By Associate Professor Eleanor Beck, Expert on Fibre, Advanced APD, PhD, University of Wollongong
The sixth International Dietary Fibre Conference was held in Paris from June 1-3, 2015. As a parent, how could I want anything more than a few days escape from my children in Paris? Interestingly though, the key message of the conference is that fibre is just like children. Fibre, like a child, is not one thing, but many things; all fibres (and all kids) are different; they behave differently and affect us in many different ways. While we might not always want to choose to have fibre or fibre rich foods (like we choose sometimes to seek a little rest from our children), the evidence consistently shows that fibre is important for health and increasingly the research, as discussed at the conference, is showing that variety in the fibres we eat is essential, because as Kaisa Poutanen of VTT Technical Research Centre, Finland quoted at the conference – “fibre is not fibre but rather fibre is a many splendored thing”.
The conference featured a variety of scientists presenting engaging summaries of the latest meta-analyses on the link between fibre intake and health. Data from large cohorts, with over 1 million participants (in some cases) were investigated and identify that for every 10g of total fibre intake, there is approximately a 10% reduction in all-cause mortality (you are just less likely to die!).(1) Interestingly, when researchers looked at the source of the fibres, it appears that fibre from grain foods , and to a lesser extent vegetable fibre is associated with significantly lower mortality and that no significant association was found with fibre from fruit.(2) Research also suggests that higher fibre intakes decreases risk of obesity, coronary heart disease, hypertension, diabetes and certain types of cancers, however identifying the mechanisms by which fibre protects against these diseases is difficult because any one food may have many different fibres within the food, we eat a variety of foods and we often process or cook our food in a variety of ways.
For researchers, like myself, to explore the complex ways in which fibres promote health, it is important to consider the chemical structure of the fibre, including the structure and length of the carbohydrate polymers (essentially fibres are long chains of carbohydrate molecules), the cell wall structure and what other compounds are associated with the fibre within the food and how they interact. Given all of these things impact the functionality of the fibre, it is not surprising that fibre has been attributed to such a wide varied range of positive health outcomes such as improved laxation (keeps you regular), decreased cholesterol levels, improved blood glucose responses and satiating effects (increased feeling of fullness). These health benefits are likely related to the mechanisms by which fibres alter the rate of digestion and the way our food moves through our digestive system. However as was discussed at the recent conference there are a number of other effects such as anti-inflammatory actions and immunomodulatory effects which are also likely to account for the health benefits of fibres and these effects are now increasingly under investigation. In particular, we know that fibres alter the human gut microbiome (the community of bacteria living in our digestive systems) and often stimulate the growth of beneficial bacteria. The presence of fibre in the large bowel also feeds our gut microbiota in varied ways such that the bacteria will also produce different metabolites, starting a cascade of reactions as varied as modifying gut permeability to increasing release of satiating hormones. This emerging area of research reminds us that we need to understand the complexity of dietary fibre structures and how these variations impact on the physiology and evolution of microbes (bacteria) living in our gut. The amount of varied bacteria in our gut outnumbers the genetic variation in the human genome almost 10 fold and so the scientists investigating their impact on health certainly have their work cut out for them, but this will be essential to advance our understanding of how fibres affect health via changes to the gut microbiome.
So, as a researcher and as a parent I have some varied jobs to do. I know that to be diligent I need to not just look at how fibre affects individuals (in clinical trials) but I need to ensure the fibre (and the food overall) is well characterised to identify possible mechanisms of action. One of the reasons it is hard to identify individual fibre effects is that we have not been good at reporting all the details. It’s like having a toddler where you cannot possibly identify every hazard without serious investigation because they can find a mechanism to create havoc anywhere. As a parent, I need to ensure that my family and I eat fibre from all different sources to ensure that I can maximise the myriad of health effects possible with a healthy diet, but as a researcher, I need to remember that fibre is not just fibre, but rather a variety of complex molecules each with a variety of mechanisms which may influence health.
While there is still so much to learn, there is one positive outcome that everyone can agree on, and that is there are not negative studies on fibre. As our dietary guidelines advise: “enjoy a wide variety of nutritious foods …..every day: plenty of vegetables of different types and colours, and legumes/beans; fruit; grain (cereal) foods, mostly wholegrain and/or high cereal fibre varieties…”. The fifth fibre conference was in Rome, this one in Paris and the next scheduled for the Netherlands in 2018. Who knows what could happen there, away from my kids!
- Liu L, Wang S, Liu J. Fiber consumption and all-cause, cardiovascular, and cancer mortalities: A systematic review and meta-analysis of cohort studies. Molecular Nutrition & Food Research. 2015;59(1):139-46.
- Kim Y, Je Y. Dietary Fiber Intake and Total Mortality: A Meta-Analysis of Prospective Cohort Studies. American Journal of Epidemiology. 2014;180(6):565-73.