Blood sugar ended up lower on a prescribed fiber plan than on metformin in a small trial from China, though only 12 of the 48 adults in it took the drug. The Frontiers in Microbiology paper appeared in early October after the volunteers were followed for 84 days.
All of them had a new type 2 diabetes diagnosis and extra weight. Researchers at Henan Provincial People’s Hospital assigned them by chance to fiber formulas with dietitian guidance and no diabetes medication (36 people), or to metformin alone (12 people).
By day 84 the fiber group averaged an HbA1c of 6.32% against 6.74% on metformin, a real gap from a trial too small to name a winner.
The Fiber Group Finished With A Lower HbA1c And A Lower BMI
HbA1c is a blood test that reflects average blood sugar over roughly the past three months. After adjusting for starting values, the fiber group’s reading was 6.32% and the metformin group’s was 6.74%, a difference of 0.42 points. Body mass index split wider, 28.42 against 30.22.
Fasting glucose was lower on the fiber plan at days 28 and 56 but showed no significant difference by day 84. Continuous glucose monitors also recorded smaller swings through the day in the fiber group, according to News-Medical’s trial coverage. Triglycerides and total body fat came out lower too.
Only 12 People Took The Drug, So The Comparison Is Lopsided
The write-ups of the trial point to several limits worth knowing before anyone repeats the headline:
- Randomization ran 3 to 1, so 36 adults went to the fiber plan and 12 to metformin. In all, 46 finished.
- One hospital ran the trial, and it was open-label, meaning all participants knew which treatment they were getting.
- The “diet” was prescribed fiber formulas built from ingredients such as inulin, resistant dextrin and konjac gum, along with wheat and oat fiber. A normal menu of beans and oats wasn’t what got tested.
- The fiber group also took in less energy overall. The report says that may explain part of the weight difference.
- Summaries of the trial leave out the metformin dose, because treating doctors set it.
The HbA1c result barely clears the usual cutoff for statistical significance (p = 0.042). The ranges around the two averages overlap slightly. The BMI result is much firmer, with p below 0.001. Coverage of the trial also leaves out who paid for it.
Gut Bacteria Shifted Within 28 Days On The Fiber Plan
Researchers sequenced 184 stool samples collected over the course of the trial. By day 28 the fiber group’s bacterial community looked different, with more Bifidobacterium and Lactobacillus and less Bilophila wadsworthia, a bacterium linked to chronic inflammation in Medical News Today’s report. The metformin group showed no significant change in overall bacterial makeup, though the authors say small shifts can’t be ruled out.
Adults whose stool acetate rose saw bigger HbA1c drops at days 28 and 56. Acetate is a short-chain fatty acid made when gut bacteria ferment fiber. The finding rests on small exploratory subgroups that need independent confirmation. GLP-1 levels weren’t measured, so the team couldn’t test how acetate or hydrogen sulfide might actually act on blood sugar.
Two Clinicians Outside The Study Say Food And Medicine Work Together
Mir Ali, a bariatric surgeon at MemorialCare Surgical Weight Loss Center, wasn’t surprised. “This is just supporting evidence that it can dramatically make a difference,” he said. He’d like larger studies that compare fiber types, such as fruits against vegetables.
Monique Richard, a registered dietitian nutritionist, cautioned against reading the result as fiber beating the drug. “Food and medication are not competing strategies, but often critically important complementary parts of care,” she said. Ali and Richard had no role in the trial.
Don’t Stop Metformin Or Change Your Plan Without Your Doctor
Volunteers had a recent diagnosis and a starting HbA1c between 6.5% and under 9%. Findings from that group say little about people with long-standing diabetes or higher numbers. The CDC’s diabetes treatment page says a healthy diet, a healthy weight and regular physical activity can all help with managing blood sugar.
Eighty-four days is a short window. EMJ’s trial summary calls for larger groups and longer follow-up to judge how long the benefits last. Until those results exist, anyone curious about adding fiber products should ask their care team about amounts first.
For more on gut health and blood sugar, see our earlier pieces on gut bacteria linked to type 2 diabetes risk and on ultra-processed meals and insulin response.
