Vinegar as a functional ingredient to improve postprandial glycemic control-human intervention findings and molecular mechanisms

Fermented foods and gastrointestinal health: underlying mechanisms

Although fermentation probably originally developed as a means of preserving food substrates, many fermented foods (FFs), and components therein, are thought to have a beneficial effect on various aspects of human health, and gastrointestinal health in particular. It is important that any such perceived benefits are underpinned by rigorous scientific research to understand the associated mechanisms of action. Here, we review in vitro, ex vivo and in vivo studies that have provided insights into the ways in which the specific food components, including FF microorganisms and a variety of bioactives, can contribute to health-promoting activities. More specifically, we draw on representative examples of FFs to discuss the mechanisms through which functional components are produced or enriched during fermentation (such as bioactive peptides and exopolysaccharides), potentially toxic or harmful compounds (such as phytic acid, mycotoxins and lactose) are removed from the food substrate, and how the introduction of fermentation-associated live or dead microorganisms, or components thereof, to the gut can convey health benefits. These studies, combined with a deeper understanding of the microbial composition of a wider variety of modern and traditional FFs, can facilitate the future optimization of FFs, and associated microorganisms, to retain and maximize beneficial effects in the gut.

RNA-seq Analysis Reveals Potential Synergic Effects of Acetate and Cold Exposure on Interscapular Brown Adipose Tissue in Mice

Brown adipose tissue (BAT) exhibits remarkable morphological and functional plasticity in response to environmental (e.g., cold exposure) and nutrient (e.g., high-fat diet) stimuli. Notably, a number of studies have showed that acetate, the main fermentation product of dietary fiber in gut, profoundly influences the differentiation and activity of BAT. However, the potential synergic or antagonistic effects of acetate and cold exposure on BAT have not been well examined. In the present study, the C57BL/6J mice were treated with acetate at the systemic level before a short period of cold exposure. Physiological parameters including body weight, blood glucose, and Respiratory Exchange Ratio (RER) were monitored, and thermal imaging of body surface temperature was captured. Moreover, the transcriptome profiles of interscapular BAT were also determined and analyzed afterwards. The obtained results showed that acetate treatment prior to cold exposure could alter the gene expression profile, as evidenced by significant differential clusters between the two groups. GO analysis and KEGG analysis further identified differentially expressed genes being mainly enriched for a number of biological terms and pathways related to lipid metabolism and brown adipose activity such as "G-protein-coupled receptor activity", "cAMP metabolic process", "PPAR signaling pathway", and "FoxO signaling pathway". GSEA analysis further suggested that activation status of key pathways including "PPAR signaling pathway" and "TCA cycle" were altered upon acetate treatment. Taken together, our study identified the potential synergistic effect of acetic acid with cold exposure on BAT, which highlighted the positive dietary and therapeutic aspects of acetate.

2'-fucosyllactose alone or combined with resistant starch increases circulating short-chain fatty acids in lean men and men with prediabetes and obesity

Background

Infusion of short-chain fatty acids (SCFA) to the distal colon beneficially affects human substrate and energy metabolism. Here, we hypothesized that the combination of 2'-fucosyllactose (2'-FL) with resistant starch (RS) increases distal colonic SCFA production and improves metabolic parameters.

Methods

In this randomized, crossover study, 10 lean (BMI 20-24.9 kg/m²) and nine men with prediabetes and overweight/obesity (BMI 25-35 kg/m²) were supplemented with either 2'-FL, 2'-FL+RS, or placebo one day before a clinical investigation day (CID). During the CID, blood samples were collected after a overnight fast and after intake of a liquid high-fat mixed meal to determine plasma SCFA (primary outcomes). Secondary outcomes were fasting and postprandial plasma insulin, glucose, free fatty acid (FFA), glucagon-like peptide-1, and peptide YY concentrations. In addition, fecal SCFA and microbiota composition, energy expenditure and substrate oxidation (indirect calorimetry), and breath hydrogen excretion were determined.

Results

In lean men, supplementation with 2'-FL increased postprandial plasma acetate (P = 0.017) and fasting H₂ excretion (P = 0.041) compared to placebo. Postprandial plasma butyrate concentration increased after 2'-FL and 2'-FL+RS as compared to placebo (P < 0.05) in lean men and men with prediabetes and overweight/obesity. Additionally, 2'-FL+RS decreased fasting and postprandial plasma FFA concentrations compared to placebo (P < 0.05) in lean men.

Conclusion

Supplementation of 2'-FL with/without RS the day before investigation increased systemic butyrate concentrations in lean men as well as in men with prediabetes and obesity, while acetate only increased in lean men. The combination of 2'-FL with RS showed a putatively beneficial metabolic effect by lowering plasma FFA in lean men, indicating a phenotype-specific effect.

Clinical trial registration

nr. NCT04795804.

Gut Microbial-Derived Short Chain Fatty Acids: Impact on Adipose Tissue Physiology

Obesity is a global public health issue and major risk factor for pathological conditions, including type 2 diabetes, dyslipidemia, coronary artery disease, hepatic steatosis, and certain types of cancer. These metabolic complications result from a combination of genetics and environmental influences, thus contributing to impact whole-body homeostasis. Mechanistic animal and human studies have indicated that an altered gut microbiota can mediate the development of obesity, leading to inflammation beyond the intestine. Moreover, prior research suggests an interaction between gut microbiota and peripheral organs such as adipose tissue via different signaling pathways; yet, to what degree and in exactly what ways this inter-organ crosstalk modulates obesity remains elusive. This review emphasizes the influence of circulating gut-derived short chain fatty acids (SCFAs) i.e., acetate, propionate, and butyrate, on adipose tissue metabolism in the scope of obesity, with an emphasis on adipocyte physiology in vitro and in vivo. Furthermore, we discuss some of the well-established mechanisms via which microbial SCFAs exert a role as a prominent host energy source, hence regulating overall energy balance and health. Collectively, exploring the mechanisms via which SCFAs impact adipose tissue metabolism appears to be a promising avenue to improve metabolic conditions related to obesity.

Fiber mixture-specific effect on distal colonic fermentation and metabolic health in lean but not in prediabetic men

Infusions of the short-chain fatty acid (SCFA) acetate in the distal colon improved metabolic parameters in men. Here, we hypothesized that combining rapidly and slowly fermentable fibers will enhance distal colonic acetate production and improve metabolic health. In vitro cultivation studies in a validated model of the colon were used to identify fiber mixtures that yielded high distal colonic acetate production. Subsequently, in two randomized crossover studies, lean and prediabetic overweight/obese men were included. In one study, participants received supplements of either long-chain inulin+resistant starch (INU+RS), INU or maltodextrin (PLA) the day prior to a clinical investigation day (CID). The second trial studied beta glucan+RS (BG+RS) versus BG and PLA. During each CID, breath hydrogen, indirect calorimetry, plasma metabolites/hormones were assessed during fasting and postprandial conditions. Additionally, fecal microbiota composition and SCFA were determined. In prediabetic men, INU+RS increased plasma acetate compared to INU or PLA (P < .05), but did not affect metabolic parameters. In lean men, INU+RS increased breath hydrogen and fasting plasma butyrate, which was accompanied by increased energy expenditure, carbohydrate oxidation and PYY and decreased postprandial glucose concentrations (all P < .05) compared to PLA. BG+RS increased plasma butyrate compared to PLA (P < .05) in prediabetic individuals, but did not affect other fermentation/metabolic markers in both phenotypes. Fiber-induced shifts in fecal microbiota were individual-specific and more pronounced with INU+RS versus BG+RS. Administration of INU+RS (not BG+RS) the day prior to investigation improved metabolic parameters in lean but not in prediabetic individuals, demonstrating that effects were phenotype- and fiber-specific. Further research should study whether longer-term supplementation periods are required to elicit beneficial metabolic health in prediabetic individuals. Trial registration numbers: Clinical trial No. NCT03711383 (Inulin study) and Clinical trial No. NCT03714646 (Beta glucan study).

Glycemic response, satiety, gastric secretions and emptying after bread consumption with water, tea or lemon juice: a randomized crossover intervention using MRI

PURPOSE

Numerous studies, including our previous work with lemon juice, have reported that low-pH meals reduce the glycemic response to starchy foods. However, the underlying mechanism is not yet understood. Tea, for its polyphenol content, has also been investigated. The main objective of this research was to concurrently study gastric emptying, appetite perceptions and glycemic responses to bread consumed with water, tea, or lemon juice.

METHODS

In this randomized, crossover intervention, ten participants consumed equal portions of bread (100 g) with 250 mL of water, water-diluted lemon juice, or black tea at breakfast. Gastric volumes, blood glucose concentrations and appetite perceptions were alternately assessed over 180 min using magnetic resonance imaging, the finger-prick method and visual analogue scales, respectively.

RESULTS

Compared to water, lemon juice led to a 1.5 fold increase of the volume of gastric contents, 30 min after the meal (454.0 ± 18.6 vs. 298.4 ± 19.5 mL, [Formula: see text]  ± SEM P < 0.00001). Gastric emptying was also 1.5 times faster (P < 0.01). Conversely, lemon juice elicited a lower glycemic response than water (blood glucose concentrations at t = 55 min were 35% lower, P = 0.039). Tea had no effect. Changes in appetite perceptions and gastric volumes correlated well, but with no significant differences between the meals.

CONCLUSIONS

Lemon juice lowered the glycemic response and increased both gastric secretions and emptying rate. The results are compatible with the hypothesis that the reduction of the glycemic response is mainly due to the interruption of starch hydrolysis via the acid-inhibition of salivary α-amylase.

TRIAL REGISTRATION NUMBER

NCT03265392, August 29, 2017.

Desulfovibrio vulgaris, a potent acetic acid-producing bacterium, attenuates nonalcoholic fatty liver disease in mice

The emerging evidence supports the use of prebiotics like herb-derived polysaccharides for treating nonalcoholic fatty liver disease (NAFLD) by modulating gut microbiome. The present study was initiated on the microbiota-dependent anti-NAFLD effect of Astragalus polysaccharides (APS) extracted from Astragalus mongholicus Bunge in high-fat diet (HFD)-fed mice. However, the exact mechanisms underlying the beneficial effects of APS on NAFLD formation remain poorly understood.Co-housing experiment was used to assess the microbiota dependent anti-NAFLD effect of APS. Then, targeted metabolomics and metagenomics were adopted for determining short-chain fatty acids (SCFAs) and bacteria that were specifically enriched by APS. Further in vitro experiment was carried out to test the capacity of SCFAs-producing of identified bacterium. Finally, the anti-NAFLD efficacy of identified bacterium was tested in HFD-fed mice.Our results first demonstrated the anti-NAFLD effect of APS in HFD-fed mice and the contribution of gut microbiota. Moreover, our results indicated that SCFAs, predominantly acetic acid were elevated in APS-supplemented mice and ex vivo experiment. Metagenomics revealed that D. vulgaris from Desulfovibrio genus was not only enriched by APS, but also a potent generator of acetic acid, which showed significant anti-NAFLD effects in HFD-fed mice. In addition, D. vulgaris modulated the hepatic gene expression pattern of lipids metabolism, particularly suppressed hepatic fatty acid synthase (FASN) and CD36 protein expression.Our results demonstrate that APS enriched D. vulgaris is effective on attenuating hepatic steatosis possibly through producing acetic acid, and modulation on hepatic lipids metabolism in mice. Further studies are warranted to explore the long-term impacts of D. vulgaris on host metabolism and the underlying mechanism.

Repression of HDAC5 by acetate restores hypothalamic-pituitary-ovarian function in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) accounts for 90-95 % of worldwide diabetes cases and is primarily characterized by insulin resistance. Its progression as a chronic metabolic disease has been largely associated with female reproductive abnormalities, including ovarian dysfunction with consequent infertility. Epigenetic modifications have been suggested as a possible link to metabolic comorbidities. We therefore hypothesized that short chain fatty acids, acetate (ACA), a potential histone deacetylase inhibitor (HDAC) ameliorates hypothalamic-pituitary-ovarian (HPO) dysfunction in T2DM. Female Wistar rats weighing 160-190 g were allotted into three groups (n = 6/group): Control (vehicle; po), T2D and T2D + ACA (200 mg/kg; po). T2DM was induced by fructose administration (10 %; w/v) for 6 weeks and single dose of streptozotocin (35 mg/kg; ip). The present data showed that in addition to insulin resistance, increased fasting blood glucose and insulin, T2DM induced elevated plasma, hypothalamic and ovarian triglyceride, lipid peroxidation, TNF-α and glutathione depletion. Aside, T2DM also led to increased plasma lactate production and γ-Glutamyl transferase as well as decreased gonadotropins/17β-estradiol. Histologically, hypothalamus, pituitary and ovaries revealed disrupted neuronal cells/moderate hemorrhage, altered morphology/vascular congestions, and degenerated antral follicle/graafian follicle with mild fibrosis and infiltrated inflammatory cells respectively in T2D animals. Interestingly, these alterations were accompanied by elevated plasma/hypothalamic HDAC5 and attenuated when treated with acetate. The present results demonstrate that T2DM induces HPO dysfunction, which is accompanied by elevated circulating/hypothalamic HDAC5. The results in addition suggest that acetate restores HPO function in T2DM by suppression of HDAC5 and enhancement of insulin sensitivity.

Childhood overeating is associated with adverse cardiometabolic and inflammatory profiles in adolescence

Childhood eating behaviour contributes to the rise of obesity and related noncommunicable disease worldwide. However, we lack a deep understanding of biochemical alterations that can arise from aberrant eating behaviour. In this study, we prospectively associate longitudinal trajectories of childhood overeating, undereating, and fussy eating with metabolic markers at age 16 years to explore adolescent metabolic alterations related to specific eating patterns in the first 10 years of life. Data are from the Avon Longitudinal Study of Parents and Children (n = 3104). We measure 158 metabolic markers with a high-throughput (1H) NMR metabolomics platform. Increasing childhood overeating is prospectively associated with an adverse cardiometabolic profile (i.e., hyperlipidemia, hypercholesterolemia, hyperlipoproteinemia) in adolescence; whereas undereating and fussy eating are associated with lower concentrations of the amino acids glutamine and valine, suggesting a potential lack of micronutrients. Here, we show associations between early behavioural indicators of eating and metabolic markers.

Faecal microbial metabolites of proteolytic and saccharolytic fermentation in relation to degree of insulin resistance in adult individuals

The gut microbiota may affect host metabolic health through microbial metabolites. The balance between the production of microbial metabolites by saccharolytic and proteolytic fermentation may be an important determinant of metabolic health. Amongst the best-studied saccharolytic microbial metabolites are the short-chain fatty acids acetate, propionate and butyrate. However, human data on the role of other microbial fermentation by-products in metabolic health are greatly lacking. Therefore, we compared in a cross-sectional study the faecal microbial metabolites (caproate, lactate, valerate, succinate, and the branched-chain fatty acids (BCFA) (isobutyrate, isovalerate)) between insulin sensitive (homeostatic model assessment of insulin resistance (HOMA-IR), HOMA-IR<1.85, IS) and insulin resistant (HOMA-IR>1.85, IR) individuals. Additionally, we assessed the relationships between faecal metabolites and markers of metabolic health including fasting glucose, insulin, free fatty acids, insulin resistance (HOMA-IR) and fasting substrate oxidation in 86 individuals with a wide range of body mass index. Faecal metabolite concentrations did not significantly differ between IS and IR. Furthermore, there were no associations between microbial metabolites and metabolic health markers, except for a slight positive association of isovalerate with carbohydrate oxidation (E%, std β 0.194, P=0.011) and fat oxidation (E%, std β -0.075, P=0.047), also after adjustment for age, sex and BMI. In summary, faecal caproate, lactate, valerate, succinate, and BCFA (isobutyrate, isovalerate) were not different between IR and IS individuals, nor was there any association between these faecal metabolites and parameters of metabolic health. Further human intervention studies are warranted to investigate the role of these microbially-derived fermentation products and their kinetics in metabolic health and insulin sensitivity.

Health Promoting Properties of Cereal Vinegars

Vinegar has been used for its health promoting properties since antiquity. Nowadays, these properties are investigated, scientifically documented, and highlighted. The health benefits of vinegar have been associated with the presence of a variety of bioactive components such as acetic acid and other organic acids, phenolic compounds, amino acids, carotenoids, phytosterols, vitamins, minerals, and alkaloids, etc. These components are known to induce responses in the human body, such as antioxidant, antidiabetic, antimicrobial, antitumor, antiobesity, antihypertensive, and anti-inflammatory effects. The diversity and levels of bioactive components in vinegars depend on the raw material and the production method used. Cereal vinegars, which are more common in the Asia-Pacific region, are usually made from rice, although other cereals, such as millet, sorghum, barley, malt, wheat, corn, rye, oats, bran and chaff, are also used. A variety of bioactive components, such as organic acids, polyphenols, amino acids, vitamins, minerals, alkaloids, melanoidins, butenolides, and specific compounds such as γ-oryzanol, tetramethylpyrazine, γ-aminobutyric acid, etc., have been associated with the health properties of cereal vinegars. In this work, the bioactive components and the related health effects of cereal vinegars are reviewed, and the most recent scientific literature is presented and discussed.

Effect of Dietary Acetic Acid Supplementation on Plasma Glucose, Lipid Profiles, and Body Mass Index in Human Adults: A Systematic Review and Meta-analysis

BACKGROUND

Acetic acid is a short-chain fatty acid that has demonstrated biomedical potential as a dietary therapeutic agent for the management of chronic and metabolic illness comorbidities. In human beings, its consumption may improve glucose regulation and insulin sensitivity in individuals with cardiometabolic conditions and type 2 diabetes mellitus. Published clinical trial evidence evaluating its sustained supplementation effects on metabolic outcomes is inconsistent.

OBJECTIVE

This systematic review and meta-analysis summarized available evidence on potential therapeutic effects of dietary acetic acid supplementation via consumption of acetic acid-rich beverages and food sources on metabolic and anthropometric outcomes.

METHODS

A systematic search was conducted in Medline, Scopus, EMBASE, CINAHL Plus, and Web of Science from database inception until October 2020. Randomized controlled trials conducted in adults evaluating the effect of dietary acetic acid supplementation for a minimum of 1 week were included. Meta-analyses were performed using a random-effects model on fasting blood glucose (FBG), triacylglycerol (TAG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), glycated hemoglobin (HbA1c), body mass index (BMI), and body fat percentage. Statistical heterogeneity was assessed by calculation of Q and I² statistics, and publication bias was assessed by calculation of Egger's regression asymmetry and Begg's test.

RESULTS

Sixteen studies were included, involving 910 participants who consumed between 750 and 3600 mg acetic acid daily in interventions lasting an average of 8 weeks. Dietary acetic acid supplementation resulted in significant reductions in TAG concentrations in overweight and obese but otherwise healthy individuals (mean difference [MD] = -20.51 mg/dL [95% confidence intervals = -32.98, -8.04], P = .001) and people with type 2 diabetes (MD = -7.37 mg/dL [-10.15, -4.59], P < .001). Additionally, acetic acid supplementation significantly reduced FBG levels (MD = -35.73 mg/dL [-63.79, -7.67], P = .01) in subjects with type 2 diabetes compared with placebo and low-dose comparators. No other changes were seen for other metabolic or anthropometric outcomes assessed. Five of the 16 studies did not specify the dose of acetic acid delivered, and no studies measured blood acetate concentrations. Only one study controlled for background acetic acid-rich food consumption during intervention periods. Most studies had an unclear or high risk of bias.

CONCLUSION

Supplementation with dietary acetic acid is well tolerated, has no adverse side effects, and has clinical potential to reduce plasma TAG and FBG concentrations in individuals with type 2 diabetes, and to reduce TAG levels in people who are overweight or obese. No significant effects of dietary acetic acid consumption were seen on HbA1c, HDL, or anthropometric markers. High-quality, longer-term studies in larger cohorts are required to confirm whether dietary acetic acid can act as an adjuvant therapeutic agent in metabolic comorbidities management.

Acetate Revisited: A Key Biomolecule at the Nexus of Metabolism, Epigenetics, and Oncogenesis - Part 2: Acetate and ACSS2 in Health and Disease

Acetate, the shortest chain fatty acid, has been implicated in providing health benefits whether it is derived from the diet or is generated from microbial fermentation of fiber in the gut. These health benefits range widely from improved cardiac function to enhanced red blood cell generation and memory formation. Understanding how acetate could influence so many disparate biological functions is now an area of intensive research. Protein acetylation is one of the most common post-translational modifications and increased systemic acetate strongly drives protein acetylation. By virtue of acetylation impacting the activity of virtually every class of protein, acetate driven alterations in signaling and gene transcription have been associated with several common human diseases, including cancer. In part 2 of this review, we will focus on some of the roles that acetate plays in health and human disease. The acetate-activating enzyme acyl-CoA short-chain synthetase family member 2 (ACSS2) will be a major part of that focus due to its role in targeted protein acetylation reactions that can regulate central metabolism and stress responses. ACSS2 is the only known enzyme that can recycle acetate derived from deacetylation reactions in the cytoplasm and nucleus of cells, including both protein and metabolite deacetylation reactions. As such, ACSS2 can recycle acetate derived from histone deacetylase reactions as well as protein deacetylation reactions mediated by sirtuins, among many others. Notably, ACSS2 can activate acetate released from acetylated metabolites including N-acetylaspartate (NAA), the most concentrated acetylated metabolite in the human brain. NAA has been associated with the metabolic reprograming of cancer cells, where ACSS2 also plays a role. Here, we discuss the context-specific roles that acetate can play in health and disease.

Sodium acetate-mediated inhibition of histone deacetylase alleviates hepatic lipid dysregulation and its accompanied injury in streptozotocin-nicotinamide-induced diabetic rats

OBJECTIVE

Hepatic lipid dysregulation with consequent lipotoxicity remains critical in the progression of non-alcoholic fatty liver disease, a rising prevalent complication of diabetes mellitus particularly type 2 diabetes. Diabetes-associated hepatic complications are among the leading causes of liver-related morbidity and mortality worldwide. Short chain fatty acids (SCFAs) have been demonstrated to regulate glycemic metabolism but its effect on diabetes-driven hepatic perturbation is unknown. This study is therefore designed to investigate the effect of SCFAs, acetate on diabetes-characterised hepatic lipotoxicity, and plausible involvement of histone deacetylase (HDAC) activity.

METHODS

Adult male Wistar rats (230-260 g) were allotted into groups (n = 6/group) namely: control (vehicle; p.o.), sodium acetate (SAT)-treated (200 mg/kg), diabetic with/without SAT groups. Diabetes was induced by intraperitoneal injection of streptozotocin 65 mg/kg after a dose of nicotinamide 110 mg/kg.

RESULTS

Data from diabetic animals showed increased fasting glycemia and insulinemia, decreased insulin sensitivity and body weight with increased relative hepatic mass. It also revealed increased hepatic lipid, serum/hepatic malondialdehyde, tissue necrosis factor-α, uric acid, aspartate transaminase, alanine aminotransferase and decreased glutathione content with elevated hepatic HDAC. Histologically, the hepatic tissue was characterised with disrupted architecture, inflammation of central vein and foci of periportal and sinusoidal cellular infiltration. However, these alterations were attenuated by sodium acetate.

CONCLUSION

The study demonstrates that diabetes mellitus drives hepatic lipotoxicity, characterised with lipid accumulation, excessive lipid peroxidation, pro-inflammation, depleted glutathione content and accompanied by increased HDAC activity. Besides, the study suggests that acetate ameliorates diabetes-associated hepatic lipotoxicity through HDAC suppression and enhancement of insulin sensitivity.

Lemon juice, but not tea, reduces the glycemic response to bread in healthy volunteers: a randomized crossover trial

PURPOSE

The inhibition of enzymes that hydrolyze starch during digestion could constitute an opportunity to slow down the release, and ultimately the uptake, of starch-derived glucose. Simple dietary approaches consisting in pairing starch-rich foods with beverages that have the capacity to inhibit such enzymes could be an effective and easily implementable strategy. The objective of this work was to test the impact of black tea and lemon juice on the glycemic response to bread and subsequent energy intake in healthy adults.

METHODS

A randomized crossover study was conducted with equal portions of bread (100 g) and 250 ml of water, black tea or lemon juice. Capillary blood glucose concentrations were monitored during 180 min using the finger-prick method. Ad libitum energy intake was assessed 3 h later.

RESULTS

Tea had no effect on the glycemic response. Lemon juice significantly lowered the mean blood glucose concentration peak by 30% (p < 0.01) and delayed it more than 35 min (78 vs. 41 min with water, p < 0.0001). None of the tested beverages had an effect on ad libitum energy intake.

CONCLUSION

These results are in agreement with previous in vitro studies showing that lowering the pH of a meal can slow down starch digestion through premature inhibition of salivary α-amylase. Furthermore, the effect of lemon juice was similar to what has been repeatedly observed with vinegar and other acidic foods. Including acidic beverages or foods in starchy meals thus appears to be a simple and effective strategy to reduce their glycemic impact.

The Short-Chain Fatty Acid Acetate in Body Weight Control and Insulin Sensitivity

The interplay of gut microbiota, host metabolism, and metabolic health has gained increased attention. Gut microbiota may play a regulatory role in gastrointestinal health, substrate metabolism, and peripheral tissues including adipose tissue, skeletal muscle, liver, and pancreas via its metabolites short-chain fatty acids (SCFA). Animal and human data demonstrated that, in particular, acetate beneficially affects host energy and substrate metabolism via secretion of the gut hormones like glucagon-like peptide-1 and peptide YY, which, thereby, affects appetite, via a reduction in whole-body lipolysis, systemic pro-inflammatory cytokine levels, and via an increase in energy expenditure and fat oxidation. Thus, potential therapies to increase gut microbial fermentation and acetate production have been under vigorous scientific scrutiny. In this review, the relevance of the colonically and systemically most abundant SCFA acetate and its effects on the previously mentioned tissues will be discussed in relation to body weight control and glucose homeostasis. We discuss in detail the differential effects of oral acetate administration (vinegar intake), colonic acetate infusions, acetogenic fiber, and acetogenic probiotic administrations as approaches to combat obesity and comorbidities. Notably, human data are scarce, which highlights the necessity for further human research to investigate acetate’s role in host physiology, metabolic, and cardiovascular health.

Relationship between diet/exercise and pharmacotherapy to enhance the GLP-1 levels in type 2 diabetes

The rapid rise in the prevalence of type 2 diabetes mellitus (T2DM) poses a huge healthcare burden across the world. Although there are several antihyperglycaemic agents (AHAs) available including addition of new drug classes to the treatment algorithm, more than 50% of patients with T2DM do not achieve glycaemic targets, suggesting an urgent need for treatment strategies focusing on prevention and progression of T2DM and its long-term complications. Lifestyle changes including implementation of healthy diet and physical activity are cornerstones for the management of T2DM. The positive effects of diet and exercise on incretin hormones such as glucagon-like peptide-1 (GLP-1) have been reported. We hypothesize an IDEP concept (Interaction between Diet/Exercise and Pharmacotherapy) aimed at modifying the diet and lifestyle, along with pharmacotherapy to enhance the GLP-1 levels, would result in good glycaemic control in patients with T2DM. Consuming protein-rich food, avoiding saturated fatty acids and making small changes in eating habits such as eating slowly with longer mastication time can have a positive impact on the GLP-1 secretion and insulin levels. Further the type of physical activity (aerobic/resistance training), intensity of exercise, duration, time and frequency of exercise have shown to improve GLP-1 levels. Apart from AHAs, a few antihypertensive drugs and lipid-lowering drugs have also shown to increase endogenous GLP-1 levels, however, due to quick degradation of GLP-1 by dipeptidyl peptidase-4 (DPP-4) enzyme, treatment with DPP-4 inhibitors would protect GLP-1 from degradation and prolong its activity. Thus, IDEP concept can be a promising treatment strategy, which positively influences the GLP-1 levels and provide additive benefits in terms of improving metabolic parameters in patients with T2DM and slowing the progression of T2DM and its associated complications.

Sex, gut microbiome, and cardiovascular disease risk

Key differences exist between men and women in the determinants and manifestations of cardiovascular and cardiometabolic diseases. Recently, gut microbiome-host relations have been implicated in cardiovascular disease and associated metabolic conditions; therefore, gut microbiota may be key mediators or modulators driving the observed sexual dimorphism in disease onset and progression. While current evidence regarding pure physiological sex differences in gut microbiome composition is modest, robust research suggests that gut microbiome-dependent metabolites may interact with important biological pathways under sex hormone control, including toll-like receptor and flavin monooxygenase signaling. Here, we review key sex differences in gut microbiome interactions with four primary determinants of cardiovascular disease, impaired glucose regulation, dyslipidemia, hypertension, and obesity. Through this process, we propose important sex differences in downstream metabolic pathways that may be at the interface of the gut microbiome and cardiovascular disease.

Acid induced reduction of the glycaemic response to starch-rich foods: the salivary α-amylase inhibition hypothesis

Numerous studies have reported that the glycaemic response to starch-rich meals can be reduced by 20-50% with acidic drinks or foods. A number of candidate explanations have been put forward, but this phenomenon still remains vaguely understood. This study intends to demonstrate the remarkable effect of acid inhibition of salivary α-amylase during oro-gastric hydrolysis of starch, shedding light on this often overlooked mechanism. Oro-gastric digestions of bread, wheat and gluten-free pastas, combined with either water or lemon juice were performed using a dynamic in vitro system that reproduces gastric acidification kinetics observed in humans. In the presence of water, large proportions of starch (25-85%) and oligosaccharides (15-50%) were released from all foods within the first hour of gastric digestion (pH > 3.5). In the presence of lemon juice (pH < 3.5 at all time), starch release was about twice as low, and amylolysis into oligosaccharides was completely interrupted. Acid-inhibition of salivary α-amylase may explain, at least in part, the reduction of the blood glucose response through acidification of starch-rich foods/meals. This offers new perspectives for the development of strategies to improve the glycaemic response elicited by starch-rich diets.

Diabetes Control: Is Vinegar a Promising Candidate to Help Achieve Targets?

BACKGROUND

Renewed interest in vinegar as a glucose-lowering agent led to several small trials in the recent past. However, none of the trials could independently provide sufficient evidence.

OBJECTIVES

Our review aimed to obtain reliable estimates of effects of vinegar on short-term and long-term blood glucose control.

METHODS

Large bibliographic databases were searched from inception to date of search without language and publication date restrictions. All clinical trials evaluating effect of vinegar on diabetes mellitus patients were eligible. Two authors independently extracted data on fasting and 2-hour postprandial blood glucose, insulin, and HbA1c levels at the various time points. MS Excel, SAS® v9.3, and RevMan v5.3 were used for data analysis.

RESULTS

Small significant reduction in mean HbA1c was observed after 8 to 12 weeks of vinegar administration: -0.39% (95% confidence interval = -0.59, -0.18; I² = 0%). Other long-term outcomes favored vinegar but were not significant. Short-term outcomes showed significantly lower pooled mean difference in glucose levels at 30 minutes in the vinegar group. Readings at 60, 90, and 120 minutes were lower in the vinegar group but not statistically significant. Adverse effects profile also favored the vinegar group.

CONCLUSIONS

It is worthwhile to carry out carefully planned large trails to determine the efficacy and effectiveness of vinegar as an adjunct treatment modality.

Acetate: a diet-derived key metabolite in energy metabolism: good or bad in context of obesity and glucose homeostasis?

PURPOSE OF REVIEW

To highlight recent research findings on effects of the short-chain fatty acid acetate in the control of body weight, insulin sensitivity, and glucose homeostasis. For this purpose, relevant animal and human in-vivo studies were reviewed and putative mechanisms and pathways were discussed.

RECENT FINDINGS

Animal and human in-vivo studies provide strong indications for a beneficial role of orally ingested or colonically derived acetate, in the energy and substrate metabolism, thereby preventing or reversing the obese insulin-resistant phenotype. However, data from rodents are conflicting and indicate that an increased acetate turnover promotes body weight gain and insulin resistance. A reason for these controversies may be related to the mode and site of acetate administration, as well as to the species and the metabolic phenotype of animals used.

SUMMARY

Overall, animal and human data suggest a direct regulatory role of acetate in several pathways involved in energy expenditure and fat utilization. In addition, acetate stimulates the release of gut-derived satiety-stimulating hormones and might regulate the inflammatory state. However, human intervention studies are required to evaluate the recent 'acetate discrepancies' and to confirm whether an increase in the acetate availability is a promising approach for the prevention and management of obesity and associated impairments in glucose and insulin metabolism.

Extraoral Taste Receptor Discovery: New Light on Ayurvedic Pharmacology

More and more research studies are revealing unexpectedly important roles of taste for health and pathogenesis of various diseases. Only recently it has been shown that taste receptors have many extraoral locations (e.g., stomach, intestines, liver, pancreas, respiratory system, heart, brain, kidney, urinary bladder, pancreas, adipose tissue, testis, and ovary), being part of a large diffuse chemosensory system. The functional implications of these taste receptors widely dispersed in various organs or tissues shed a new light on several concepts used in ayurvedic pharmacology (dravyaguna vijnana), such as taste (rasa), postdigestive effect (vipaka), qualities (guna), and energetic nature (virya). This review summarizes the significance of extraoral taste receptors and transient receptor potential (TRP) channels for ayurvedic pharmacology, as well as the biological activities of various types of phytochemical tastants from an ayurvedic perspective. The relative importance of taste (rasa), postdigestive effect (vipaka), and energetic nature (virya) as ethnopharmacological descriptors within Ayurveda boundaries will also be discussed.

Short-Chain Fatty Acids Differentially Affect Intracellular Lipolysis in a Human White Adipocyte Model

BACKGROUND AND AIMS

Gut-derived short-chain fatty acids (SCFA), formed by microbial fermentation of dietary fibers, are believed to be involved in the etiology of obesity and diabetes. Previous data from our group showed that colonic infusions of physiologically relevant SCFA mixtures attenuated whole-body lipolysis in overweight men. To further study potential mechanisms involved in the antilipolytic properties of SCFA, we aimed to investigate the in vitro effects of SCFA incubations on intracellular lipolysis and signaling using a human white adipocyte model, the human multipotent adipose tissue-derived stem (hMADS) cells.

METHODS

hMADS adipocytes were incubated with mixtures of acetate, propionate, and butyrate or single SCFA (acetate, propionate and butyrate) in concentrations ranging between 1 µmol/L and 1 mmol/L. Glycerol release and lipase activation was investigated during basal conditions and following β-adrenergic stimulation.

RESULTS

SCFA mixtures high in acetate and propionate decreased basal glycerol release, when compared to control (P < 0.05), while mixtures high in butyrate had no effect. Also, β-adrenergic receptor mediated glycerol release was not significantly altered following incubation with SCFA mixtures. Incubation with only acetate decreased basal (1 µmol/L) and β-adrenergically (1 µmol/L and 1 mmol/L) mediated glycerol release when compared with control (P < 0.05). In contrast, butyrate (1 µmol/L) slightly increased basal and β-adrenergically mediated glycerol release compared with control (P < 0.05), while propionate had no effect on lipolysis. The antilipolytic effect of acetate was accompanied by a reduced phosphorylation of hormone-sensitive lipase (HSL) at serine residue 650. In addition, inhibition of Gi G proteins following pertussis toxin treatment prevented the antilipolytic effect of acetate.

CONCLUSION

The present data demonstrated that acetate was mainly responsible for the antilipolytic effects of SCFA and acts via attenuation of HSL phosphorylation in a Gi-coupled manner in hMADS adipocytes. Therefore, the modulation of colonic and circulating acetate may be an important target to modulate human adipose tissue lipid metabolism.