Recommendations for fibre and wholegrain consumption in cardiovascular health and lipid management and the evidence behind them
Carbohydrate and fibre recommendations in lipid management (2019 ESC/ EAS Guidelines[1])
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[1] François Mach, Colin Baigent, Alberico L Catapano, et al, ESC Scientific Document Group, 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk: The Task Force for the management of dyslipidaemias of the European Society of Cardiology (ESC) and European Atherosclerosis Society (EAS), European Heart Journal, , ehz455, https://doi.org/10.1093/eurheartj/ehz455
Higher fibre and wholegrain intakes have been associated with a reduced risk of cardiovascular events and mortality [1],[2],[3],[4],[5]
Results from a recent series of systematic reviews and meta-analyses, including 185 prospective studies and 58 clinical trials, found a 15-30% reduced incidence of cardiovascular related mortality and Coronary Heart Disease (CHD) when comparing the highest dietary fibre intakes with the lowest intakes.[4] Risk reduction was greatest when dietary fibre intakes (from all sources including cereals, legumes, fruit and vegetables) was between 25g and 29g a day, although it was suggested that amounts greater than 30 g per day could provide additional benefits.
These observations are supported by evidence from clinical trials examining risk factors. Compared to lower intakes, higher intakes of fibre is associated with significantly lower body weight, systolic blood pressure, total cholesterol and LDL cholesterol.
Similar observations were seen with whole grain intake, suggesting the beneficial effects of whole grains could be in part due to their high dietary fibre content. One study found that 90g, or three servings of whole grains daily, was associated with a 19% reduced incidence of CHD[1].
The consistency between the trial and prospective study results, together with a dose-response relationship, provide support that the effect on cardiovascular disease (CVD) is likely to be causal and not as a consequence of confounding variables.
This finding is broadly in line with the 2015 recommendations made by the Scientific Advisory Committee on Nutrition to increase dietary fibre intake to 30 g per day [2].
When examining the impact of nutrients/ foods on CVD risk, it’s important to consider what these are replacing in the diet. For example, replacing 5% of energy intake from saturated fats with the equivalent energy from wholegrain carbohydrates is associated with a 9% lower risk from CHD. In contrast, replacing saturated fats with carbohydrates from refined starches/ added sugars is not significantly associated with CHD risk (1% higher incidence)[6]. It’s worthwhile noting that while the magnitude of effect of replacing saturated fat with whole grains is smaller in comparison to the effect of replacing saturated fat with unsaturated fat, the inclusion of whole grains remains an important feature of a heart healthy diet.
[1] Aune D et al. (2016) Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies BMJ;353:10 doi: https://doi.org/10.1136/bmj.i2716 https://www.bmj.com/content/353/bmj.I2716.full
[2] SACN. 2015 https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/445503/SACN_Carbohydrates_and_Health.pdf
[3] Threapleton D et al. (2013) Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis BMJ.;347:10 doi: https://doi.org/10.1136/bmj.f6879
[4] Reynolds R et al.(2019) Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet;393(10170):434-45
[5] Ha V et al. (2014) Effect of dietary pulse intake on established therapeutic lipid targets for cardiovascular risk reduction: a systematic review and meta-analysis of randomized controlled trials CMAJ. 186(8):E252-62
[6] Frank M. Sacks, et al (2017) Dietary Fats and Cardiovascular Disease A Presidential Advisory From the American Heart Association. Circulation;136:e1–e23. DOI: 10.1161/CIR.0000000000000510
Fibre and lipids
A Cochrane Systematic Review examining dietary fibre for the primary prevention of CVD found a significant beneficial effect of increased fibre on total cholesterol levels (‐0.20 mmol/L) and LDL cholesterol levels (‐0.14 mmol/L), but there was no effect on triglyceride levels. There was also a very small but statistically significant decrease in HDL levels (‐0.03 mmol/L) with increased fibre intake[1].
These findings were similar to an earlier systematic review and meta-analysis of randomised controlled studies which assessed the effect of whole grain compared with non-wholegrain foods on changes in total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. Results from 24 studies found wholegrain diets lowered LDL cholesterol (-0.09 mmol/L) and total cholesterol (-0.12 mmol/L), but not HDL cholesterol or triglycerides, compared with consumption of non-wholegrain control diets. Wholegrain oat appeared to be the most effective whole grain for lowering cholesterol (-0.17 mmol/L)[2].
[1] Hartley L, May MD, Loveman E, Colquitt JL, Rees K. (2016) Dietary fibre for the primary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews, Issue 1. Art. No.: CD011472. DOI: 10.1002/14651858.CD011472.pub2. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD011472.pub2/full
[2] Hollænder PL, et al (2015) Whole-grain and blood lipid changes in apparently healthy adults: a systematic review and meta-analysis of randomized controlled studies. Am J Clin Nutr. 102(3):556-72. doi: 10.3945/ajcn.115.109165. Epub 2015 Aug 12.
Substituting saturated fat for carbohydrate on lipids
Saturated Fatty Acids are the dietary factor with the greatest impact on LDL cholesterol. Compared to the benefits of substituting saturated for unsaturated fats on LDL cholesterol, studies have generally found that carbohydrates have a neutral effect.
However excessive consumption can have a negative effect on plasma triglycerides and HDL cholesterol levels. The detrimental effects of a high-carbohydrate diet on triglycerides mainly occur when refined carbohydrate-rich foods are consumed, while they are much less prominent if the diet is based largely on fibre-rich, wholegrain foods. This applies particularly to people with Diabetes Mellitus or Metabolic Syndrome.
Types of fibre
One classification of fibre is based on solubility – soluble dietary fibre (SDF) and insoluble dietary fibre (IDF).
- SDF is present in whole grains (e.g. oats, barley, and wheat), peas and beans, some fruits and vegetables, seeds and nuts.
- IDF can be present in foods such as whole-wheat flour, wheat bran, brown rice, nuts, beans, fruits and vegetables.
Most foods contain a mixture of both in varying proportions.
Findings from clinical studies have found SDFs can reduce total cholesterol and LDL cholesterol levels by 5–10 %[1].
Oats and barley are rich in a particular type of SDF - beta-glucan - which has been recognised for its cholesterol lowering benefits by the European Food and Safety Authority. A European health claim for cholesterol lowering has been approved at intakes of 3g a day and products providing a minimum of 1g of beta-glucan per serving may carry the claim[2],[3].
Pulses are also a good source of SDF. A systematic review and meta-analysis of 26 randomised controlled trials assessing the effects of dietary peas and beans on lipid levels and CVD risk reduction found that consuming around 130 g of beans a day resulted in a modest reduction of LDL cholesterol levels (-0.17 mmol/L, corresponding to a 5 % reduction from baseline)[4].
[1]Surampudi, P., Enkhmaa, B., Anuurad, E. et al. Lipid Lowering with Soluble Dietary Fiber. Curr Atheroscler Rep 18, 75 (2016). https://doi-org.rsm.idm.oclc.org/10.1007/s11883-016-0624-z
[2] COMMISSION REGULATION (EU) No 1160/2011 …referring to the reduction of disease risk: Oat beta-glucan. OJ. 2011;L 296:28. https://www.efsa.europa.eu/en/efsajournal/pub/1885
[3] COMMISSION REGULATION (EU) No 1048/2012…reduction of disease risk. Barley beta-glucan. OJ. 2012;L 310:40 https://www.efsa.europa.eu/en/efsajournal/pub/2471
[4] Ha V, Sievenpiper, et al. Effect of dietary pulse intake on established therapeutic lipid targets for cardiovascular risk reduction: a systematic review and meta-analysis of randomized controlled trials. CMAJ. 2014;186(8):E252–62.
Mechanism of action
There are a number of proposed mechanisms for fibre’s hypocholesterolaemic effects:
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Current intakes vs recommendations
UK adults, aged 19-64 years, consume around 19g of fibre a day which corresponds to 63% of UK dietary recommendations (30g/ day). Only 9% of adults are meeting the recommendations.[1],[2]
There are no UK specific recommendations for wholegrains per se, although the eatwell plate advises: ‘Starchy foods should make up just over a third of the food we eat. Choose wholegrain or higher fibre versions of products like breads, rice or pasta.’
[1] PHE. 2018. hiips://www.gov.uk/government/statistics/ndns-results-from-years-7-and-8-combined
[2] PHE. 2016. hiips://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/ file /618167/government_dietary_recommendations.pdf
What about low carbohydrate diets?
While a low-carbohydrate diet (LCD) has become a popular strategy for weight loss and weight management in recent years, the long-term associations of carbohydrate-restricted diets with health outcomes remain controversial. Read our blog on low carbohydrate diets.
As described previously, the growing body of evidence suggests it’s the carbohydrate quality rather than quantity which determines major health outcomes, including CVD[1]. Restricting carbohydrates from the diet can result in lower intakes of fibre rich foods and whole grains. Depending on what replaces carbohydrate rich foods in the diet, a low carbohydrate diet may also result in higher intakes of saturated fat.
A particular concern is the growing popularity of very low carbohydrate, high fat diets such as the ketogenic diet. The US National Lipid Association Nutrition and Lifestyle Task Force recently published a scientific statement on the effect of these types of diets on body weight and cardiometabolic risk factors, including lipids[2]. The Task Force found that studies show mixed effects on LDL cholesterol levels, with some studies showing an increase. This appears to be related to the saturated fat content of the diet. They also expressed concern for ketogenic diets being used by people with hypercholesterolaemia, particularly Familial Hypercholesterolaemia, and concluded that this diet is contraindicated for these conditions. Read our blog on ketogenic diets and lipids.
[1] Reynolds R et al.(2019) Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet;393(10170):434-45
[2] Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force
Kirkpatrick, Carol F. et al. Journal of Clinical Lipidology, Volume 0, Issue 0. https://www.lipidjournal.com/article/S1933-2874(19)30267-3/fulltext
