- Non-communicable diseases (NCDs) such as cardiovascular disease, stroke, diabetes and cancer are on the rise
- Eating a high fiber diet can reduce the risk of non-communicable disease
- Adding fiber-rich foods such as whole grains, pulses, fruits, and vegetables to your diet can lower your body weight and bad cholesterol levels, thereby protecting against NCDs
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The results suggest a 15-30 percent decrease in all-cause and cardiovascular-related mortality when comparing people who eat the highest amount of fiber to those who eat the least. Eating fiber-rich foods also reduced the incidence of coronary heart disease, stroke, type 2 diabetes and colorectal cancer by 16-24 percent. 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 fiber intakes were associated with lower body weight and cholesterol, compared with lower intakes.
New Recommendations for Optimal Daily Fiber Intake
The study was commissioned by the World Health Organization to inform the development of new recommendations for optimal daily fiber intake and to determine which types of carbohydrate provide the best protection against non-communicable diseases (NCDs) and weight gain.
"Previous reviews and meta-analyses have usually examined a single indicator of carbohydrate quality and a limited number of diseases, so it has not been possible to establish which foods to recommend for protecting against a range of conditions," says corresponding author Professor Jim Mann, the University of Otago, New Zealand.
"Our findings provide convincing evidence for nutrition guidelines to focus on increasing dietary fiber and on replacing refined grains with whole grains. This reduces incidence risk and mortality from a broad range of important diseases."
A team of 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, oesophageal and prostate cancer. The authors only included studies with healthy participants, so the findings cannot be applied to people with existing chronic diseases.
- For every 8g increase of dietary fiber eaten per day, total deaths and incidences of coronary heart disease, type 2 diabetes, and colorectal cancer decreased by 5-27 percent. Protection against stroke and breast cancer also increased.
- Consuming 25g to 29g each day was adequate, but the data suggest that higher intakes of dietary fiber 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 percent.
- Higher intakes of whole grains were associated with a 13-33 percent reduction in NCD 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 showed a reduction in bodyweight. Whole grains are high in dietary fiber, 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. Foods with a low glycaemic index or low glycaemic load may also contain added sugars, saturated fats, and sodium. This may account for the links to health being less clear.
"The health benefits of fiber are supported by over 100 years of research into its chemistry, physical properties, physiology and effects on metabolism. Fiber-rich whole foods that require chewing and retain much of their structure in the gut increase satiety and help weight control and can favorably influence lipid and glucose levels. The breakdown of fiber in the large bowel by the resident bacteria has additional wide-ranging effects including protection from colorectal cancer." says Professor Jim Mann.
While their study did not show any risks associated with dietary fiber, the authors note that high intakes might have ill-effects for people with low iron or mineral levels, for whom high levels of whole grains can further reduce iron levels. They also note that the study mainly relates to naturally-occurring fiber-rich foods rather than synthetic and extracted fiber, such as powders, that can be added to foods.
Commenting on the implications and limitations of the study, Professor Gary Frost, Imperial College London, UK, says, "[The authors] report findings from both prospective cohort studies and randomized controlled trials in tandem. This method enables us to understand how altering the quality of carbohydrate intake in randomized controlled trials affects non-communicable disease risk factors and how these changes in diet quality align with disease incidence in prospective cohort studies. This alignment is seen beautifully for dietary fiber intake, in which observational studies reveal a reduction in all-cause and cardiovascular mortality, which is associated with a reduction in body weight, total cholesterol, LDL cholesterol, and systolic blood pressure reported in randomized controlled trials.
There are some important considerations that arise from this Article.
- First, total carbohydrate intake was not considered in the systematic review and meta-analysis.
- Second, although the absence of an association between the glycaemic index and load with non-communicable disease and risk factors is consistent with another recent systematic review, caution is needed when interpreting these data, as the number of studies is small and findings are heterogeneous.
- Third, the absence of quantifiable and objective biomarkers for assessing carbohydrate intake means dietary research relies on self-reported intake, which is prone to error and misreporting. Improving the accuracy of dietary assessment is a priority area for nutrition research.
Source-Eurekalert