Fibre-focused diet counselling barely moved heart risk in a diabetes trial
Six months of dietitian sessions aimed at a high-fibre diet nudged diet quality but left estimated 10-year cardiovascular risk, HbA1c, cholesterol and blood pressure essentially unchanged versus standard care.
Advice to eat more fibre is one of the least controversial things in nutrition. The observational case is strong, and it underpins dietary guidance for people with type 2 diabetes, who face elevated cardiovascular risk. What is far less clear is how much a realistic dose of that advice — a handful of sessions with a dietitian — actually changes measured risk over months. A new randomised trial from the Netherlands put a number on it, and the number is small [s1].
What the trial did
Researchers randomised 121 adults with type 2 diabetes to either dietary counselling or standard care [s1]. The participants averaged 67 years of age (SD 8.7), 68% were men, and mean BMI was 27.8 kg/m² [s1]. Sixty-one were assigned to the counselling arm and 60 to standard care [s1]. The intervention was hands-on: four to seven individual sessions with a dietitian over six months, aimed specifically at raising fibre intake and improving overall diet quality [s1].
The primary outcome was a composite score estimating 10-year cardiovascular risk [s1]. Secondary outcomes included diet quality measured by the Dutch Healthy Eating Index-2015 (the DHD15-index), HbA1c, LDL-cholesterol, blood pressure, body weight and medication use [s1].
The numbers
The counselling did shift eating, modestly. The DHD15 diet-quality score, which started at 115 (SD 26) and was similar across groups at baseline, improved by 4.5 points (95% CI −0.2 to 9.1) in the intervention group relative to control — an improvement that did not reach statistical significance [s1].
On the outcome the trial was built around, there was essentially nothing. The change in estimated 10-year cardiovascular risk did not differ between the groups: −0.1% (95% CI −0.2 to 0.1) [s1]. The secondary cardiometabolic markers told the same story. Between-group differences in the change over time were −1.1 mmol/mol for HbA1c (95% CI −4.4 to 2.3), 0.0 mmol/l for LDL-cholesterol (95% CI −0.2 to 0.3), −1 mmHg for blood pressure (95% CI −6 to 4) and −0.1 kg for body weight (95% CI −1.2 to 1.1) [s1]. Medication use did not differ either [s1].
The authors' own summary is blunt: counselling slightly improved adherence to a high-quality, fibre-rich diet but did not significantly affect cardiometabolic health or medication use [s1]. None of the secondary confidence intervals excluded a null effect, and several were centred close to zero — the LDL-cholesterol difference was exactly 0.0 mmol/l, and body weight moved by a tenth of a kilogram [s1]. Taken together, the pattern is not a marginally missed benefit but a flat result across every cardiometabolic measure the trial recorded.
Why a null here is worth reading carefully
This is not evidence that fibre does not matter. It is evidence about what a specific, realistic counselling programme achieved over six months in a specific population — older, mostly male, only modestly overweight, and starting from a fairly high baseline diet-quality score of 115 [s1]. When people already eat reasonably well, there is less room for advice to move the needle, and a change of 4.5 points in a diet-quality index is small [s1].
That gap between the observational promise of fibre and a flat trial result is a recurring pattern in nutrition science. The large evidence base linking higher fibre intake to lower disease risk rests mainly on prospective cohort studies and on trials of biomarkers rather than of hard cardiovascular events; a 2019 series of systematic reviews and meta-analyses that shaped fibre recommendations drew on exactly that kind of evidence [s2]. Translating those associations into measured risk reduction through brief counselling is a much harder test, and this trial suggests the counselling itself may be the weak link — behaviour changed only a little, so downstream markers changed less.
The limits cut both ways. Six months is short, the trial was not large, and a composite risk score is a model, not an event count — it cannot capture benefits that take years to appear or that a 121-person study is underpowered to detect. A null on a surrogate is not proof of no effect.
What to watch
The practical read is narrow but useful: a few dietitian sessions focused on fibre produced a small change in what people ate and no measurable change in their cardiometabolic risk over six months [s1]. Whether more intensive support, a longer horizon, or people with worse baseline diets would show something is exactly what this trial cannot answer. The broader question — how much of fibre's observational benefit survives a randomised test with hard endpoints — remains open.
This article is informational and does not constitute medical advice.
Sources
- [s1] Cardiometabolic health effects of dietary counselling on a high-quality, fibre-rich diet in adults with type 2 diabetes: a randomised controlled trial. British Journal of Nutrition, 10 April 2026. https://doi.org/10.1017/s0007114526107041
- [s2] Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet, 10 January 2019. https://doi.org/10.1016/S0140-6736(18)31809-9
Sources
- Cardiometabolic health effects of dietary counselling on a high-quality, fibre-rich diet in adults with type 2 diabetes: a randomised controlled trial — British Journal of Nutrition , April 10, 2026
- Carbohydrate quality and human health: a series of systematic reviews and meta-analyses — The Lancet , January 10, 2019
More on
Glycaemic index: does choosing low-GI foods actually help?
In a tightly controlled feeding trial, swapping high-GI for low-GI carbohydrate inside a healthy diet did not improve insulin sensitivity, cholesterol or blood pressure. The wider evidence rates the GI case as weak.
Is the carnivore diet safe? What the evidence can and cannot show
No long-term trial has tested an all-meat diet. The best direct data is a self-reported survey where people felt better but ran markedly high LDL cholesterol — the signal that should give pause.
Is honey healthier than sugar? What controlled trials actually show
Honey and table sugar are both free sugars with almost identical calories. Trials hint at small metabolic differences in honey's favour, but the certainty is low and honey is still added sugar to be limited.
Is the sugar in fruit bad for you? What the diabetes data show
Whole fruit and fruit juice behave oppositely for type 2 diabetes risk, and a trial that told newly diagnosed patients to eat less fruit found no benefit at all.