Researchers reviewed and analysed results from observational studies and clinical trials conducted over almost 40 years to look at the health benefits of eating at least 25g to 29g or more of dietary fibre a day.
Globally, most people consume less than 20g of dietary fibre per day. In 2015, a report** by the UK Scientific Advisory Committee on Nutrition recommended an increase in dietary fibre intake to 30g per day, but only 9% of UK adults manage to reach this target.
Rich sources of dietary fibre include whole grains, pulses, vegetables and fruit.
The World Health Organization commissioned the study to inform the development of new recommendations for optimal daily fibre intake.
For their study, researchers from the University of Otago in New Zealand and the University of Dundee included 185 observational studies containing data that relate to 135 million person years and 58 clinical trials involving 4,635 adult participants.
They focused on premature deaths from and incidence of coronary heart disease, cardiovascular disease and stroke, as well as incidence of type 2 diabetes, colorectal cancer and cancers associated with obesity.
The results suggested there was a 15-30% decrease in all-cause and cardiovascular related mortality when comparing people who eat the highest amount of fibre to those who eat the least.
Analysis showed that for every 8g increase of dietary fibre eaten per day, total deaths and incidences of coronary heart disease, type 2 diabetes and colorectal cancer decreased by 5-27%.
Protection against stroke, and breast cancer also increased. Consuming 25g to 29g each day was adequate but the data suggested that higher intakes of dietary fibre could provide even greater protection.
For every 15g increase of whole grains eaten per day, total deaths and incidences of coronary heart disease, type 2 diabetes and colorectal cancer decreased by 2-19%.
Higher intakes of whole grains were associated with a 13-33% reduction in non-communicable disease risk.
Overall, if 1,000 people changed from a low fibre (less than 15g per day) to a high fibre (25-29g) diet, this would mean 13 fewer deaths and six fewer cases of coronary heart disease.
The meta-analysis of clinical trials involving whole grains also showed a reduction in bodyweight. Whole grains are high in dietary fibre, which could explain their beneficial effects.
The study also found that diets with a low glycaemic index and low glycaemic load provided limited support for protection against type 2 diabetes and stroke only.
While the study did not show any risks associated with dietary fibre, the authors noted that high intakes could have ill-effects for people with low iron or mineral levels, for whom high levels of whole grains can further reduce iron levels.
Corresponding author Professor Jim Mann FROM the University of Otago said: “Our findings provide convincing evidence for nutrition guidelines to focus on increasing dietary fibre and on replacing refined grains with whole grains. This reduces incidence risk and mortality from a broad range of important diseases.”
Fellow author John Cummings, emeritus professor of experimental gastroenterology at University of Dundee’s School of Medicine, said: “This is a defining moment in the fibre story.
“The work that we have done particularly on fibre and the gut micro flora, in Cambridge and in recent years in Dundee, means we have enough evidence from population studies, human experimental work and the biochemistry and physiological of fibre to be confident of the clear benefits to health. Fibre has come of age as a unique and essential nutrient.”