day

> 70 years

30 g/day

21 g/day

Pregnant women 18 to 50 years old

 

28 g/day

Breastfeeding from 18 to 50 years old

 

29 g/day

 

Or about 14 grams of dietary fibre for every 1000 calories consumed.

 

The best way to get dietary fibre is through whole-grain products and vegetables. Dietary fibre supplements are not recommended because although many fibre supplements are fortified with vitamins and minerals, they are processed and semi-synthetic products.

 

Fibre supplements are recommended for specific health problems such as constipation, diarrhoea or irritable bowel syndrome. Consult your doctor before taking fibre supplements.

 

How to boost fibre intake?

You definitely shouldn’t change your diet drastically and rapidly, as suddenly switching to a fibre-rich diet can cause unpleasant side effects, for example, bloating and flatulence. Raise the amount of fibre in your diet gradually to allow the bacteria in your digestive system to adapt to the change.

Despite the benefits of fibre on our health described above, I recommend not to overdo it. Excessive fibre intake (more than 70 g per day) can lead to cramping abdominal pain and vitamin and mineral deficiencies (especially calcium, magnesium and zinc), as fibre can limit their absorption. The risk of intestinal blockage is also increased – so more fibre intake means drinking more water. Read more about the importance of water in our bodies HERE.

 

How to increase your fibre intake:

  • Choose a fibre-rich breakfast cereal (5 g or more fibre per portion). For example, wholemeal porridge, or add a few tablespoons of raw wheat bran to your favourite breakfast.
  • Eat whole fruits instead of drinking juices.
  • Snack on crunchy fresh vegetables or a handful of almonds instead of crisps and crackers.
  • Switch to wholemeal products, for example – look for bread with wholemeal flour as the first ingredient on the label. Try brown or wild rice, wholemeal pasta, bulgur, etc.
  • Replace white rice, bread and pasta with minimally processed brown rice and other whole grains such as barley, millet, amaranth, farro.
  • When baking pastries, add 50% wholemeal flour to white flour or use wholemeal flour only. When baking muffins, cakes or biscuits, add chopped bran or raw oat flakes.
  • Beans, peas and lentils are excellent sources of fibre. Add canned beans to soup or salads. Or make a nacho with black beans, fresh vegetables, wholemeal tortilla and salsa.
  • Replace meat with beans or other legumes in soups and stews two to three times a week.
  • Add high-fibre foods to your current meals, e.g. add 1-2 tablespoons of almonds, ground linseed or chia seeds to breakfast cereals.
  • Use fresh fruit, raw vegetables, low-fat popcorn, etc. for snacks. A handful of nuts or dried fruit is also a healthy high-fibre snack, but be aware that nuts and dried fruits are also high in calories.
 

In other words, eat more fruits, vegetables, legumes, nuts and seeds – they are rich in fibre, as well as, vitamins and minerals.

Here’s an example of how easy it is to get 40 g of fibre a day:

 

Food

Amount of fibre

Breakfast

25 blueberries

1 cup of cooked oatmeal

1 g

4 g

Lunch

1/2 cup cooked brown rice

1/2 cup cooked split peas

1/2 cup cooked broccoli

1.5 g

8.5 g

3 g

Dinner

1 avocado

2 slices of whole wheat bread

13.5 g

4 g

A snack

1 medium pear

5.5 g

In total:

41 g

 

The best sources of dietary fibre

The optimal fibre content is 6 grams or more for cereals and muesli, 3 grams or more for bread and bakery products and 4 grams or more for pasta. Wholegrain products should contain at least 1 gram of fibre per 10 grams of carbohydrate.

Remember that product names can be misleading – “Multigrain” or “12-grain”, “wholemeal”, etc., do not mean that they are wholemeal.

 

Fibre content of common foods

Fruits

Portion

Total fiber content

Avocado

1 cup

10.0 g

Raspberries

1 cup

8.0 g

Pear

1 medium

5.5 g

Apple with peel

1 medium

4.5 g

Banana

1 medium

3.0 g

Orange

1 medium

3.0 g

Strawberry

1 cup

3.0 g

Blackberries

100 g

5.3 g

Blueberries

100 g

2.4 g

Vegetables

  

Green peas, cooked

1 cup

9.0 g

Artichokes, raw

1 medium

6.9 g

Broccoli, cooked

1 cup, chopped

5.0 g

Turnip leaves, cooked

1 cup

5.0 g

Brussels sprouts, cooked

1 cup

4.0 g

Potatoes, with peel, fried

1 medium

4.0 g

Sweet potatoes, boiled (without skin)

1 medium

3.8 g

Sweet corn, boiled

1 cup

3.5 g

Cauliflowers, raw

1 cup, chopped

2.0 g

Carrots, raw

1 medium

1.5 g

Cabbage, raw

100 g

2.5 g

Beetroot, raw

100 g

2.8 g

Spinach, uncooked

100 g

2.2 g

Tomatoes, raw

100 g

1.2 g

Grains

  

Spaghetti, whole grain, cooked

1 cup

6.0 g

Barley, pearl barley, cooked

1 cup

6.0 g

Bran flakes

3/4 cup

5.5 g

Quinoa, boiled

1 cup

5.0 g

Oatmeal, quick to cook, boiled

1 cup

5.0 g

Popcorn, inflated

3 glasses

3.5 g

Brown rice, cooked

1 cup

3.5 g

Bread, whole grains

1 slice

2.0 g

Bread, rye

1 slice

2.0 g

Legumes, nuts and seeds

  

Split peas, cooked

1 cup

16.0 g

Lentils, cooked

1 cup

15.5 g

Black beans, boiled

1 cup

15.0 g

Beans, canned

1 cup

10.0 g

Chia seeds

28.35 g

10.0 g

Quinoa, boiled

1 cup

6.2 g

Almonds

28.35 g

(23 nuts)

3.5 g

Pistachios

28.35 g

(49 nuts)

3.0 g

Sunflower seeds

28.35 g

3.0 g

Coconut, fresh

100 g

9.0 g

Walnuts

100 g

6.7 g

Pumpkin seeds

100 g

6.5 g

Source: USDA. Rounded to the nearest 0,5 g (28.3495 g = 1 ounce).

 

Key takeaways

Fruits, vegetables and grains tend to be rich in different types of fibre, but in variable amounts.

Therefore to get the maximum benefit from dietary fibre we need to add variety to our menus.

In other words – do not focus too much on a particular fibre because of its specific effects, but increase the variety of plant-based foods in your diet.

Peeling fruits and removing the outer skins of cereals reduces their fibre content. Therefore, it is better to choose unpeeled fruit and whole-grain products.

Read HERE how a healthy diet affects your mood.

 

Eat tasty, eat balanced, move and – be healthy!

DEFINITIONS OF DIETARY FIBER

Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids

Fiber: Resistant Starch and Oligosaccharides

A Randomized Placebo-Controlled Clinical Trial to Evaluate the Medium-Term Effects of Oat Fibers on Human Health

Dietary Fiber, Atherosclerosis, and Cardiovascular Disease

Intake of dietary fiber, fruits, and vegetables, and risk of diverticulitis

Meta-Analysis of Usefulness of Psyllium Fiber as Adjuvant Antilipid Therapy to Enhance Cholesterol Lowering Efficacy of Statins

Food Ingredients That Inhibit Cholesterol Absorption

Dietary Fiber and Risk of Coronary Heart Disease

Diet and Lifestyle Factors and Risk of Atherosclerotic Cardiovascular Disease—A Prospective Cohort Study

Association Between Dietary Fiber and Lower Risk of All-Cause Mortality: A Meta-Analysis of Cohort Studies

Vegetable, Fruit, and Cereal Fiber Intake and Risk of Coronary Heart Disease Among Men

Carbohydrate Nutrition, Insulin Resistance, and the Prevalence of the Metabolic Syndrome in the Framingham Offspring Cohort

New strategies for the management of diverticular disease: insights for the clinician

Meat intake and risk of diverticulitis among men

Role of Dietary Habits in the Prevention of Diverticular Disease Complications: A Systematic Review

Source of dietary fibre and diverticular disease incidence: a prospective study of UK women

High intake of dietary fibre from fruit and vegetables reduces the risk of hospitalisation for diverticular disease

Nut, Corn, and Popcorn Consumption and the Incidence of Diverticular Disease

Chronic Constipation: Is a Nutritional Approach Reasonable?

Intake of Dietary Fruit, Vegetables, and Fiber and Risk of Colorectal Cancer According to Molecular Subtypes: A Pooled Analysis of 9 Studies

Different dietary fibre sources and risks of colorectal cancer and adenoma: a dose–response meta-analysis of prospective studies

Association between Dietary Fibre Intake and Colorectal Adenoma: A Systematic Review and Meta-Analysis

Association of whole grains intake and the risk of digestive tract cancer: a systematic review and meta-analysis

Fiber consumption and breast cancer incidence: A systematic review and meta-analysis of prospective studies

Adolescent alcohol, nuts, and fiber: combined effects on benign breast disease risk in young women

The journal of Nutrition

Dietary recommendations for dietary fibre intake

Dietary Reference Intakes

New Horizons for the Study of Dietary Fiber and Health: A Review

USDA

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