People who eat higher amounts of fibre and whole grains have lower rates of chronic diseases compared with people who eat lesser amounts. Observational studies and clinical trials conducted over nearly 40 years reveal the health benefits of eating at least 25 to 29 grams of dietary fibre each day, according to a series of systematic reviews published in The Lancet.
The results suggest a 15 to 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.
Eating fibre-rich foods also reduced the risk of developing coronary heart disease, stroke, type 2 diabetes and colorectal cancer by 16 to 24%. Per 1,000 participants, the impact translates into 13 fewer deaths and six fewer cases of coronary heart disease.
In addition, a meta-analysis of clinical trials suggested that increasing fibre intakes was associated with lower body weight and blood cholesterol, compared with lower intakes.
(A meta-analysis pools data from multiple prior studies using special statistical methods to report the findings as if it were one large study. Meta-analysis is often used to assess the clinical effectiveness of a nutritional treatment or drug.)
The study was commissioned by the World Health Organization to inform the development of new recommendations for optimal daily fibre intake and to determine which types of carbohydrate provide the best protection against chronic diseases and weight gain.
Most people worldwide consume less than 20 g of dietary fibre per day. In the US, fibre intake among adults averages 15 g a day. Rich sources of dietary fibre include whole grains, pulses, vegetables and fruit.
About the research review
The researchers 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: breast, endometrial, esophageal and prostate cancer.
The authors only included studies with healthy participants, so the findings cannot be applied to people with existing chronic diseases.
Fibre and health
For every 8 gram increase of dietary fibre eaten per day (the amount found in about one-third cup of 100% bran cereal or one cup of raspberries) , total deaths and incidence of coronary heart disease, type 2 diabetes and colorectal cancer decreased by 5 to 27%. Protection against stroke, and breast cancer also increased.
Consuming 25 to 29 grams each day was beneficial, but the data suggest that higher intakes of dietary fibre could provide even greater protection.
Whole grains and health
For every 15 gram increase of whole grains eaten per day, total deaths and incidence of coronary heart disease, type 2 diabetes and colorectal cancer decreased by 2 to 19%. Higher intakes of whole grains were associated with a 13 to 33% reduction in chronic disease risk -- translating into 26 fewer deaths per 1,000 people from all-cause mortality and seven fewer cases of coronary heart disease per 1,000 people.
The meta-analysis of clinical trials involving whole grains also showed a reduction in body weight. Whole grains are high in dietary fibre, which could explain their beneficial effects.
Link between glycemic index and health less clear
The study also found that diets with a low glycemic index and low glycemic load provided limited support for protection against type 2 diabetes and stroke only. Foods with a low glycemic index or low glycemic load may also contain added sugars, saturated fats, and sodium.
How fibre guards against disease
Fibre-rich whole foods that require chewing and retain much of their structure in the gut increase satiety and help weight control and can favourably influence blood cholesterol and glucose levels. The breakdown of fibre in the large bowel by the resident bacteria has additional wide-ranging effects including protection from colorectal cancer.
Note, this study mainly relates to naturally-occurring fibre rich foods rather than synthetic and extracted fibre, such as powders, that can be added to foods.
Source: The Lancet Online First, January 10, 2019.
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