The Fibre Sweet Spot: 25 to 29 Grams a Day
The finding: Across nearly 135 million person-years of data, the highest fibre eaters had 15% to 30% lower all-cause mortality. The clearest benefit landed at 25 to 29 g a day, and the curve kept improving beyond that.
What they did
This was a series of systematic reviews and meta-analyses rather than a single study, commissioned in part for the World Health Organization and published in The Lancet. The team pulled together 185 prospective observational studies and 58 randomised controlled trials involving 4,635 adults, covering just under 135 million person-years of follow-up.
They deliberately excluded studies of people who already had a chronic disease, and excluded weight-loss and supplement trials, so what remains is about ordinary dietary fibre in people who were well. Certainty was graded with GRADE, and robustness tested with sensitivity analyses, meta-regression and dose-response modelling.
What they found
- Highest fibre eaters against lowest: 15% to 30% lower all-cause and cardiovascular mortality, and lower incidence of coronary heart disease, stroke, type 2 diabetes and colorectal cancer.
- The randomised trials independently showed significantly lower body weight, systolic blood pressure and total cholesterol at higher fibre intakes.
- Risk reduction was greatest between 25 g and 29 g of fibre a day.
- The dose-response curves suggested going higher still could confer even greater benefit.
- Whole grain intake showed the same pattern.
- Glycaemic index and glycaemic load showed much weaker associations, so fibre and whole grains carried the signal.
The authors concluded that the striking dose-response evidence indicates the relationships to several non-communicable diseases could be causal. That is strong language for nutrition epidemiologists, and their reasoning was the shape of the curve: more fibre, less risk, steadily and smoothly, with randomised trials independently confirming plausible mechanisms.
What this means for you
Most Australian adults eat well under 25 g a day. The target from this review is 25 to 29 g, and the curve says more is better rather than worse.
Where that fibre came from in these studies was food: whole grains, legumes, vegetables, fruit. Supplement trials were specifically excluded from the analysis, so this is evidence for a high-fibre diet, with a fibre supplement as a practical way to help close a real gap in it.
If you are increasing fibre, do it gradually and drink more water. Going from 12 g to 30 g overnight is uncomfortable, and people who try it usually give up in the first week. Add 5 g, hold for a few days, then add again.
The study
Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet. 2019 Feb 2;393(10170):434-445.
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General information only. This is a summary of published research, not a therapeutic claim and not medical advice. A result found in a trial population is not the same as a product doing that for you. Always read the label and follow the directions for use. If you have a health condition or take medication, check with your health practitioner before use.
