The impact of slowly digestible and resistant starch on glucose homeostasis and insulin resistance.

PURPOSE OF REVIEW: This review will summarize recent studies assessing the effect of slowly digestible starch (SDS) and resistant starch (RS) on glucose metabolism in healthy, prediabetic or type 2 diabetic adults. RECENT FINDINGS: Currently, a particular interest in starch and its digestibility has arisen, with data showing a positive effect of SDS and RS on the glucose homeostasis of healthy, at-risk, prediabetic and type 2 diabetic patients but research is ongoing. SUMMARY: Carbohydrates (CHO) and especially starch play a major role in the prevention and management of metabolic diseases such as type 2 diabetes (T2D). This largely depends on the quality and the digestibility (rate and extent) of the ingested starchy products, beyond their quantity. SDS have been poorly studied but display a beneficial effect on reducing glucose excursions in healthy and insulin-resistant subjects and a relevant potential to improve glucose control in type 2 diabetic individuals. As for RS, the results appear to be encouraging but remain heterogeneous, depending the nature of the RS and its role on microbiota modulation. Further studies are needed to confirm the present results and investigate the potential complementary beneficial effects of SDS and RS on long-term glucose homeostasis to prevent cardiometabolic diseases.

Multifunctional dietary interventions, low-grade inflammation and cardiometabolic profile: a scoping review.

Background: Growing evidence highlights the significant impact of diet to modify low-grade inflammation closely linked to cardiometabolic profile. Multifunctionnal diets, combining several compounds have been shown to beneficially impact metabolic parameters. Objective: This study synthesizes the knowledge on the impact of RCTs combining dietary multifunctional compounds on low-grade inflammation in humans. We investigate whether the effects of dietary multifunctional interventions on inflammatory markers were parallel to alterations of cardiometabolic parameters. Methodology: We considered both the integrated dietary interventions (ID, i.e. global diets such as Mediterranean, Nordic…) and the dietary interventions based on selected bioactive mix (BM) compounds, in healthy individuals and those at cardiometabolic risk. Out of 221 screened publications, we selected 27 studies: 11 for BM (polyphenols and/or omega-3 fatty acids and/or antioxidants and/or dietary fiber) and 16 for ID (Mediterranean, paleo, Nordic, Dietary Approaches to Stop Hypertension (DASH) diet…). Results: ID studies reflected significant improvements in inflammatory markers (CRP, IL-6, IL-10, IL-1b), concomitantly with beneficial changes in metabolic parameters. In BM studies, pronounced effects on low-grade inflammatory markers were observed, while improvements in metabolic parameters were not consistent. Both types of studies suggested a favorable impact on oxidative stress, a factor closely linked to the inflammatory profile. Conclusion: Our findings showed that multifunctional RCT diets have differential role in managing low-grade inflammation and cardiometabolic health, with a large heterogeneity in explored inflammatory markers. Further research is imperative to elucidate the link between low-grade inflammation and other cardiometabolic risk factors, such as intestinal inflammation or postprandial inflammatory dynamics, aiming to attain a comprehensive understanding of the mechanisms involved in these processes. These future investigations not only have the potential to deepen our insights into the connections among these elements but also pave the way for significant advancements in the prevention and management of conditions related to the cardiovascular and metabolic systems.

Complementary Nutritional Improvements of Cereal-Based Products to Reduce Postprandial Glycemic Response.

High glycemic response (GR) is part of cardiometabolic risk factors. Dietary polyphenols, starch digestibility, and dietary fibers could play a role in modulating GR. We formulated cereal products with high dietary fibers, polyphenols, and slowly digestible starch (SDS) contents to test their impact on the glycemic index (GI) and insulin index (II). Twelve healthy subjects were randomized in a crossover-controlled study to measure the GI and II of four biscuits according to ISO-26642(2010). Two types of biscuits were enriched with dietary fibers and polyphenols and high in SDS, and two similar control biscuits with low levels of these compounds were compared. The subjects consumed 50 g of available carbohydrates from the biscuits or from a glucose solution (reference). Glycemic and insulinemic responses were monitored for 2 h after the start of the consumption. The two enriched biscuits led to low GI and II (GI: 46 ± 5 SEM and 43 ± 4 SEM and II: 54 ± 5 SEM and 45 ± 3 SEM) when controls had moderate GI and II (GI: 57 ± 5 SEM and 58 ± 5 SEM and II: 61 ± 4 SEM and 61 ± 4 SEM). A significant difference of 11 and 15 units between the GI of enriched and control products was obtained. These differences may be explained by the polyphenol contents and high SDS levels in enriched products as well as potentially the dietary fiber content. This study provides new proposals of food formulations to induce beneficial health effects which need to be confirmed in a longer-term study in the context of the SINFONI consortium.

Neurobiology of eating behavior, nutrition, and health.

Eating behavior and food-related decision making are among the most complex of the motivated behaviors, and understanding the neurobiology of eating behavior, and its developmental dynamics, is critical to advancing the nutritional sciences and public health. Recent advances from both human and animal studies are revealing that individual capacity to make health-promoting food decisions varies based on biological and physiological variation in the signaling pathways that regulate the homeostatic, hedonic, and executive functions; past developmental exposures and current life-stage; the food environment; and complications of chronic disease that reinforce the obese state. Eating rate drives increased calorie intake and represents an important opportunity to lower rates of food consumption and energy intake through product reformulation. Understanding human eating behaviors and nutrition in the context of neuroscience can strengthen the evidence base from which dietary guidelines are derived and can inform policies, practices, and educational programs in a way that increases the likelihood they are adopted and effective for reducing rates of obesity and other diet-related chronic disease.

Metabolic signature of 13C-labeled wheat bran consumption related to gut fermentation in humans: a pilot study.

PURPOSE: The aim of this pilot study was to analyze concomitantly the kinetics of production of 13C-labeled gut-derived metabolites from 13C-labeled wheat bran in three biological matrices (breath, plasma, stools), in order to assess differential fermentation profiles among subjects. METHODS: Six healthy women consumed a controlled breakfast containing 13C-labeled wheat bran biscuits. H2, CH4 and 13CO2, 13CH4 24 h-concentrations in breath were measured, respectively, by gas chromatography (GC) and GC-isotope ratio mass spectrometry (GC-IRMS). Plasma and fecal concentrations of 13C-short-chain fatty acids (linear SCFAs: acetate, propionate, butyrate, valerate; branched SCFAs: isobutyrate, isovalerate) were quantified using GC-combustion-IRMS. Gut microbiota composition was assessed by16S rRNA gene sequencing analysis. RESULTS: H2 and CH4 24 h-kinetics distinguished two groups in terms of fermentation-related gas excretion: high-CH4 producers vs low-CH4 producers (fasting concentrations: 45.3 ± 13.6 ppm vs 6.5 ± 3.6 ppm). Expired 13CH4 was enhanced and prolonged in high-CH4 producers compared to low-CH4 producers. The proportion of plasma and stool 13C-butyrate tended to be higher in low-CH4 producers, and inversely for 13C-acetate. Plasma branched SCFAs revealed different kinetics of apparition compared to linear SCFAs. CONCLUSION: This pilot study allowed to consider novel procedures for the development of biomarkers revealing dietary fiber-gut microbiota interactions. The non-invasive assessment of exhaled gas following 13C-labeled fibers ingestion enabled to decipher distinct fermentation profiles: high-CH4 producers vs low-CH4 producers. The isotope labeling permits a specific in vivo characterisation of the dietary fiber impact consumption on microbiota metabolite production. CLINICAL TRIAL REGISTRATION: The study has been registered under the number NCT03717311 at ClinicalTrials.gov on October 24, 2018.

Health relevance of lowering postprandial glycaemia in the paediatric population through diet': results from a multistakeholder workshop.

To summarize current knowledge and gaps regarding the role of postprandial glycaemic response in the paediatric population, a workshop was organized in June 2021 by the European branch of the International Life Science Institute (ILSI). This virtual event comprised of talks given by experts followed by in-depth discussions in breakout sessions with workshop participants. The main pre-specified topics addressed by the workshop organizing committee to the invited speakers and the workshop participants were: (1) the role of glycaemic responses for paediatric health, based on mechanistic insights from animal and human data, and long-term evidence from observational and intervention studies in paediatric populations, and (2) changes in metabolism and changes in dietary needs from infancy to adolescence. Each talk as well as the discussions were summarised, including the main identified research gaps. The workshop led to the consensus on the crucial role on health of postprandial glycaemic response in paediatric population. However, a lack of scientific data has been identified regarding detailed glucose and insulin profiles in response to foods commonly consumed by paediatric populations, as well as a lack of long-term evidence including the need for suitable predictors during childhood and adolescence to anticipate health effects during adulthood.

Microbial liberation of N-methylserotonin from orange fiber in gnotobiotic mice and humans.

Plant fibers in byproduct streams produced by non-harsh food processing methods represent biorepositories of diverse, naturally occurring, and physiologically active biomolecules. To demonstrate one approach for their characterization, mass spectrometry of intestinal contents from gnotobiotic mice, plus in vitro studies, revealed liberation of N-methylserotonin from orange fibers by human gut microbiota members including Bacteroides ovatus. Functional genomic analyses of B. ovatus strains grown under permissive and non-permissive N-methylserotonin "mining" conditions revealed polysaccharide utilization loci that target pectins whose expression correlate with strain-specific liberation of this compound. N-methylserotonin, orally administered to germ-free mice, reduced adiposity, altered liver glycogenesis, shortened gut transit time, and changed expression of genes that regulate circadian rhythm in the liver and colon. In human studies, dose-dependent, orange-fiber-specific fecal accumulation of N-methylserotonin positively correlated with levels of microbiome genes encoding enzymes that digest pectic glycans. Identifying this type of microbial mining activity has potential therapeutic implications.

An approach for evaluating the effects of dietary fiber polysaccharides on the human gut microbiome and plasma proteome.

Increases in snack consumption associated with Westernized lifestyles provide an opportunity to introduce nutritious foods into poor diets. We describe two 10-wk-long open label, single group assignment human studies that measured the effects of two snack prototypes containing fiber preparations from two sustainable and scalable sources; the byproducts remaining after isolation of protein from the endosperm of peas and the vesicular pulp remaining after processing oranges for the manufacture of juices. The normal diets of study participants were supplemented with either a pea- or orange fiber-containing snack. We focused our analysis on quantifying the abundances of genes encoding carbohydrate-active enzymes (CAZymes) (glycoside hydrolases and polysaccharide lyases) in the fecal microbiome, mass spectrometric measurements of glycan structures (glycosidic linkages) in feces, plus aptamer-based assessment of levels of 1,300 plasma proteins reflecting a broad range of physiological functions. Computational methods for feature selection identified treatment-discriminatory changes in CAZyme genes that correlated with alterations in levels of fiber-associated glycosidic linkages; these changes in turn correlated with levels of plasma proteins representing diverse biological functions, including transforming growth factor type ß/bone morphogenetic protein-mediated fibrosis, vascular endothelial growth factor-related angiogenesis, P38/MAPK-associated immune cell signaling, and obesity-associated hormonal regulators. The approach used represents a way to connect changes in consumer microbiomes produced by specific fiber types with host responses in the context of varying background diets.

CGMS and Glycemic Variability, Relevance in Clinical Research to Evaluate Interventions in T2D, a Literature Review.

Glycemic variability (GV) appears today as an integral component of glucose homeostasis for the management of type 2 diabetes (T2D). This review aims at investigating the use and relevance of GV parameters in interventional and observational studies for glucose control management in T2D. It will first focus on the relationships between GV parameters measured by continuous glucose monitoring system (CGMS) and glycemic control and T2D-associated complications markers. The second part will be dedicated to the analysis of GV parameters from CGMS as outcomes in interventional studies (pharmacological, nutritional, physical activity) aimed at improving glycemic control in patients with T2D. From 243 articles first identified, 63 articles were included (27 for the first part and 38 for the second part). For both analyses, the majority of the identified studies were pharmacological. Lifestyle studies (including nutritional and physical activity-based studies, N-AP) were poorly represented. Concerning the relationships of GV parameters with those for glycemic control and T2D related-complications, the standard deviation (SD), the coefficient of variation (CV), the mean blood glucose (MBG), and the mean amplitude of the glycemic excursions (MAGEs) were the most studied, showing strong relationships, in particular with HbA1c. Regarding the use and relevance of GV as an outcome in interventional studies, in pharmacological ones, SD, MAGE, MBG, and time in range (TIR) were the GV parameters used as main criteria in most studies, showing significant improvement after intervention, in parallel or not with glycemic control parameters' (HbA1c, FBG, and PPBG) improvement. In N-AP studies, the same results were observed for SD, MAGE, and TIR. Despite the small number of N-AP studies addressing both GV and glycemic control parameters compared to pharmacological ones, N-AP studies have shown promising results on GV parameters and would require more in-depth work. Evaluating CGMS-GV parameters as outcomes in interventional studies may provide a more integrative dimension of glucose control than the standard postprandial follow-up. GV appears to be a key component of T2D dysglycemia, and some parameters such as MAGE, SD, or TIR could be used routinely in addition to classical markers of glycemic control such as HbA1c, fasting, or postprandial glycemia.

Evaluating microbiome-directed fibre snacks in gnotobiotic mice and humans.

Changing food preferences brought about by westernization that have deleterious health effects1,2-combined with myriad forces that are contributing to increased food insecurity-are catalysing efforts to identify more nutritious and affordable foods3. Consumption of dietary fibre can help to prevent cardiovascular disease, type 2 diabetes and obesity4-6. A substantial number of reports have explored the effects of dietary fibre on the gut microbial community7-9. However, the microbiome is complex, dynamic and exhibits considerable intra- and interpersonal variation in its composition and functions. The large number of potential interactions between the components of the microbiome makes it challenging to define the mechanisms by which food ingredients affect community properties. Here we address the question of how foods containing different fibre preparations can be designed to alter functions associated with specific components of the microbiome. Because a marked increase in snack consumption is associated with westernization, we formulated snack prototypes using plant fibres from different sustainable sources that targeted distinct features of the gut microbiomes of individuals with obesity when transplanted into gnotobiotic mice. We used these snacks to supplement controlled diets that were consumed by adult individuals with obesity or who were overweight. Fibre-specific changes in their microbiomes were linked to changes in their plasma proteomes indicative of an altered physiological state.

Sensory and physical characteristics of foods that impact food intake without affecting acceptability: Systematic review and meta-analyses.

This systematic review with meta-analyses aimed to identify the sensory and physical characteristics of foods/beverages which increase satiation and/or decrease/delay subsequent consumption without affecting acceptability. Systematic searches were first undertaken to identify review articles investigating the effects of any sensory and physical food characteristic on food intake. These articles provided some evidence that various textural parameters (aeration, hardness, homogeneity, viscosity, physical form, added water) can impact food intake. Individual studies investigating these effects while also investigating acceptability were then assessed. Thirty-seven individual studies investigated a textural manipulation and provided results on food intake and acceptability, 13 studies (27 comparisons, 898 participants) investigated effects on satiation, and 29 studies (54 comparisons, 916 participants) investigated effects on subsequent intake. Meta-analyses of within-subjects comparisons (random-effects models) demonstrated greater satiation (less weight consumed) from food products that were harder, chunkier, more viscous, voluminous, and/or solid, while demonstrating no effects on acceptability. Textural parameters had limited effects on subsequent consumption. Between-subjects studies and sensitivity analyses confirmed these results. These findings provide some evidence that textural parameters can increase satiation without affecting acceptability. The development of harder, chunkier, more viscous, voluminous, and/or solid food/beverage products may be of value in reducing overconsumption.

Effects of alpha-glucosidase-inhibiting drugs on acute postprandial glucose and insulin responses: a systematic review and meta-analysis.

BACKGROUND/OBJECTIVES: Despite considerable literature supporting the potential health benefits of reducing postprandial glucose (PPG), and insulin (PPI) exposures, the size of a clinically relevant reduction is currently unknown. We performed a systematic review and meta-analysis to quantify effects of alpha-glucosidase-inhibiting (AGI) drugs on acute PPG and PPI responses. METHODS: We searched EMBASE and MEDLINE until March 13, 2018 for controlled studies using AGI drugs together with a standardized carbohydrate load or mixed meal. The mean incremental PPG and PPI levels were calculated as outcomes. Meta-analyses, stratified by diabetes state, were performed by using random effects models. RESULTS: The 66 included publications comprised 127 drug-control comparisons for PPG, and 106 for PPI, mostly testing acarbose or miglitol. The absolute effects on PPG were larger among individuals with diabetes (-1.5 mmol/l mean PPG [95% CI -1.9, -1.1] by acarbose, and -1.6 [-1.9, -1.4] by miglitol) as compared to individuals without diabetes (-0.4 [95% CI -0.5, -0.3] by acarbose, and -0.6 [-0.8, -0.4] by miglitol). Relative reductions in PPG by both drugs were similar for diabetic and non-diabetic individuals (43-54%). Acarbose and miglitol also significantly reduced mean PPI, with absolute and relative reductions being largest among individuals without diabetes. CONCLUSIONS: The present meta-analyses provide quantitative estimates of reductions of PPG and PPI responses by AGI drugs in diabetes and non-diabetic individuals. These data can serve as benchmarks for clinically relevant reductions in PPG and PPI via drug or diet and lifestyle interventions.

Deep Dive Into the Effects of Food Processing on Limiting Starch Digestibility and Lowering the Glycemic Response.

During processing of cereal-based food products, starch undergoes dramatic changes. The objective of this work was to evaluate the impact of food processing on the starch digestibility profile of cereal-based foods using advanced imaging techniques, and to determine the effect of preserving starch in its native, slowly digestible form on its in vivo metabolic fate. Four different food products using different processing technologies were evaluated: extruded products, rusks, soft-baked cakes, and rotary-molded biscuits. Imaging techniques (X-ray diffraction, micro-X-ray microtomography, and electronic microscopy) were used to investigate changes in slowly digestible starch (SDS) structure that occurred during these different food processing technologies. For in vivo evaluation, International Standards for glycemic index (GI) methodology were applied on 12 healthy subjects. Rotary molding preserved starch in its intact form and resulted in the highest SDS content (28 g/100 g) and a significantly lower glycemic and insulinemic response, while the three other technologies resulted in SDS contents below 3 g/100 g. These low SDS values were due to greater disruption of the starch structure, which translated to a shift from a crystalline structure to an amorphous one. Modulation of postprandial glycemia, through starch digestibility modulation, is a meaningful target for the prevention of metabolic diseases.

Reducing postprandial glucose in dietary intervention studies and the magnitude of the effect on diabetes-related risk factors: a systematic review and meta-analysis.

PURPOSE: Reducing postprandial hyperglycemia has beneficial effects on diabetes-related risk factors, but the magnitude of the reduction needed to achieve such an effect is unknown. The purpose of the study was to quantify the relationship of acute glucose and insulin postprandial responses with longer-term effects on diabetes-related risk factors by performing a systematic review and meta-analysis of dietary intervention studies. METHODS: We systematically searched EMBASE and MEDLINE. Dietary intervention studies among any human population aiming to reduce postprandial glycemia, with actual measures of postprandial glucose (PPG) and/or insulin (PPI) as acute exposures (incremental area under the curve, iAUC) as well as markers of glucose metabolism (fasting glucose, HbA1c) and insulin sensitivity (fasting insulin, HOMA-IR) after at least 4 weeks of diet intervention as outcomes were included. Meta-analyses were performed for the effects on acute exposures and on diabetes-related risk factors. The relationship between changes in acute exposures and changes in risk factor outcomes was estimated by meta-regression analyses. RESULTS: Out of the 13,004 screened papers, 13 papers with 14 comparisons were included in the quantitative analysis. The dietary interventions acutely reduced mean PPG [mean difference (MD), - 0.27 mmol/l; 95% CI - 0.41 to - 0.14], but not mean PPI (MD - 7.47 pmol/l; 95% CI - 16.79 to 1.86). There were no significant overall effects on fasting glucose and insulin. HbA1c was reduced by - 0.20% (95% CI - 0.35 to - 0.05). Changes in acute PPG were significantly associated with changes in fasting plasma glucose (FPG) [per 10% change in PPG: ß = 0.085 (95% CI 0.003, 0.167), k = 14], but not with fasting insulin [ß = 1.20 (95% CI - 0.32, 2.71), k = 12]. Changes in acute PPI were not associated with changes in FPG [per 10% change in PPI: ß = - 0.017 (95% CI - 0.056, 0.022), k = 11]. CONCLUSIONS: Only a limited number of postprandial glucose-lowering dietary intervention studies measured acute postprandial exposures to PPG/PPI during the interventions. In this small heterogeneous set of studies, an association was found between the magnitude of the acute postprandial responses and the change in fasting glucose, but no other outcomes. More studies are needed to quantify the relationship between acute postprandial changes and long-term effects on risk factors.

Starch digestibility modulation significantly improves glycemic variability in type 2 diabetic subjects: A pilot study.

BACKGROUND AND AIMS: In type 2 diabetes (T2D) patients, the reduction of glycemic variability and postprandial glucose excursions is essential to limit diabetes complications, beyond HbA1c level. This study aimed at determining whether increasing the content of Slowly Digestible Starch (SDS) in T2D patients' diet could reduce postprandial hyperglycemia and glycemic variability compared with a conventional low-SDS diet. METHODS AND RESULTS: For this randomized cross-over pilot study, 8 subjects with T2D consumed a controlled diet for one week, containing starchy products high or low in SDS. Glycemic variability parameters were evaluated using a Continuous Glucose Monitoring System. Glycemic variability was significantly lower during High-SDS diet compared to Low-SDS diet for MAGE (Mean Amplitude of Glycemic Excursions, p < 0.01), SD (Standard Deviation, p < 0.05), and CV (Coefficient of Variation, p < 0.01). The TIR (Time In Range) [140-180 mg/dL[ was significantly higher during High-SDS diet (p < 0.0001) whereas TIRs ≥180 mg/dL were significantly lower during High-SDS diet. Post-meals tAUC (total Area Under the Curve) were significantly lower during High-SDS diet. CONCLUSION: One week of High-SDS Diet in T2D patients significantly improves glycemic variability and reduces postprandial glycemic excursions. Modulation of starch digestibility in the diet could be used as a simple nutritional tool in T2D patients to improve daily glycemic control. REGISTRATION NUMBER: in clinicaltrials.gov: NCT03289494.

Development of a Repertoire and a Food Frequency Questionnaire for Estimating Dietary Fiber Intake Considering Prebiotics: Input from the FiberTAG Project.

Most official food composition tables and food questionnaires do not provide enough data to assess fermentable dietary fibers (DF) that can exert a health effect through their interaction with the gut microbiota. The aim of this study was to develop a database and a food frequency questionnaire (FFQ) allowing detailed DF intake estimation including prebiotic (oligo)saccharides. A repertoire of DF detailing total, soluble DF, insoluble DF and prebiotic (oligo)saccharides (inulin-type fructans, fructo-oligosaccharides and galacto-oligosaccharides) in food products consumed in Europe has been established. A 12 month FFQ was developed and submitted to 15 healthy volunteers from the FiberTAG study. Our data report a total DF intake of 38 g/day in the tested population. Fructan and fructo-oligosaccharides intake, linked notably to condiments (garlic and onions) ingestion, reached 5 and 2 g/day, respectively, galacto-oligosaccharides intake level being lower (1 g/day). We conclude that the FiberTAG repertoire and FFQ are major tools for the evaluation of the total amount of DF including prebiotics. Their use can be helpful in intervention or observational studies devoted to analyze microbiota-nutrient interactions in different pathological contexts, as well as to revisit DF intake recommendations as part of healthy lifestyles considering specific DF.

Design and Validation of a Diet Rich in Slowly Digestible Starch for Type 2 Diabetic Patients for Significant Improvement in Glycemic Profile.

This study aimed at designing a-diet high in slowly digestible starch (SDS) by carefully selecting high-SDS starchy products and to validate its implementation, acceptance, and impact on the postprandial glycemic response in patients with type 2 diabetes (T2D). Starchy products were screened and classified as being either high (high-SDS) or low (low-SDS) in SDS (in vitro SDS method). A randomized controlled cross-over pilot study was performed: Eight patients with T2D consumed randomly a high-SDS or a low-SDS diet for one week each, while their glycemic profile was monitored for 6 days. Based on 250 food product SDS analyses and dietary recommendations for patients with T2D, the high-SDS and low-SDS diets were designed. The high-SDS diet significantly increased SDS intake and the SDS/carbohydrates proportion compared to the low-SDS diet (61.6 vs. 11.6 g/day and 30% vs. 6%; p < 0.0001, respectively). Increasing the SDS/carbohydrate proportion to 50% of the meal was significantly correlated with a 12% decrease in tAUC0-120 min and a 14% decrease in the glycemic peak value (p < 0.001 for both). A high-SDS diet can be easily designed by carefully selecting commercial starchy products and providing relevant recommendations for T2D to improve their glycemic profile.

Potential Markers of Dietary Glycemic Exposures for Sustained Dietary Interventions in Populations without Diabetes.

There is considerable interest in dietary and other approaches to maintaining blood glucose concentrations within the normal range and minimizing exposure to postprandial hyperglycemic excursions. The accepted marker to evaluate the sustained maintenance of normal blood glucose concentrations is glycated hemoglobin A1c (HbA1c). However, although this is used in clinical practice to monitor glycemic control in patients with diabetes, it has a number of drawbacks as a marker of efficacy of dietary interventions that might beneficially affect glycemic control in people without diabetes. Other markers that reflect shorter-term glycemic exposures have been studied and proposed, but consensus on the use and relevance of these markers is lacking. We have carried out a systematic search for studies that have tested the responsiveness of 6 possible alternatives to HbA1c as markers of sustained variation in glycemic exposures and thus their potential applicability for use in dietary intervention trials in subjects without diabetes: 1,5-anhydroglucitol (1,5-AG), dicarbonyl stress, fructosamine, glycated albumin (GA), advanced glycated end products (AGEs), and metabolomic profiles. The results suggest that GA may be the most promising for this purpose, but values may be confounded by effects of fat mass. 1,5-AG and fructosamine are probably not sensitive enough to the range of variation in glycemic exposures observed in healthy individuals. Use of measures based on dicarbonyls, AGEs, or metabolomic profiles would require further research into possible specific molecular species of interest. At present, none of the markers considered here is sufficiently validated and sensitive for routine use in substantiating the effects of sustained variation in dietary glycemic exposures in people without diabetes.

Interspecies Competition Impacts Targeted Manipulation of Human Gut Bacteria by Fiber-Derived Glycans.

Development of microbiota-directed foods (MDFs) that selectively increase the abundance of beneficial human gut microbes, and their expressed functions, requires knowledge of both the bioactive components of MDFs and the mechanisms underlying microbe-microbe interactions. Here, gnotobiotic mice were colonized with a defined consortium of human-gut-derived bacterial strains and fed different combinations of 34 food-grade fibers added to a representative low-fiber diet consumed in the United States. Bioactive carbohydrates in fiber preparations targeting particular Bacteroides species were identified using community-wide quantitative proteomic analyses of bacterial gene expression coupled with forward genetic screens. Deliberate manipulation of community membership combined with administration of retrievable artificial food particles, consisting of paramagnetic microscopic beads coated with dietary polysaccharides, disclosed the contributions of targeted species to fiber degradation. Our approach, including the use of bead-based biosensors, defines nutrient-harvesting strategies that underlie, as well as alleviate, competition between Bacteroides and control the selectivity of MDF components.