You might have noticed claims in the media in the last few days that

New research conducted by Deloitte Access Economics and Nutrition Research Australia shows that if every New Zealand adult adds three serves of high fibre grain food to their daily diet, it could save the economy an estimated $607 million a year in reduced healthcare costs and lost productivity, and potentially avert 34,000 new cases of cardiovascular disease and 68,000 new cases of type 2 diabetes.

This is from a report (dae-nz-fibre-economics) that Deloitte produced for Kellogg’s. Industry funding was a conflict of interest properly reported by media. We have a rough rule of thumb around this – when industry funds basic research in labs – experiments – that’s not necessarily a bad thing, because science always needs funding, and we want answers to questions. When industry funds reviews and modelling, these are more likely to be subject to cherry-picking to favour the sponsor – they are questions of interpretation, so the risk of bias is higher.

The causes of disease and mortality that grain fibre is supposed to be able to prevent are cardiovascular disease and type 2 diabetes.

Based on data from published meta-analyses, the number of cases averted was estimated by assuming that a one-gram increase in grain fibre reduces the risk of CVD by 1.1% and T2D by 2.5% (Threapleton, 2013; InterAct Consortium, 2015).

We took a closer look at the evidence used to calculate the larger of the two benefits, that for type 2 diabetes. This was the EPIC-InterAct study and meta-analysis; the EPIC-InterAct study was a multicentre European observational study that didn’t find a protective association for grain fibre once adjusted for BMI (but there are some interesting details we’ll discuss later), so the authors added a meta-analysis (a statistical method that pools all available studies world-wide) that did find a protective association with grain fibre.[1]

“However, the findings from our updated meta-analysis of prospective studies do support an inverse association between total fibre and cereal fibre intake and risk of type 2 diabetes, with a 9% and 25% lower RR per 10 g/day, respectively, independent of BMI.”

So an extra 10g of grain fibre reduces your risk of type 2 diabetes by 25%. Or does it? Actually, it depends on where you live.

There are many countries in EPIC-Interact without a protective association between grain fibre and type 2 diabetes, including France with a non-significant HR of 1.72 (that’s 72% worse). Another exception is the UK with a non-significant HR of 0.74 (26% better).

What are the differences in these populations? The French cohorts, for some reason, are all 100% female, which isn’t the case for any other country. And the largest of the two UK cohorts is EPIC-Oxford. “The majority of participants recruited by the EPIC Oxford (UK) centre consisted of vegetarian and “health conscious” volunteers from England, Wales, Scotland, and Northern Ireland”.[2] So these health conscious volunteers are probably being compared with people with lower fibre intakes in the less health-conscious UK cohort.

Sweden always interests us because one of their two cohorts is the Malmö Diet and Cancer Study, which unlike the usual observational diet studies in this, or any other meta-analysis, uses the more accurate 7-day food diary for all subjects, and in Sweden the HR is a more reasonable 0.96. So less confounding by conscientiousness and more accurate diet recall tends to minimize the cereal fibre and type 2 diabetes association. If cereal fibre prevented type 2 diabetes in any important or unique way, it should probably show up in most of these populations, not just a few.

What about the other countries in the meta-analysis? Most of the weighty studies in favour of fibre for type 2 diabetes prevention in the EPIC-Interact meta-analysis come from the USA. There are two important facts about the USA – low fibre intakes are lower than they are anywhere else (so basically a high intake of deep fried food, white breads, and sweetened soda in these low-fibre groups), and conscientiousness is an identifiable confounding factor in many populations. For example, the Nurses’ Health Study and Health Professionals’ Follow-up Study; here we have the populations not only given the most advice about fibre being healthy, but also given the job of passing it on to the other US populations. In other words, grain fibre – like red meat – is one of the signifiers separating conscientious Americans from other Americans (it’s harder to eat fruit and vegetables without their fibre, and vegetables in the US includes fried potatoes). It’s almost a class distinction.

Closer to home, there are 3 Australian studies, two small ones with protective associations between grain fibre and type 2 diabetes (smaller studies have less weight in a meta-analysis) and a large one, Hodge 2004, with none.[3] However Hodge 2004 finds that white bread is associated with type 2 diabetes, and that lower GI carbs, including sugar, aren’t.

White bread in Australia is so bad that even sugar looks good by comparison.

Does it follow that putting a few grams of bran in white bread will make it safe, or even good for you? Why not just say “avoid white bread”? This would definitely be our advice! Anyway, if fibre isn’t associated with type 2 diabetes in a fairly large sample of Australians, who tend to have fairly high fibre intakes anyway (by OECD standards), do Kiwis still need to take their lead from the USA?

“The mean±SD fibre intake in the [European] subcohort was 22.9± 6.2 g/day (ranging from 19.9 g/day in Sweden to 25.2 g/day in Denmark; data not shown).”[1]

These figures for European countries are very similar to the averages for New Zealand – 22.8 g/day for men and 17.9 g/day for women.

Germany (7.40%) and Denmark (7.20%) have higher diabetes prevalence rates than Sweden (4.70%).  USA’s mean total fibre intake is 16.1 g/day and diabetes prevalence is 10.80%. This would suggest that there is a suboptimal fibre intake, or perhaps just a protective effect of the real food, higher fat diets eaten in a place like Sweden, where (in Malmö) dairy fat has a protective association with type 2 diabetes, total fat has a protective association with CVD mortality in men, and fibre is protective against heart attacks only in combination with saturated fat (most of this is grain fibre in Malmö, probably from rye bread).[4,5] Sucrose – sugar – is the only nutrient/food/ingredient significantly associated with increased heart disease risk in Malmö.[6]  Its effect on the lipid profile is to increase triglycerides.[7]

Participants who consumed >15 % of their energy intake (E%) from sucrose showed a 37 (95 % CI 13, 66) % increased risk of a coronary event compared with the lowest sucrose consumers (<5 E%) after adjusting for potential confounders. The association was not modified by the selected lifestyle factors.

There are no nutrients unique to grains. But some grain fibres, especially oat bran, are a very good source of silicon, a mineral which might be more important for cardiovascular health than is currently recognised.[8] Other good sources of silicon are mineral water (the higher the total dissolved solids, the higher the silicon content is likely to be), green beans (especially) and other crunchy fibrous vegetables, bone broth, red wine and beer, and some herb teas, especially horsetail, oatstraw, and nettle. Oat bran is low in digestible carbohydrate and could definitely be included in the LCHF diet if anyone thought this necessary (it makes a great binder for mince patties).

The push from Kelloggs is to increase fibre by eating more grains and cereals – this is conflating any benefit of fibre with the effect of starch (and sugar if we’re talking breakfast cereals). Indeed fibre might be healthful but if you get it by adding extra bread and breakfast cereal what does that mean? for example, from EPIC-Netherlands:[9]

Dietary GL was associated with an increased diabetes risk after adjustment for age, sex, established diabetes risk factors, and dietary factors [hazard ratio (HR) per SD increase: 1.27; 95% CI: 1.11, 1.44; P < 0.001] [corrected]. GI tended to increase diabetes risk (HR: 1.08; 95% CI: 1.00, 1.17; P = 0.05). Dietary fiber was inversely associated with diabetes risk (HR: 0.92; 95% CI: 0.85, 0.99; P < 0.05), whereas carbohydrate intake was associated with increased diabetes risk (HR: 1.15; 95% CI: 1.01, 1.32; P < 0.05). Of the carbohydrate subtypes, only starch was related to increased diabetes risk [HR: 1.25 (1.07, 1.46), P < 0.05]. All associations became slightly stronger after exclusion of energy misreporters.

And don’t forget the PURE study, as well as the Czech ecological analyses (below) – there are protective effects from moderate amounts of high fibre foods, but replacing fat with lots of carbohydrate is overall associated with a worsened metabolic profile and higher mortality.[10, 11]

The aim of this study was a large-scale ecological analysis of nutritional and other environmental factors potentially associated with the incidence of cardiovascular diseases (CVDs) in the global context. Indicators of CVDs from 158 countries were compared with the statistics of mean intake (supply) of 60 food items between 1993 and 2011, obesity rates, health expenditure and life expectancy. This comparison shows that the relationship between CVD indicators (raised blood pressure, CVD mortality, raised blood glucose) and independent variables in the global context is influenced by various factors such as short life expectancy, religiously conditioned dietary customs, the imprecision of some statistics and undernutrition. However, regardless of the statistical method used, the results always show very similar trends and identify high carbohydrate consumption (mainly in the form of cereals and wheat in particular) as a dietary factor most consistently associated with the risk of CVDs. These findings are in line with the changing view of the causes of CVDs.

From this evidence, it might be better to get the fibre from the low-starch foods; but if you do eat grains (not everyone is or needs to be low-carb), eating only whole grains, i.e. grains that you can see are whole or minimally broken, in relatively small amounts, and avoiding refined grains as far as possible is the pattern associated with most benefit.

The Bottom line: there are almost certainly people at higher risk of type 2 diabetes and cardiovascular disease because their diets are too dependent on refined and processed carbohydrate foods, especially sugars and grains. Their risk would indeed be lower if they replaced these with whole grains – brown rice, barley, oats and so on. This may be due in part to the fibre content, but it may also be due to the slower release of glucose and thus healthier insulin response to a grain when it hasn’t been powdered; fibre in a powdered grain doesn’t do much to reduce its impact. Yer dreamin if you think that just adding bran to processed carbs – which is what Kellogg’s products do – is going to make an impact on disease rates. Eating whole foods instead of food products might give us a chance.

For people with carbohydrate intolerance, grains are too carbohydrate-dense a food to consume in any quantity, but other fibre-rich foods are available to substitute.

However, to say that high-fibre diets are better is a generalisation – the benefits of fibre require the cooperation of gut bacteria and the gut, and quite a few people who look to diet to improve their health find that lower-fibre diets such as FODMAP exclusion diets and occasionally even zero-carb carnivore diets give significant improvement where high-fibre diets fail.

The What The Fat? diet is high-fibre because fibre increases satiety and there is some evidence for other health benefits, but fibre isn’t necessarily something there should be a bulk ruling about.

P.S. Ironically, when the Herald ran a news story on the Deloitte/Kellogg’s report, the high fibre success story they spoke to was a low(er) carber! There are only a couple of slices of brown bread in this story.

References

[1] The InterAct Consortium. Dietary fibre and incidence of type 2 diabetes in eight European countries: the EPIC-InterAct Study and a meta-analysis of prospective studies. Diabetologia. 2015;58(7):1394-1408. doi:10.1007/s00125-015-3585-9.ghb
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4472947/

[2] The InterAct Consortium, Langenberg C, Sharp S, et al. The InterAct Project: An Examination of the Interaction of Genetic and Lifestyle Factors on the Incidence of Type 2 Diabetes in the EPIC Study. Diabetologia. 2011;54(9):2272-2282. doi:10.1007/s00125-011-2182-9.

[3] Hodge AM, English DR, O’Dea K, Giles GG. Glycemic index and dietary fiber and the risk of type 2 diabetes. Diabetes Care. 2004;27:2701–2706. doi: 10.2337/diacare.27.11.2701

[4] Wallström P, Sonestedt E, Hlebowicz J, et al. Dietary Fiber and Saturated Fat Intake Associations with Cardiovascular Disease Differ by Sex in the Malmö Diet and Cancer Cohort: A Prospective Study. Obukhov AG, ed. PLoS ONE. 2012;7(2):e31637.
doi:10.1371/journal.pone.0031637
[5] Leosdottir M, Nilsson PM, Nilsson JA, Månsson H, Berglund G. Dietary fat intake and early mortality patterns–data from The Malmö Diet and Cancer Study. J Intern Med. 2005 Aug;258(2):153-65. link

[6] Warfa K, Drake I, Wallström P, Engström G, Sonestedt E. Association between sucrose intake and acute coronary event risk and effect modification by lifestyle factors: Malmö Diet and Cancer Cohort Study. Br J Nutr. 2016 Nov;116(9):1611-1620. Epub 2016 Oct 24.

[7] Sonestedt E, Hellstrand S, Schulz C-A, et al. The Association between Carbohydrate-Rich Foods and Risk of Cardiovascular Disease Is Not Modified by Genetic Susceptibility to Dyslipidemia as Determined by 80 Validated Variants. Müller M, ed. PLoS ONE. 2015;10(4):e0126104. doi:10.1371/journal.pone.0126104.

[8] Loeper J, et al. Study of fatty acids in atheroma induced in rabbits by an atherogenic diet with or without silicon IV treatment . Life Sciences 1988, 42:2105-2112.

[9] Sluijs I, van der Schouw YT, van der A DL, Spijkerman AM, Hu FB, Grobbee DE, Beulens JW. Carbohydrate quantity and quality and risk of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition-Netherlands (EPIC-NL) study. Am J Clin Nutr. 2010 Oct;92(4):905-11. doi: 10.3945/ajcn.2010.29620. Epub 2010 Aug 4.

[10] Dehghan M, Mente A2, Zhang X, et al. Prospective Urban Rural Epidemiology (PURE) study investigators. Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet. 2017 Nov 4;390(10107):2050-2062. doi: 10.1016/S0140-6736(17)32252-3. Epub 2017 Aug 29.

[11] Grasgruber P, Cacek J, Hrazdíra E, Hřebíčková S, Sebera M. Global Correlates of Cardiovascular Risk: A Comparison of 158 Countries. Preprints 2018, 2018020066 (doi: 10.20944/preprints201802.0066.v1).
https://www.preprints.org/manuscript/201802.0066/v1