An Otago-led systematic review published in The Lancet finds people with a diet high in fibre and whole grains have lower rates of a range of chronic diet-related diseases.
Rates of heart disease – including death, colon cancer and type 2 diabetes were lower in people who eat at least 25g of fibre each day – and benefits increased with intake. The study, which looked at 40 years of data, aimed to inform new global recommendations on fibre intake. The benefits were less clear from eating foods with a low glycaemic index and glycaemic load.
The SMC asked experts to comment on the review. Feel free to use these comments in your reporting.
Dr Elaine Rush, Professor of Nutrition, Auckland University of Technology, comments:
“A substantial body of evidence from 185 prospective studies and 58 clinical trials show that high compared with low intakes of dietary fibre are associated with a 15-30 per cent decrease in all-cause and cardiovascular mortality and have beneficial effects on lowering body weight, systolic blood pressure and cholesterol.
“This research presents a substantial body of evidence that we should be eating more whole plants to delay dying and reduce disease. Dietary fibres are constituents of all plants. Animal products including meat and dairy DO NOT contain fibre. Whole grains, commonly consumed by and easily available to New Zealanders at a reasonable price and will store well include whole grain wheat, corn kernels (tinned), brown rice and oats. Uncooked, every 100g of these foods contains more than 10g of dietary fibre. We also need to eat more vegetables and fruit and legumes such as peas, beans and lentils.
“From New Zealand, we export enough edible plants to more than feed the population adequately three or more times over what they need. The argument, for eating more plants and a variety of wholesome foods, that really matters for our future children, is that it will also help reduce carbon emissions and improve water supplies – and keep our planet healthier and inhabitable.
“It is not easy to increase fibre in the diet. An example of how we could achieve 25 to 29 grams of fibre a day is to eat:
– half a cup of rolled oats (9g fibre),
– 2 weetbix (3g),
– 1 thick slice of wheatmeal bread (2g),
– 1 cup of cooked lentils (4g)
– a potato cooked with the skin on (2g),
– half a cup of silverbeet (1g),
– a carrot (3g),
– an apple with the skin on (4g).”
No conflicts of interest.
Dr Kathryn Bradbury, Nutritional Epidemiologist, University of Auckland, comments:
“This comprehensive article presents a series of systematic reviews on carbohydrate quality and chronic disease outcomes.
“The results show that there is good evidence from observational studies that higher intakes of dietary fibre are associated with a lower risk of disease, including bowel cancer and coronary heart disease. This is backed up by systematic reviews of trials, which show good evidence that higher intakes of fibre are associated with lower body weight, blood pressure and blood cholesterol.
“Likewise, there is good evidence that higher intakes of wholegrains are associated with a lower risk of bowel cancer, and lower body weight.
“These findings are particularly relevant for New Zealand, because we have one of the highest rates of bowel cancer in the world. Also, with the rise in popularity of so-called ‘Paleo’ and low carbohydrate diets, this study reminds us that dietary fibre (from fruit, vegetables and wholegrains) reduces the risk of chronic disease.”
Conflict of interest statement: Professor Jim Mann was one of my PhD supervisors. I have no other conflicts of interest to declare.
Our colleagues at the UK SMC also gathered the following comments, feel free to use them in your reporting.
Prof. Nita Forouhi, MRC Epidemiology Unit, University of Cambridge, comments:
“We need to take serious note of this study, based on a robust analysis and complementary findings from both observational and randomised trial evidence. This study effectively re-endorses that the UK Government advice to consume 30g fibre per day is pretty spot on. The onus is on individuals themselves, as well as public agencies, to make it happen, as average fibre intakes remain woefully low at a population level in the UK.
“This research did not study total carbohydrate intakes specifically, but its findings do imply that, though increasingly popular in the community at large, any dietary regimes that recommend very low-carbohydrate diets should consider the opportunity cost of missing out on fibre from whole grains. This research confirms that fibre and whole grain intakes are clearly important for longer term health.
“Ultimately this research provides a solid foundation that when it comes to carbohydrates, the quality matters very much, over and above the debate on quantity. Whole grain foods are typically high in fibre, and this research provides further evidence to highlight their importance and support a shift in our diets from processed and refined foods in the food supply chain towards more fibre-rich whole grain foods.”
Conflict of interest statement: “I am a member of the Joint SACN/NHS-England/Diabetes-UK Working Group on ‘lower carbohydrate diets compared to current government advice for adults with type 2 diabetes’. Views expressed are my own, not the Group’s.”
Prof. Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, comments:
“I think this is an important paper which highlights better than before the potential value to health of higher dietary fibre intake. However, as with the vast majority of nutritional data, most of the evidence comes from observational studies and one has to be cautious about conclusions reached given the unavoidable biases they contain. That noted, this paper importantly also includes risk factor data from trials and the reductions in weight and other known causal risk factors such as blood pressure, cholesterol, etc seen with higher fibre (whole grain) diets, although modest do support the overall findings linking more fibre in the diet to less heart disease, diabetes, cancers, and potentially longer life. So I tend to believe the overall findings are directionally true and so concur with the authors conclusions when they write “recommendations to increase dietary fibre intake and to replace refined grains with whole grains is expected to benefit human health.” ”
Conflict of interest statement: None.
Prof Kevin Whelan, Professor of Dietetics, King’s College London, comments:
“The study published by Reynolds and colleagues draws together all previous studies investigating fibre and human health, and importantly they include both observational studies and randomised controlled trials. The researchers were able to look at 185 observational studies which recorded what people were eating in their everyday lives and then related that to whether they go on to develop disease over time – in total for 135 million person years. The researchers also looked at the results of 58 clinical trials of fibre, whereby people were given new diets and to investigate the effect on health and the results are able to show cause and effect relationships.
“The greatest reduction in risk of disease was when dietary fibre intake was between 25-29 g per day. Dietary recommendations in the UK are that the general public should eat 30 g per day of fibre, and so this national recommendation is consistent with the findings of this latest analysis. The challenge is that many people in the UK do not eat this amount of fibre. The major sources of fibre in the UK diet are cereals (bread, pasta, rice, breakfast cereal), vegetables and fruit. People should consider ways of increasing fibre intake through changing food preparation methods (e.g. not peeling potatoes), switching to wholegrain cereals (wholegrain bread, brown pasta) and replacing sugary snacks with fruits, vegetables, nuts and seeds.
“Importantly this research was able to investigate not only the effect of the total amount of fibre, but also the quality of the fibre. For example, wholegrain fibres were shown to have significant health effects whereas the evidence that low glycaemic index diets were effective were less convincing.”
Conflict of interest statement: “I have received research funding from government agencies such as the Medical Research Council, National Institute of Health Research, charities such as Helmsley Trust, Kenneth Rainin Foundation and Crohn’s and colitis UKL and industry bodies including the Californian Dried Plum Board, Almond Board of California, International Nut and Dried Fruit Council, Nestle and Danone.”