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.
In this study, a fiber supplement combined with a high-protein diet led to a significant decrease in whole-body insulin sensitivity compared to placebo. This suggests potential adverse effects on metabolic health that warrant further research.
Where it sits
this study against the rest of the dihexa corpusSummary and findings
This study evaluated the effects of a potato fiber/sugar beet pectin supplement on metabolic health in adults with overweight/obesity over 12 weeks. The trial involved 19 participants receiving the fiber supplement and 21 receiving a maltodextrin placebo, both on a high-protein diet. The findings indicated a significant decrease in whole-body insulin sensitivity in the fiber group compared to placebo.
Abstract
The gut microbiota ferments dietary fibers, producing short-chain fatty acids (SCFA). Enhanced SCFA production in the distal colon has been linked to improved cardiometabolic health. However, most fibers are fermented proximally, resulting in increased protein fermentation distally, producing metabolites putatively harmful to metabolic health. This 12-week randomized, placebo-controlled trial aimed to improve metabolic health through increasing distal SCFA production while inhibiting proteolytic fermentation using a fiber supplement that increased distal SCFA production <i>in vitro</i>. We assessed the effects of daily potato fiber/sugar beet pectin supplementation (fiber, <i>n</i> = 19) versus maltodextrin (placebo, <i>n</i> = 21), both added to a high-protein diet (25E% protein, ±45% plant-based), on peripheral insulin sensitivity (IS) in adults with overweight/obesity. Secondary outcomes included tissue-specific IS, body composition, microbial composition and functionality, substrate metabolism, and gut permeability. Peripheral IS tended to decrease after fiber supplementation compared to placebo (<i>p</i> = 0.081), while whole-body IS significantly decreased (<i>p</i> = 0.034). Fiber mitigated the increase in insulin-mediated carbohydrate oxidation (<i>p</i> = 0.027) and decrease in fat oxidation (<i>p =</i> 0.006) that occurred in the placebo group. Additionally, fiber prevented an increase in protein oxidation (<i>p</i> = 0.048), while increasing colonic gut permeability (<i>p</i> = 0.046) and plasma interleukin-6 (<i>p</i> = 0.025). Body composition, microbial composition, and fecal and circulating metabolites remained unchanged. In conclusion, fibers combined with a high-protein diet reduced (peripheral) IS and decreased metabolic flexibility compared to placebo. Reduced protein oxidation after fiber may reflect diminished amino acid bioavailability. Additionally, coadministration of fiber and protein may compromise gut barrier function and inflammatory responses. More research investigating the interplay between dietary fibers and proteins is needed.
Background
This study addresses the impact of dietary fibers on metabolic health, particularly in the context of high-protein diets. Previous research has linked short-chain fatty acids (SCFA) produced from fiber fermentation to improved cardiometabolic health. However, the fermentation of fibers can vary, potentially impacting metabolic outcomes. This trial seeks to clarify the effects of a specific fiber supplement on insulin sensitivity and other metabolic markers.
Methods
This was a 12-week randomized, placebo-controlled trial involving adults with overweight/obesity. A total of 40 participants were enrolled, with 19 receiving potato fiber/sugar beet pectin and 21 receiving maltodextrin as a placebo, both in conjunction with a high-protein diet. The primary outcome was peripheral insulin sensitivity, while secondary outcomes included body composition, microbial composition, and gut permeability.
Results
Whole-body insulin sensitivity significantly decreased in the fiber group compared to placebo, p=0.034. Peripheral insulin sensitivity tended to decrease, p=0.081. The fiber group mitigated the increase in insulin-mediated carbohydrate oxidation, p=0.027, and decreased fat oxidation in the placebo group, p=0.006. Additionally, fiber supplementation led to an increase in colonic gut permeability, p=0.046, and plasma interleukin-6, p=0.025.
Interpretation
The findings suggest that the fiber supplement may negatively impact insulin sensitivity and metabolic flexibility compared to the placebo. While the results are statistically significant, the clinical relevance of the observed changes, particularly in peripheral insulin sensitivity, is uncertain. The small sample size and specific dietary context limit the generalizability of these results, indicating a need for further investigation into the interplay between dietary fibers and proteins.
Key findings
- Whole-body insulin sensitivity significantly decreased, p=0.034.
- Peripheral insulin sensitivity tended to decrease, p=0.081.
- Fiber mitigated the increase in insulin-mediated carbohydrate oxidation, p=0.027.
- Fat oxidation significantly decreased in the placebo group, p=0.006.
- Fiber increased colonic gut permeability, p=0.046.
- Plasma interleukin-6 increased, p=0.025.
Limitations
- small sample size, n=40
- 12-week follow-up too short to assess long-term effects
- specific population may limit generalizability
- no significant changes in body composition or microbial composition