Can a fibre supplement fix your blood sugar?
A Fibre Supplement for Prediabetes Didn't Work on Average. For Some People, It Did
· By Anthony Falcone
Verdict: Too early to tell. Not on average. Six months of a high-dose fibre supplement didn't improve blood sugar more than standard advice. Some subgroups did improve, which hints at personalised nutrition — but that finding still needs to be confirmed.
What the researchers tested
Adults with prediabetes were randomly assigned to standard diet and exercise advice, or to the same plus a mixed fibre supplement — wheat bran, oat bran, resistant starch, inulin and other prebiotic fibres — at 15 g with each meal.
659 people completed the six months. No adverse events were reported.
What they found
The main result was negative: no difference between groups in HbA1c (long-term blood sugar) or any other main outcome.
In an analysis done afterwards, the team sorted participants into four groups by age, weight, blood sugar and insulin function. Fibre improved blood-sugar control in two of the four groups, and those were the groups whose gut bacteria responded to the fibre.
They then trained a computer model on gut-microbiome data to predict who would benefit. It's an interesting step towards personalised nutrition, not something you can use yet.
What this means for you
- Fibre is still good for you — this trial tested a high-dose supplement on top of advice, for one outcome, over six months.
- Don't expect a fibre powder to fix blood sugar by itself. Responses differ from person to person.
- If you increase fibre, do it gradually and from varied foods; 45 g a day is far more than most people eat.
How much to trust it
- The positive subgroup findings came from analysis done after the trial, which is weaker evidence than the main result.
- Participants knew which group they were in (open-label).
- All participants were from eastern China, and COVID-19 disrupted the planned longer follow-up.
The study
Song D, Feng G, Ma Y, Shi Y, et al. Gut microbiome predicts personalized responses to dietary fiber in prediabetes: a randomized, open-label trial. Nature Communications, 2025. doi.org/10.1038/s41467-025-66498-x
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