A comparison of the effects of resistant starch types on glycemic response in individuals with type 2 diabetes or prediabetes: A systematic review and meta-analysis.

Background: Type 2 diabetes (T2D) diagnoses are predicted to reach 643 million by 2030, increasing incidences of cardiovascular disease and other comorbidities. Rapidly digestible starch elevates postprandial glycemia and impinges glycemic homeostasis, elevating the risk of developing T2D. Starch can escape digestion by endogenous enzymes in the small intestine when protected by intact plant cell walls (resistant starch type 1), when there is a high concentration of amylose (resistant starch type 2) and when the molecule undergoes retrogradation (resistant starch type 3) or chemical modification (resistant starch type 4). Dietary interventions using resistant starch may improve glucose metabolism and insulin sensitivity. However, few studies have explored the differential effects of resistant starch type. This systematic review and meta-analysis aims to compare the effects of the resistant starch from intact plant cell structures (resistant starch type 1) and resistant starch from modified starch molecules (resistant starch types 2-5) on fasting and postprandial glycemia in subjects with T2D and prediabetes. Methods: Databases (PubMed, SCOPUS, Ovid MEDLINE, Cochrane, and Web of Science) were systematically searched for randomized controlled trials. Standard mean difference (SMD) with 95% confidence intervals (CI) were determined using random-effects models. Sub-group analyses were conducted between subjects with T2D versus prediabetes and types of resistant starch. Results: The search identified 36 randomized controlled trials (n = 982), 31 of which could be included in the meta-analysis. Resistant starch type 1 and type 2 lowered acute postprandial blood glucose [SMD (95% CI) = -0.54 (-1.0, -0.07)] and [-0.96 (-1.61, -0.31)]. Resistant starch type 2 improved acute postprandial insulin response [-0.71 (-1.31, -0.11)]. In chronic studies, resistant starch type 1 and 2 lowered postprandial glucose [-0.38 (-0.73, -0.02), -0.29 (-0.53, -0.04), respectively] and resistant starch type 2 intake improved fasting glucose [-0.39 (-0.66, -0.13)] and insulin [-0.40 (-0.60, -0.21)]. Conclusion: Resistant starch types 1 and 2 may influence glucose homeostasis via discrete mechanisms, as they appear to influence glycemia differently. Further research into resistant starch types 3, 4, and 5 is required to elucidate their effect on glucose metabolism. The addition of resistant starch as a dietary intervention for those with T2D or prediabetes may prevent further deterioration of glycemic control.

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.

The impact of starchy food structure on postprandial glycemic response and appetite: a systematic review with meta-analysis of randomized crossover trials.

BACKGROUND: Starchy foods can have a profound effect on metabolism. The structural properties of starchy foods can affect their digestibility and postprandial metabolic responses, which in the long term may be associated with the risk of type 2 diabetes and obesity. OBJECTIVES: This systematic review sought to evaluate the clinical evidence regarding the impact of the microstructures within starchy foods on postprandial glucose and insulin responses alongside appetite regulation. METHODS: A systematic search was performed in the PUBMED, Ovid Medicine, EMBASE, and Google Scholar databases for data published up to 18 January 2021. Data were extracted by 3 independent reviewers from randomized crossover trials (RCTs) that investigated the effect of microstructural factors on postprandial glucose, insulin, appetite-regulating hormone responses, and subjective satiety scores in healthy participants. RESULTS: We identified 745 potential articles, and 25 RCTs (n = 369 participants) met our inclusion criteria: 6 evaluated the amylose-to-amylopectin ratio, 6 evaluated the degree of starch gelatinization, 2 evaluated the degree of starch retrogradation, 1 studied starch-protein interactions, and 12 investigated cell and tissue structures. Meta-analyses showed that significant reductions in postprandial glucose and insulin levels was caused by starch with a high amylose content [standardized mean difference (SMD) = -0.64 mmol/L*min (95% CI: -0.83 to -0.46) and SMD = -0.81 pmol/L*min (95% CI: -1.07 to -0.55), respectively], less-gelatinized starch [SMD = -0.54 mmol/L*min (95% CI: -0.75 to -0.34) and SMD = -0.48 pmol/L*min (95% CI: -0.75 to -0.21), respectively], retrograded starch (for glucose incremental AUC; SMD = -0.46 pmol/L*min; 95% CI: -0.80 to -0.12), and intact and large particles [SMD = -0.43 mmol/L*min (95% CI: -0.58 to -0.28) and SMD = -0.63 pmol/L*min (95% CI: -0.86 to -0.40), respectively]. All analyses showed minor or moderate heterogeneity (I2 < 50%). Sufficient evidence was not found to suggest how these structural factors influence appetite. CONCLUSIONS: The manipulation of microstructures in starchy food may be an effective way to improve postprandial glycemia and insulinemia in the healthy population. The protocol for this systematic review and meta-analysis was registered in the international prospective register of systematic reviews (PROSPERO) as CRD42020190873.