The ‘F’ Word…
Filling up on fibre may no longer be as fashionable as it used to be but we could all do with eating more of it.
So, where did it all start? Nearly 2,500 years ago, Hippocrates was the first to recognise the benefits of fibrous food by praising wholemeal bread ‘for its salutary effect upon the bowel’. So what exactly is fibre and why should we be making an effort to increase our intake of it?
What is Fibre?
Fibre is found in plant foods and can be divided into two types. Firstly, there is the type that helps to give structure to leaves and stalks, stems and fruits, which is known as insoluble fibre. It is not possible for our digestive systems to break down this type of fibre very effectively, so much of it passes through our intestines almost intact. While this type of fibre makes its journey through our small intestine and colon, it seems to have lots of benefits, not least helping to bulk out our stools, ease bowel movements and avoid constipation.
Insoluble fibre is what gives wholemeal bread and wholegrain pasta its brown colour, but it is also present in lots of colourful fruits and vegetables. For example, it is in the stalks of broccoli, where it helps to give structure and the white membranes you find in citrus fruit such as oranges and grapefruit.
The second type of fibre is known as soluble fibre and is found in fruits such as apples and pears, vegetables such as peas and lentils and also in nuts and cereals including oats. Soluble fibre is made up of gums, pectins (used to help set jam) and mucilages that swell up when they come into contact with water in your stomach and intestine, turning the soluble fibre into a sticky glue-like substance. When this happens it helps to keep us feeling full as well as having a beneficial effect on cholesterol and blood-sugar levels.
How much fibre do we need?
Different countries have varying guidelines for the total amount of fibre we should be aiming for. In the UK this is 18g a day; in the US this is 25-35g a day. To give this a sense of perspective, it is still not very much compared with regular daily intakes in, for example, rural African countries, where it is possible to get 60g a day through eating the local, largely unrefined diet that is full of both types of fibre.
Studies looking at the consequences of different diets have shown that, in the UK, we produce around 100g of stools a day and it takes 83 hours for a meal to complete its journey through our digestive systems. However, our African counterparts, who eat much higher fibre diets, produce almost five times this and it takes just 34 hours to pass through their digestive systems.
Rather than worrying about the exact amount of fibre we should be eating, the general message is that a lot of us are not hitting the UK target. Most adults would benefit from eating more fibre, so consider swapping to wholegrain pastas, bread, rice and cereals and tucking into plenty of fruit and vegetables each day.
How does soluble fibre help to lower cholesterol and blood-sugar levels?
The soluble fibre found in fruits such as apples and pears, plums and apricots; vegetables such as baked beans, peas and red kidney beans and porridge oats, literally grabs hold of cholesterol in your intestines and carries it out of your body. This means that less cholesterol is absorbed back into your blood from your gut and therefore cholesterol levels in your blood will then fall. As for sugar, because soluble fibre forms a gel-like substance in your gut, it physically slows down the speed of sugar absorption through your intestine wall. This, in turn, appears to reduce the need for the hormone insulin, which could benefit people with diabetes as well as help to reduce sugar highs and lows for everybody. Steady blood-sugar levels appear to lower our cravings for more sugar and keep us feeling full.
Will eating a high-fibre diet help you lose weight?
It has been found that while lean adults in England have been found to eat an average of 19g of fibre a day, those who are obese chomped through just 13g of fibre even through they were eating more calories. So, the indication is that high-fibre diets may help you to control your weight.
It appears, for instance, that fibre has a modest effect on helping you to stay full not just because of the effect of the soluble fibre, but also because fibre-rich foods take a lot of chewing. Time yourself eating a bowl of muesli one morning and the next day try it with a bowl of refined cereal such as Frosties. While the former can take a good 8-10 minutes, the latter takes more like five minutes. The action of chewing increases feelings of fullness – it sends messages to the ‘I’m full’ parts of your brain. Secondly, because foods high in soluble fibre take longer to pass through your digestive system, various other ‘I’m full’ parts of the brain are stimulated for longer too. Fibre also bulks out food, so you enjoy a greater physical satisfaction when you eat fibre-rich foods – another important role fibre can play in weight loss. For example, an apple can fill your whole hand, weigh around 100g and yet gives you just 100 calories. Alternatively, you could eat about a third of a Mars bar – no bigger than a small box of matches – and consume the same number of calories. Given that we ‘eat with our eyes’ it is not surprising that fullness is also related to when the food portions look like. High-fibre foods are bulky in nature, look larger and make you instantly feel as though you have eaten more. Fibre may also slightly reduce the number of calories we absorb from foods.
Put all of these facts together and you can see how a high-fibre diet could well aid your goal of shedding pounds.
Do you want to eat more fibre but it makes you feel bloated and gassy? How to overcome this:
Some types of carbohydrate found in beans and lentils are not digested in your small intestine. When these make it through to your large intestine, special fibre-eating bacteria feed on them, producing the gases that make you feel bloated and give you wind. If you find this is a problem then try to introduce extra servings of fibre-rich pulses to your diet gradually so that your bacteria adapt. For many people this helps to increase their tolerance and the problem passes.
For those who have irritable bowel syndrome or disorders of the colon such as diverticulitis or Crohn’s disease, it is vital to discuss your diet with your doctor and a registered dietician so that you can get your fibre intake balanced and fine-tuned to suit your individual system.
Are there any downsides to eating fibre-rich foods?
Some types of fibre interfere with your body’s ability to absorb important minerals such as iron and zinc. It is thought that your body adapts to a raised intake of fibre over time by increasing the percentage of these minerals absorbed in the intestine. But, if you are making a conscious effort to eat more fibre, then taking a multivitamin and mineral supplement at the same time will overcome this potential problem.
What is beta-glucan?
Beta-glucan is the soluble fibre in oats that acts like a sponge during digestion, soaking up and helping to remove some of the excess cholesterol in your digestive system. Eating oats as part of an overall healthy diet appears to help to reduce the risk of heart disease as well as filling you up and keeping your energy levels steady for longer.