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You may have heard quite a lot about fibre recently. Once considered a less glamourous part of our diet, it is now taking centre stage as we become more aware of its importance. I have been asked whether the way you cook food influences the fibre content, so I thought it would be helpful to outline a few pointers.

What is fibre?

Fibre is carbohydrate that resists digestion by enzymes in the small intestine and travels on to the large intestine where it is digested by bacteria. It is only found in plant foods. Once divided into two categories, ‘insoluble’ and ‘soluble’ fibre, we now know there are many different types of fibre with different health benefits.

Why is fibre good for you?

High fibre foods can help us feel full for longer, which can be useful if you are watching your weight. It is also key for ensuring a healthy gut and preventing constipation. Eating enough fibre has been associated with lowered risk of heart disease, stroke, type 2 diabetes and bowel cancer, and gut health is now being linked to mental well-being1,2 as well as eczema and immunity.1 We are learning more and more about the benefits of a particular type of fibre called prebiotics (sources include artichoke, asparagus, bananas, beans, lentils, garlic, leeks, onions, oats, barley, wheat). Prebiotics provide food for healthy bacteria to feed on in the gut, which improves the diversity of bacteria and this diversity seems to have a big impact on our health.1,2, 3, 4 Eating a variety of plant foods is recommended, as fibre from different sources have been shown to have varying health benefits. For example, the fibre in oats and fruit has been shown to reduce blood cholesterol, while the fibre in wholegrains has a greater impact on risk of bowel cancer.2

Food preparation

But how does the way we cook and prepare food affect the fibre content? Think of what was traditionally known as ‘insoluble fibre’ as the non-digestive fibrous parts of the plant including the skin. If you peel a fruit or vegetable you are removing the outer layer that contains lots of fibre, thus reducing its fibre content. For many fruits the outer layer is inedible, such as bananas, pineapple, melon, avocado etc. however for fruits and vegetables such as apples, pears, potatoes, carrots we would benefit from leaving the skin on. How you cook the fruit or vegetable, whether you decide to fry, boil, steam or roast will have little effect the fibre content, but how you choose to prepare it will. For example, mashed potato made with peeled potatoes, will contain less fibre compared to jacket potato (including skin).

Juice vs. smoothies

In making fruit juice we extract the liquid and discard the fibrous parts of the plant. Therefore, there is hardly any fibre in fruit juice. In making smoothies we blend the fruit or vegetable to make a pulp, keeping not only the juice but also the fibrous parts of the plant. Smoothies therefore contain more fibre than juices. However, although the fibrous parts of the fruits and vegetables are still there, they have been blitzed and cut up to be really small. We know that particle size has an impact on the benefit we get from fibre.2 The greater the particle size, the longer it takes for the food to be digested in the stomach, the fuller you feel for longer and the greater the benefit. A smoothie will be quicker for the body to digest compared to if you ate the whole fruit. So, although the fibre is still in the smoothie, the benefit you get from eating the fruit or vegetable has been reduced.

Choosing your grains

The ‘skin on’ principle can also be applied to grains. By eating whole grains that still have their outer fibrous bran layer on, you get more fibre. For example, white flour is ground wheat grain where the outer bran and the nutritious germ of the wheat has been removed, and wholemeal flour is ground whole wheat grain where the outer bran and wheat germ have been left intact. By eating white pasta/bread you are not getting the beneficial fibre that is found in wholemeal pastas and wholemeal/wholegrain breads.  The same principle applies to rice. The outer bran layer has been left on brown/wholegrain rice, so this is a higher fibre choice compared to white rice.

Choosing wholegrain and seeded breads over wholemeal bread is an even higher fibre choice as the bread is made not only from wholemeal flour, but has some wholegrains/seeds added in too, and as these have a bigger particle size than the flour, they provide additional benefit. Any bread/cereal product with added bran or wheat germ will contain added fibre.

Particle size is also relevant for oats. Oats are a great choice for increasing your fibre intake, however you can get an even greater benefit if you choose chunky varieties, as these take longer to digest in the stomach and may help you feel fuller for longer than refined oats.

Tips for getting the most fibre from your foods

Adults are recommended to consume 30g of fibre a day. This may sound like a lot, but if you make some simple swaps to every day foods you can easily increase your intake. The great news is that high fibre foods are also packed with vitamins and minerals and many (including pulses, nuts and seeds) are also a great source of protein. (Children need less fibre than adults and remember that babies have tiny tummies so be careful not to fill them up on too many high fibre foods.) Here are my top tips for increasing your fibre intake:

  • Start by increasing the fibre in your diet slowly and take note of any foods that may cause adverse effects such as bloating etc.
  • Drink lots of water as fibre absorbs water in the body.
  • Include a wide variety of plant foods in your diet to obtain all the different types of fibre.
  • Consume at least five portions of fruit and vegetables a day and leave the skin on where you can.
  • Choose wholemeal and wholegrain varieties of bread, pasta, rice and breakfast cereals.
  • Choose chunky varieties of oats and other grains and make your own muesli or porridge.
  • Swap and/or supplement meat dishes with pulses, for example add lentils to any bolognaise, soup or stew for texture and extra fibre.
  • Reliance on convenience foods lacking in fibre can make it difficult to reach recommendations, so try cooking from scratch as much as you can.
  • Instead of buying cakes and biscuits make your own fruit-based treats using wholemeal flours, you can even include vegetables!
  • Choose crisps with skins on and potato wedges instead of fries.
  • Some manufacturers now add fibre into convenience foods in the form of inulin, extracted from chicory root or sugar beet, which can contribute to fibre intake, so look out for it in the ingredients list of processed foods.

Hopefully that answers some of your fibre questions. For more information on recommended intakes for different age groups as well as examples of what 30g a day might look like visit the NHS. There is so much research on going in this area. Not only in the area of benefits of fibre, but also in relation to some of the side effects for example in irritable bowel syndrome (IBS) sufferers. If you do find you have adverse effects to fibre rich foods it might be worth speaking to a qualified dietitian.

References

  1. British Nutrition Foundation (BNF) Free webinar: Why is everybody talking about gut microbiota? Accessed on 2nd July 2018 Available here: https://www.nutrition.org.uk/nutritionscience/webinars/why-is-everybody-talking-about-gut-microbiota.html
  2. Nutrilicious Free Nutriwebinar: Dietary fibre: an old concept in new light? With Dr Megan Rossi, RD. Accessed 7th November 2018 Available here: http://nutrilicious.co.uk/fibre-nutriwebinar/
  3. Nutrilicious Free Nutriwebinar: The Gut Microbiome Feeding The Gut For Optimum Health. Accessed 6th December 2018 Available here http://nutrilicious.co.uk/the-gut-microbiome-webinar/
  4. British Nutrition Foundation (BNF) Free lunchtime webinar: The prebiotic potential of our diets – fibre and more. Accessed 12th December 2018. Available here: https://www.nutrition.org.uk/nutritionscience/webinars/bnf-webinar-the-prebiotic-potential-of-our-diets-fibre-and-more.html

rachel

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