The effects of SCFAs on glycemic control in humans: a systematic review and meta-analysis.

BACKGROUND: Noncommunicable disease development is related to impairments in glycemic and insulinemic responses, which can be modulated by fiber intake. Fiber's beneficial effects upon metabolic health can be partially attributed to the production of SCFAs via microbial fermentation of fiber in the gastrointestinal tract. OBJECTIVES: We aimed to determine the effects of SCFAs, acetate, propionate, and butyrate on glycemic control in humans. METHODS: The CENTRAL, Embase, PubMed, Scopus, and Web of Science databases were searched from inception to 7 December 2021. Papers were included if they reported a randomized controlled trial measuring glucose and/or insulin compared to a placebo in adults. Studies were categorized by the type of SCFA and intervention duration. Random-effects meta-analyses were performed for glucose and insulin for those subject categories with ≥3 studies, or a narrative review was performed. RESULTS: We identified 43 eligible papers, with 46 studies within those records (n = 913), and 44 studies were included in the meta-analysis. Vinegar intake decreased the acute glucose response [standard mean difference (SMD), -0.53; 95% CI, -0.92 to -0.14; n = 67] in individuals with impaired glucose tolerance or type 2 diabetes and in healthy volunteers (SMD, -0.27; 95% CI, -0.54 to 0.00; n = 186). The meta-analyses for acute acetate, as well as acute and chronic propionate studies, showed no significant effect. CONCLUSIONS: Vinegar decreased the glucose response acutely in healthy and metabolically unhealthy individuals. Acetate, propionate, butyrate, and mixed SCFAs had no effect on blood glucose and insulin in humans. Significant heterogeneity, risks of bias, and publication biases were identified in several study categories, including the acute vinegar glucose response. As evidence was very uncertain, caution is urged when interpreting these results. Further high-quality research is required to determine the effects of SCFAs on glycemic control.

Validation of use of annular once-punched filter paper bloodspot samples for repeat lead testing.

BACKGROUND: Lack of a second sample often precludes the ability to perform repeat lead measurements on filter paper bloodspot samples. We investigated whether annular specimens remaining from once-punched filter paper bloodspot specimens could provide accurate Pb measurements when measurements were scaled for the remainder area relative to the original punch area. METHODS: 50 microl bloodspot specimens were prepared using Pb-spiked EDTA whole blood. After removal of 6 mm punches, bitmap images of the remainder specimens were obtained using a scanner. Image analysis was used to determine the bloodspot area of the remainder sample relative to the area of the original punch. Measurement of Pb for punches and for remainder specimens was performed by ICP-MS. RESULTS: Area-corrected Pb measurements for remainder samples were significantly higher than for the punches, by an average factor of 1.52+/-0.12 (p<0.05, n=28). The difference was due to a discontinuity (an increase) in the per-area Pb at the bloodspot perimeter. Area-corrected results for annular specimens that excluded the perimeter were identical to those of the punch. CONCLUSION: Area-corrected Pb measurement using annular once-punched bloodspot remainder specimens can accurately reproduce lead measurements obtained from the original punch when the bloodspot perimeter area is excluded.