Fibre is one of the most overlooked nutrients in our diets today. Most people consume less than half of the recommended amounts, despite the big health benefits that come with a fibre-filled diet (McGill et al., 2015). Not only is fibre good for your gut, but it also plays a central role in keeping your heart healthy, too.
1. What is dietary fibre?
The term “Dietary Fibre” was first introduced in 1950, referring to plant cell wall materials which cannot be digested and absorbed in the gastro intestinal tract (Debnath et al., 2019). According to the American Association of Cereal Chemists (AACC, 2000), dietary fibre is the edible part of the plant or analogous carbohydrates that are resistant to digestion and adsorption in the human intestine with complete or partial fermentation in the large intestine (Rana et al., 2012). Dietary fibre includes polysaccharides, oligosaccharides, lignin and associated plant substances. It is mostly found in legumes, whole grain cereals, fruits and vegetables. Dietary fibre rich food products are generally associated with physiological actions in the small as well as large intestine thereby having important implications on human health (Rana et al., 2012). Intake of viscous dietary fibre may help in managing the low density lipoprotein cholesterol and glucose levels and induces short term satiety (Anderson et al., 2009). On the basis of energy intake, 30g/2000 kcal of dietary fibre is considered as safe for intake (NIN, 2020). American Dietetic Association has recommended 20-35g fibre per day for a healthy adult depending on the caloric intake. A total of 25gms of dietary fibre is recommended for women aged 19-50 years, 38gms for men aged 19-50 years, 21gms for women aged 51 years and older and 30gms for men aged 51 and older (Soliman, 2019).
2. Types of dietary fibre:
- Dietary fibre can be divided into two types based on its properties and its effects on the body. These two types are insoluble and soluble fibre. The difference is mainly based on solubility in water.
- Insoluble fibre:
Insoluble fibre also known as roughage includes cellulose, hemicellulose and lignin. They are found in foods such as wheat bran, whole grains, vegetables, nuts and seeds. Insoluble fibres do not dissolve in water and generally cannot withstand fermentation by the bacteria in the colon (Akbar et al., 2022). They absorb water and increase the intestinal bulk, and promotes laxation thus helps in preventing certain conditions such as constipation, haemorrhoids and diverticulitis (NIN, 2020).
Table 01: Types & properties of insoluble fibre
|Cellulose||Main structural component of plant cell wall. It is insoluble in concentrated alkali and soluble in concentrated acid|
|Hemicellulose||Cell wall polysaccharide soluble in dilute alkali|
|Lignin||Non-carbohydrate cell wall component that resists bacterial degradation|
Source: (Dhingra et al., 2012. Dietary fibre in foods: a review. Journal of food science and technology)
- Soluble fibre:
Soluble fibres, such as gums, pectin and mucilage dissolve in water and form a thick gel and are generally fermented by bacteria in the colon into gases and by-products such as short-chain fatty acids (Rana et al., 2012). They take up fluid in the gastrointestinal tract, thus forming a thick gummy substance. It also delays gastric emptying and intestinal transit time. Since soluble fibre has large water binding capacity it binds to kill acid and further helps to lower blood cholesterol levels and also helps in regulation of blood glucose levels by altering their absorption rates (NIN, 2020). Legumes, oats, and barley as well as vegetables such as carrots, broccoli, onion and fruits including bananas, berries, apples, and pears are good source of soluble fibre.
Table 02: Types & properties of soluble fibre
|Pectin||They are component of the cell wall, generally soluble in water and is gel forming.|
|Gums||Secreted at the site of plant injury and are generally used in food and pharmaceuticals.|
|Mucilage||Synthesized by plants and prevent desiccation of speed endosperm. Used in food industry, hydrophilic and stabilizer.|
Source: (Dhingra et al., 2012. Dietary fibre in foods: a review. Journal of food science and technology)
3.Sources of dietary fibre:
Plants foods are the only source of dietary fibre. Among them whole grains breads and cereals, fruits and vegetables, and dried beans and peas are good source of fibre. These foods provide both soluble as well as insoluble fibre.
Table 03: Dietary fibre of some Indian foods
|Food group||Food name||Dietary fibre (g/100g)|
|Cereals & Millets||Bajra||9.14||2.34|
|Oats (Dhingra et al., 2012)||6.5||3.8|
|Grain legumes||Bengal gram , whole||22.70||2.52|
|Green gram, whole||14.59||2.44|
|Soya bean. brown||16.56||5.00|
|Green leafy vegetables||Drumstick leaves||6.12||2.10|
|Tamarind leaves, tender||9.34||1.36|
|Roots & tubers||Carrot||2.81||1.37|
|Potato, brown skin||1.13||0.58|
|Condiments & spices||Chillies, red||26.55||4.60|
|Nuts & oilseeds||Almond||10.55||2.52|
|Gingelly seeds, black||13.57||3.59|
Source: Indian Food Composition Table (IFCT, 2017)
4. Role of dietary fibre:
- Insoluble fibre helps in maintaining bowel movements. They absorb water and softens the stools, thus preventing constipation. They add bulk to the stools thus preventing the formation of loose stools.
- A high-fibre diet prevents the formation or inflammation of haemorrhoids and diverticular disease, which appear as a pouch in the colon walls by making a larger soften stool which requires less pressure to pass through the digestive system (Bassotti et al., 2003).
- In the small intestine, soluble fibre binds to the cholesterol molecules and prevent their absorption(Brown et al., 1999).
- Soluble fibres limits the absorption and digestion of carbohydrates and decreases insulin demand in the body thereby stabilizing glucose levels (de Leeuw et al., 2004).
- Soluble fibre makes the contents of the stomach viscous increases the gastric emptying time.
- An increase intake of dietary fibre may be useful for the treatment of obesity as well as diabetes mellitus (Mehta, 2005, 2009). Fibre rich foods are generally satisfying without being calorically dense (Smith, 1987).
- A diet rich in carbohydrate and fibre, based particularly on legumes, vegetables, fruits and whole cereals, may be beneficial for treating diabetic patients because of its multiple effects on various cardiovascular risk factors (de Mello et al., 2009).
- Adequate consumption of food rich in dietary fibre has been linked with decreased risk of developing diet related chronic diseases (WHO, 2003).
The role of dietary fibre and its digestibility is becoming increasingly important in the context of health transitions as the population shifts to processed, refined, and convenient foods. An increase in the intake of dietary fibre is also associated with increased satiety and weight loss. It is essential for older people to maintain an adequate intake of dietary fibre, particularly the bulk forming cereal fibre. Intake of a nutritious diet including whole grains breads and cereals, legumes, oats, barley, fruits & vegetables and nuts & seeds can provided adequate amount of favourable fibre. Nuts and seeds and legumes—like black beans, chickpeas, and lentils—can be great high-fibre additions to salads, meals, or snacks. Smoothies can be a convenient way to get some extra fibre in your diet. When you are beginning to add more fibre to your diet it is important to introduce those foods slowly. Adding too much fibre too quickly can lead to intestinal gas, abdominal bloating and cramping. Increasing your fibre intake gradually over a few weeks allows your digestive system time to adjust to the change. It is also important to stay hydrated with plenty of water. Fibre works best when it absorbs water.
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