When people typically think of macronutrients the big three spring to mind; Carbohydrate, Fat and Protein. Whilst they are vital to achieving optimal nutrition, Dietary Fibre is often forgotten and overlooked.
So what is Fibre?
Dietary fibre is a polysaccharide that escapes digestion in the gastrointestinal tract, in simple terms it is the indigestible part of carbohydrate. Rich sources of fibre are fruit and vegetables, as well as wholegrains.
Fibre can be generally classified into two categories;
Soluble Fibre– As the name suggests this fibre dissolves in water. Inside the body the fibre dissolves to form a gel. It is helpful in normalising both blood glucose and levels of harmful LDL cholesterol and Triglycerides. Soluble fibre is found in oats, fruits and vegetables as well as beans and pulses.
Insoluble Fibre– This form of fibre does not dissolve in water and its main function is to decrease transit time in the GI tract and increase the bulk of stools preventing constipation. Wholegrains as well as fruit and vegetables are good sources of insoluble fibre.
We need both types of fibre, but the good news is if we eat a varied diet based around fruit and vegetable consumption, as well as including wholegrains we will be providing our body with plenty of fibre.
The NHS recommends that adults aim to consume a minimum of 30 grams on a daily basis. This would be a good target to aim for most.
Dietary fibre is essential for a health digestive system, and research has linked it to a reduced risk of a wide range of lifestyle diseases, including cardiovascular disease, type 2 diabetes as well as a number of different cancers.
How does this work?
Many reasons are hypothesised by experts as to how diets high in dietary fibre exert their protective effects against disease.
Reduced Overall Energy Intake- Let us start with the basics, foods that are high in dietary fibre tend to be minimally processed and nutrient dense, as well as achieving satiety. Large amounts of these foods can be eaten without providing excess energy. Compare this to energy dense foods that are often nutrient poor and heavily processed. It could be quite simply that people who eat diets high in fibre tend to have much better quality diets and are less likely to be overweight. We know that being overweight or obese increases our risk of disease.
Reduced Energy Availability- This is linked to the point above, carbohydrate foods that are higher in dietary fibre have less energy overall that is available to be utilised by the body. If a food contains 9 grams of carbohydrate, with 4kcal per gram the available energy from carbohydrate would be 36kcal. However if 3 grams of this carbohydrate is from dietary fibre this means that only 24 kcal of carbohydrate energy is available, as the 3 grams of fibre cannot be utilised as a source of energy. This will lead to a reduced total energy intake over the course of the day.
Sustained Energy Release- Fibre can delay the release of glucose into the blood as well as producing a smaller insulin response following food ingestion. This will result in a more sustained release of energy, this will have an effect on overall energy levels and is likely to dictate activity patterns and subsequent food intake for the rest of the day. These choices will go a long way towards influencing behaviours which may help to reduce the risk of disease. The smaller insulin response may also help to reduce the risk of developing type 2 diabetes.
Lower Cholesterol Levels– One of the specific effects of soluble fibre is its role in helping to control levels of bad LDL cholesterol and Triglycerides in the blood. Higher levels of these fats in the bloodstream have been linked to an increased risk of cardiovascular disease.
Shorter Transit time and reduced exposure to Carcinogens- As discussed fibre can help to reduce the amount of time that the stool spends in the digestive tract, and with that reducing the exposure to potential harmful, cancer causing carcinogens.
What Can I do?
- Swap white refined carbohydrates such as bread, pasta, rice and bread for the wholegrain varieties.
- Aim for at least 8-10 portions of fruit and vegetables each day. Base your meals around these rather than starchy carbohydrates.
References
Dietary Fibre Intake and risk of Cardiovascular Disease: Systematic Review and Meta-Analysis. Greenwood, D.C et al. BMJ 2013; 347:6879.
Wholegrain Consumption and risk of Cardiovascular Disease, Cancer, and all causes of Specific Mortality: Systematic Review and dose-response meta-analysis of prospective studies. Aune, D et al. BMY 2016; 353:2716.