Effects of a slowly fermentable fiber mixture against the background of a high-protein diet on insulin sensitivity and metabolic health in individuals with overweight: a randomized, placebo-controlled trial.
Colin A J van Kalkeren, Thirza van Deuren, Miranda M J Coenjaerds et al.
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In 30 seconds
This 12-week randomized, placebo-controlled trial tested daily potato fiber and sugar beet pectin against maltodextrin in adults with overweight or obesity consuming a high-protein diet. The fiber group included 19 participants and the placebo group 21. Peripheral insulin sensitivity tended to decline with fiber versus placebo (p = 0.081), while whole-body insulin sensitivity significantly decreased (p = 0.034). Fiber also altered substrate oxidation and was associated with increased gut permeability and plasma interleukin-6. Body composition, microbial composition, and measured fecal and circulating metabolites were unchanged.
Key findings
- Whole-body insulin sensitivity decreased significantly with fiber compared with placebo (p = 0.034); peripheral insulin sensitivity showed a nonsignificant tendency to decrease (p = 0.081).
- Fiber mitigated the placebo-group increase in insulin-mediated carbohydrate oxidation (p = 0.027) and decrease in fat oxidation (p = 0.006).
- Fiber prevented an increase in protein oxidation (p = 0.048), but increased colonic gut permeability (p = 0.046) and plasma interleukin-6 (p = 0.025).
- Body composition, microbial composition, and fecal and circulating metabolites remained unchanged.
Why it matters
The findings challenge the assumption that increasing fermentable fiber necessarily improves metabolic health when paired with a high-protein diet. In this trial, the combination was associated with lower insulin sensitivity and changes in substrate oxidation, alongside signals of impaired gut barrier function and inflammation. These outcomes highlight the importance of considering dietary context when evaluating fiber interventions.
What to keep in mind
The trial was small, with 19 participants in the fiber group and 21 in the placebo group, and lasted 12 weeks. Its findings apply to the tested fiber mixture alongside a high-protein diet.