How much fibre should I eat every day?
Most of us don’t eat enough dietary fibre but, with growing evidence of its many benefits, how much should we be eating? Nutritionist Kerry Torrens explains
What is fibre and why is it important?
Fibre is the blanket term given to the non-digestible, mainly carbohydrate material, found in plants. The term refers to the part of the plant which our digestive enzymes can’t break down, so it passes through our digestive system relatively unchanged. Examples include lignins in flaxseeds, beta-glucans in oats and polysaccharides, including cellulose in root vegetables.
Adequate intakes of dietary fibre are associated with a lower risk of heart disease, stroke, type 2 diabetes and colon cancer. Choosing fibre-rich foods also makes us feel fuller, improves our digestion and helps prevent constipation. When consumed regularly, fibre supports gut health and may over time increase the diversity of the bacteria that live in our gut, it also helps us maintain a healthy weight, supports our cholesterol balance and regulates hormones.
What are the different types of fibre?
Until recently, fibre was categorised as soluble or insoluble, but research now reveals there are many more types of fibre and each has different properties depending on its origin and how it's been processed. These properties include how well it dissolves (solubility), how thick or gel-like it becomes (viscosity) and whether the fibre can be fermented by our gut bacteria.
Examples of different fibres and their properties include:
- Pectin in fruit, such as apples and pears, and beta-glucans in oats and barley – these are largely soluble fibres because they dissolve and become gel-like when mixed with liquids.
- Cellulose found in wholewheat flour, beans and pulses is insoluble and passes through our digestive system, relatively unchanged.
- Resistant starch found in cooked and cooled potatoes and pasta as well as underripe bananas – this type of fibre is both soluble and fermentable.
- Fermentable fibre, also referred to as ‘prebiotic’ because it provides a source of fuel for our gut bacteria – an example is the inulin found in onions, garlic and asparagus.
What are the benefits of the various types of fibre?
Viscous fibres, that are mostly soluble, thicken when mixed with fluid – these include gums, pectin, beta-glucans and the fibre found in psyllium. These fibres form a gel-like substance in the gut which slows our digestion and the speed we absorb nutrients, they may also affect the absorption of prescription medication, so refer to your GP if this is relevant to you. We make use of these physical properties in cooking, for example, when we make preserves such as jam, the fibre pectin is key to getting a good set.
Insoluble fibres aren’t changed by our digestion and they pass into the large intestine where they act as a bulking agent, helping to prevent constipation. Eating high levels of these types of fibre throughout our lifetime may help lower our risk of developing conditions like haemorrhoids as well diverticulitis. Similarly, resistant starch, as its name suggests is resistant to digestion, but is fermentable and broken down by our gut bacteria in the large intestine. Studies suggest that when we include foods rich in resistant starches we benefit from better blood sugar levels, improved appetite management and more efficient digestion.
Fermentable fibre, just like carbs, fats and protein, provides a source of energy (calories), on average 2 kcal per gram. Once in the colon these fermentable fibres are broken down by gut bacteria, fuelling them and creating by-products called short chain fatty acids (SCFA). These SCFAs feed the cells of our colon, help make our immune system more robust, improve our tolerance to certain foods and regulate our allergy response.
What are the signs that I’m not eating enough fibre?
Several telltale signs may suggest you’re not getting enough fibre, these include:
- You get hungry soon after eating
- You experience blood sugar swings and may feel tired and sluggish after a meal
- Your cholesterol levels are higher than recommended
- You’re overweight
- You experience hormonal fluctuations
- You’re frequently constipated and may suffer from haemorrhoids
How much fibre should I be eating each day?
As part of a balanced, healthy diet the UK government recommends that an average adult should increase their fibre intake to 30g per day. Most of us fall short of this amount – good sources include fresh and dried fruit, vegetables, beans and pulses, nuts, seeds and wholegrain cereals.
Children, depending on their age, should be eating between 15-25g of fibre per day.
What are the downsides of too much fibre?
If you increase your fibre intake too quickly you may experience symptoms like abdominal bloating, cramping and wind. However, as you adjust to a higher fibre intake your digestive system and gut bacteria should adapt and the symptoms subside.
When you start to increase the fibre in your diet, be sure to drink extra fluids to help the fibre do its job properly, and plan to make these dietary changes over a period of weeks rather than days to allow your digestion time to adapt.
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Is extra fibre safe for everyone?
You should be careful adding significantly more fibre to your diet, especially if you are on prescribed medication, because fibre in the form of pectin (fruit) and beta-glucans (oats) may affect the body's ability to absorb certain medications, including aspirin. Likewise, if you are on medication or insulin to control diabetes, you should be aware that fibre may reduce your blood sugar levels and necessitate an adjustment to your medication.
Those recently diagnosed with diverticulitis, should follow a low-fibre diet until their condition is suitably managed. Similarly, if you have irritable bowel syndrome you may find your tolerance of fermentable fibre is low and you should minimise these fibres in your diet, at least until your condition is under control. These include inulin found in asparagus, onions and artichokes, and oligo-fructose found in bread, cereals, ripe bananas and some vegetables. Speak to your GP or a registered dietician for further advice – they may suggest you follow a low FODMAP diet under their professional supervision.
If you are looking to increase your fibre intake refer to your GP or a registered dietician – this is especially relevant if you are taking prescription medication or have been diagnosed with a gut condition, such as diverticulitis or IBS.
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