Lack of efficacy of pomegranate supplementation for glucose management, insulin levels and sensitivity: evidence from a systematic review and meta-analysis

Effects of Pomegranate Extract on Inflammatory Markers and Cardiometabolic Risk Factors in Adults Aged 55-70 Years: A Randomised Controlled Parallel Trial

Background: Chronic inflammation increases morbidity in older adults and significantly impacts healthy ageing. Pomegranate extract (PE), rich in polyphenols, has been suggested to reduce inflammation and could prevent cardiovascular disease. However, there is limited research examining the potential of PE in disease prevention in ageing. Methods: A two-arm double-blind parallel trial was conducted, in which participants received either placebo capsules (maltodextrin) or pomegranate extract (740 mg) daily for 12 weeks. At baseline, week 6, and week 12, anthropometric measurements, blood pressure, and blood samples were collected. Serum inflammatory markers (IL-6, IL-1-α, IL1-β, IL-2, TNF-α, CRP and PAI-1), fasting blood glucose, and lipid levels were also measured. Results: A total of 86 participants met the eligibility criteria, with 76 completing the trial. A significant interaction between treatment and time was observed for the IL-6 (p = 0.02) and IL1-β (p = 0.05) levels, with both parameters significantly decreasing in the PE group. CRP and TNF-α showed a downward trend in the PE group, but it was not statistically significant (p > 0.05). Systolic blood pressure significantly decreased in the PE group (by 5.22 ± 1.26 mmHg (SE), p = 0.04), indicating potential clinical relevance, with diastolic blood pressure showing a similar downward trend (2.94 ± 1.08 mmHg (SE), p = 0.3). Despite being apparently healthy with no diagnosed diseases, a substantial number of participants exhibited elevated levels of inflammatory markers and systolic blood pressure. Conclusions: PE can lower inflammatory markers and blood pressure, which can be high in both normal-weight and overweight older adults, making it a cost-effective measure to promote healthy ageing. Further long-term studies are needed to address the limitations of this 3-month study, including the overrepresentation of normal-weight participants, and to gain a better understanding of the impact of weight on the above-mentioned outcomes.

The effects of pomegranate consumption on glycemic indices in adults: A systematic review and meta-analysis

BACKGROUND AND AIM

Epidemiologic studies have shown that type 2 diabetes (T2D) is more prevalent worldwide; therefore, improving glycemic indices to prevent or control T2D is vital. Randomized controlled trials (RCTs) on the effects of pomegranate consumption on glycemic indices have shown inconsistent results. Therefore, we aim to evaluate the impact of pomegranate consumption on fasting blood glucose (FBG), fasting insulin, hemoglobin A1c (HbA1c), and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) in adults.

METHODS

A systematic literature search was performed using electronic databases, including PubMed, Web of Science, and Scopus, up to May 2023 to identify eligible RCTs evaluating the effect of pomegranate consumption on glycemic indices. Heterogeneity tests of the included trials were performed using the I2 statistic. Random effects models were assessed based on the heterogeneity tests, and pooled data were determined as the weighted mean difference with a 95 % confidence interval.

RESULTS

Of 1999 records, 32 eligible RCTs were included in the current study. Our meta-analysis of the pooled findings showed that pomegranate consumption significantly reduced FBG (WMD: -2.22 mg/dL; 95 % CI: -3.95 to -0.50; p = 0.012), fasting insulin (WMD: -1.06 μU/ml; 95%CI: -1.79 to -0.33; p = 0.004), HbA1c (WMD: -0.22 %; 95% CI: -0.43 to -0.01; p = 0.037), and HOMA-IR (WMD: -0.30; 95%CI: -0.61 to -0.00; p = 0.046).

CONCLUSION

Overall, the results demonstrated that pomegranate consumption benefits glycemic indices in adults. However, further research with long-term interventions is required.

PROSPERO REGISTRATION CODE

CRD42023422780.

Pharmacotherapeutic potential of pomegranate in age-related neurological disorders

Age-related neurological disorders [AND] include neurodegenerative diseases [NDDs] such as Alzheimer's disease [AD] and Parkinson's disease [PD], which are the most prevalent types of dementia in the elderly. It also includes other illnesses such as migraine and epilepsy. ANDs are multifactorial, but aging is their major risk factor. The most frequent and vital pathological features of AND are oxidative stress, inflammation, and accumulation of misfolded proteins. As AND brain damage is a significant public health burden and its incidence is increasing, much has been done to overcome it. Pomegranate (Punica granatum L.) is one of the polyphenol-rich fruits that is widely mentioned in medical folklore. Pomegranate is commonly used to treat common disorders such as diarrhea, abdominal pain, wound healing, bleeding, dysentery, acidosis, microbial infections, infectious and noninfectious respiratory diseases, and neurological disorders. In the current review article, we aimed to summarize the data on the pharmacotherapeutic potentials of pomegranate in ANDs.

Pomegranate fruit pulp polyphenols reduce diet-induced obesity with modulation of gut microbiota in mice

BACKGROUND

Pomegranate is a rich source of polyphenols and has been used as a dietary supplement and pharmaceutical ingredient. This study aimed to investigate the pomegranate fruit pulp polyphenols (PFP) with regard to their anti-obesity activity and gut microbiota-modulating effect in mice. Thirty-six 4-week-old specific pathogen-free C57BL/6J mice (weight: 17.7-20.8 g) were randomly divided into three groups and fed with low-fat diet (10% fat energy), high-fat diet (HFD) (45% fat energy), or HFD supplemented with PFP by intragastric administration for 14 weeks. The obesity-related clinical indicators were investigated, and the composition of fecal microbiota was analyzed by 16S rRNA sequencing.

RESULTS

Our results showed that PFP treatment reduced HFD-induced body weight gain by 35.23% (P < 0.05), steatosis scores by 50% (P < 0.05) and insulin resistance by 56.84% (P < 0.05), compared with the mice fed HFD alone. Moreover, compared with the mice in the HFD group, PFP supplement changed the composition of the gut microbiota, and enriched Akkermansia muciniphila, Parabacteroides distasonis, Bacteroides acidifaciens, Mucispirillum schaedleri and Lachnospiraceae bacterium 28-4, which were negatively correlated with physical biomarkers, including body weight, glucose, triglycerides and total cholesterol.

CONCLUSION

PFP alleviated HFD-induced obesity, insulin resistance and hepatic steatosis in mice, and the changes in the gut microbiota might be one of the potential mechanisms through which PFP improved obesity and obesity-related disorders, eventually benefiting the recipient. © 2021 Society of Chemical Industry.

Pomegranate peel anthocyanins prevent diet-induced obesity and insulin resistance in association with modulation of the gut microbiota in mice

PURPOSE

Pomegranate peels are rich in anthocyanins. The present study aimed to explore the beneficial effects of pomegranate peel anthocyanins (PPA) on obesity and gut microbiota in mice with high-fat diet (HFD)-induced obesity.

METHODS

Specific pathogen-free (SPF) male C57BL/6 J mice were randomly divided into three groups and fed with low-fat diet (LFD, 10% fat energy), HFD (45% fat energy), or HFD supplemented with PPA by intragastric administration for 15 weeks. Body weight and food intake were monitored weekly. The obesity-related biochemical indexes and hepatic gene expression levels were determined. The compositions of the gut microbiota were analyzed by 16S rRNA sequencing, and the association between the gut microbiota and obesity-related indicators was investigated by Spearman correlation analysis.

RESULTS

The results showed that the body weight gain, steatosis scores and insulin resistance index in the PPA group decreased by 27.46%, 56.25%, and 46.07%, respectively, compared to the HFD group. Gene expression analysis indicated that PPA supplement improved the genes expression profiles involved in glucose and lipid metabolism compared with the mice fed HFD alone. Meanwhile, PPA significantly changed the composition of the gut microbiota, which were closely correlated with the obesity-related biomarkers.

CONCLUSION

This study suggested that PPA could be a beneficial treatment option for alleviating HFD-induced obesity and related metabolic disorders by targeting microbiota and lipid metabolism.

Therapeutic Potential of Pomegranate in Metabolic Disorders

Metabolic syndrome and associated disorders have become one of the major challenging health problems over the last decades. Considerable attention has been paid to natural products and herbal medicines for the management of metabolic disorders in recent years. Many studies have investigated the therapeutic effects of different parts (arils, peels, seeds, and flowers) of pomegranate (Punica granatum L.) for the prevention and treatment of this syndrome. This study aims to provide an updated review on the in vitro and in vivo studies as well as clinical trials investigating the effects of pomegranate and its active compounds on different components of metabolic problems such as hyperglycemia, hyperlipidemia, hypertension, as well as obesity over the last two decades. Besides, the key mechanisms by which pomegranate affects these pathogenic conditions are also discussed. The studies show that although pomegranate has promising beneficial effects on diabetes, hypertension, hyperlipidemia, and obesity in various cellular, animal, and clinical models of studies, there are some conflicting results, particularly for hyperglycemic conditions. The main mechanisms include influencing oxidative stress and anti-inflammatory responses. Overall, pomegranate seems to have positive effects on the pathogenic conditions of metabolic syndrome according to the reviewed studies. Although pomegranate is not suggested as the first line of therapy or monotherapy, it could be only used as an adjunctive therapy. Nevertheless, further large and long-term clinical studies are still required.

Ellagic Acid Suppresses ApoB Secretion and Enhances ApoA-1 Secretion from Human Hepatoma Cells, HepG2

The effect of ellagic acid (EA), a naturally occurring polyphenolic compound, on the secretion of apolipoproteins from human hepatocytes, HepG2, was investigated. The levels of apoB and apoA-1 secreted in the cell culture medium were determined by sandwich ELISA. EA did not affect cell viability at the tested concentrations (up to 50 µM). EA suppressed the secretion of apoB and enhanced that of apoA-1 from HepG2 cells. However, cellular apoB levels were increased, suggesting that EA inhibited the trafficking of apoB during the process of secretion. In contrast, the increase in the cellular levels of apoA-1 was consistent with its secreted levels. These results indicate that EA inhibits the secretion of apoB from hepatocytes and increases the secretion of apoA-1. Both of these effects are beneficial for lipoprotein metabolism in the prevention of lifestyle-related diseases. The detailed mechanism underlying these effects of EA on lipoprotein metabolism should be elucidated in the future, but this naturally occurring polyphenolic compound might be antihyperlipidemic. Based on these results, EA is suggested as a candidate food-derived compound for the prevention of hyperlipidemia.

An 8-week freeze-dried blueberry supplement impacts immune-related pathways: a randomized, double-blind placebo-controlled trial

Background

Blueberries contain high levels of polyphenolic compounds with high in vitro antioxidant capacities. Their consumption has been associated with improved vascular and metabolic health.

Purpose

The objective was to examine the effects of blueberry supplement consumption on metabolic syndrome (MetS) parameters and potential underlying mechanisms of action.

Methods

A randomized double-blind placebo-controlled intervention trial was conducted in adults at risk of developing MetS. Participants consumed 50 g daily of either a freeze-dried highbush blueberry powder (BBP) or a placebo powder for 8 weeks (n = 49). MetS phenotypes were assessed at weeks 0, 4 and 8. Fasting blood gene expression profiles and plasma metabolomic profiles were examined at baseline and week 8 to assess metabolic changes occurring in response to the BBP. A per-protocol analysis was used.

Results

A significant treatment effect was observed for plasma triglyceride levels that was no longer significant after further adjustments for age, sex, BMI and baseline values. In addition, the treatment*time interactions were non-significant therefore suggesting that compared with the placebo, BBP had no statistically significant effect on body weight, blood pressure, fasting plasma lipid, insulin and glucose levels, insulin resistance (or sensitivity) or glycated hemoglobin concentrations. There were significant changes in the expression of 49 genes and in the abundance of 35 metabolites following BBP consumption. Differentially regulated genes were clustered in immune-related pathways.

Conclusion

An 8-week BBP intervention did not significantly improve traditional markers of cardiometabolic health in adults at risk of developing MetS. However, changes in gene expression and metabolite abundance suggest that clinically significant cardiometabolic changes could take longer than 8 weeks to present and/or could result from whole blueberry consumption or a higher dosage. BBP may also have an effect on factors such as immunity even within a shorter 8-week timeframe.

Clinical trial registration

clinicaltrials.gov, NCT03266055, 2017

Supplementary Information

The online version contains supplementary material available at 10.1186/s12263-021-00688-2.

Polyphenols Rich Diets and Risk of Type 2 Diabetes

Type 2 diabetes is an increasing health concern worldwide. Both genetic and environmental risk factors as improper dietary habits or physical inactivity are known to be crucial in the pathogenesis of type 2 diabetes. Polyphenols are a group of plant-derived compounds with anti-inflammatory and antioxidant properties that are associated with a low prevalence of metabolic conditions characterized by insulin resistance, including obesity, diabetes, and hypertension. Moreover, there is now full awareness that foods that are rich in phytochemicals and polyphenols could play an important role in preserving human cardiovascular health and substantial clinical evidence indicates that regular dietary consumption of such foods affects favorably carbohydrate metabolism. This review briefly summarizes the evidence relating dietary patterns rich in polyphenols with glucose metabolism and highlights the potential benefits of these compounds in the prevention of type 2 diabetes.

A polyphenol-rich dietary pattern improves intestinal permeability, evaluated as serum zonulin levels, in older subjects: The MaPLE randomised controlled trial

BACKGROUND & AIM

Increased intestinal permeability (IP) can occur in older people and contribute to the activation of the immune system and inflammation. Dietary interventions may represent a potential strategy to reduce IP. In this regard, specific food bioactives such as polyphenols have been proposed as potential IP modulator due to their ability to affect several critical targets and pathways that control IP. The trial aimed to test the hypothesis that a polyphenol-rich dietary pattern can decrease serum zonulin levels, an IP surrogate marker involved in tight junction modulation, and can beneficially alter the intestinal microbiota, and IP-associated biochemical and clinical markers in older subjects.

METHODS

A randomised, controlled, cross-over intervention trial was performed. Sixty-six subjects (aged ≥ 60 y) with increased IP based on serum zonulin levels, were randomly allocated to one of the two arms of the intervention consisting of a control diet (C-diet) vs. a polyphenol-rich diet (PR-diet). Each intervention was 8-week long and separated by an 8-week wash out period. At the beginning and at the end of each intervention period, serum samples were collected for the quantification of zonulin and other biological markers. Faecal samples were also collected to investigate the intestinal microbial ecosystem. In addition, anthropometrical/physical/biochemical parameters and food intake were evaluated.

RESULTS

Fifty-one subjects successfully completed the intervention and a high compliance to the dietary protocols was demonstrated. Overall, polyphenol intake significantly increased from a mean of 812 mg/day in the C diet to 1391 mg/day in the PR-diet. Two-way analysis of variance showed a significant effect of treatment (p = 0.008) and treatment × time interaction (p = 0.025) on serum zonulin levels, which decreased after the 8-week PR-diet. In addition, a treatment × time interaction was observed showing a reduction of diastolic blood pressure (p = 0.028) following the PR-diet, which was strongest in those not using antihypertensive drugs. A decrease in both diastolic (p = 0.043) and systolic blood pressure (p = 0.042) was observed in women. Interestingly, a significant increase in fibre-fermenting and butyrate-producing bacteria such as the family Ruminococcaceae and members of the genus Faecalibacterium was observed following the PR intervention. The efficacy of this dietary intervention was greater in subjects with higher serum zonulin at baseline, who showed more pronounced alterations in the markers under study. Furthermore, zonulin reduction was also stronger among subjects with higher body mass index and with insulin resistance at baseline, thus demonstrating the close interplay between IP and metabolic features.

CONCLUSIONS

These data show, for the first time, that a PR-diet can reduce serum zonulin levels, an indirect marker of IP. In addition, PR-diet reduced blood pressure and increased fibre-fermenting and butyrate-producing bacteria. These findings may represent an initial breakthrough for further intervention studies evaluating possible dietary treatments for the management of IP, inflammation and gut function in different target populations. THIS STUDY WAS REGISTERED AT WWW.ISRCTN.

ORG AS

ISRCTN10214981.

Ellagic Acid as a Tool to Limit the Diabetes Burden: Updated Evidence

Oxidative stress contributes not only to the pathogenesis of type 2 diabetes (T2D) but also to diabetic vascular complications. It follows that antioxidants might contribute to limiting the diabetes burden. In this review we focus on ellagic acid (EA), a compound that can be obtained upon intestinal hydrolysis of dietary ellagitannins, a family of polyphenols naturally found in several fruits and seeds. There is increasing research on cardiometabolic effects of ellagitannins, EA, and urolithins (EA metabolites). We updated research conducted on these compounds and (I) glucose metabolism; (II) inflammation, oxidation, and glycation; and (III) diabetic complications. We included studies testing EA in isolation, extracts or preparations enriched in EA, or EA-rich foods (mostly pomegranate juice). Animal research on the topic, entirely conducted in murine models, mostly reported glucose-lowering, antioxidant, anti-inflammatory, and anti-glycation effects, along with prevention of micro- and macrovascular diabetic complications. Clinical research is incipient and mostly involved non-randomized and low-powered studies, which confirmed the antioxidant and anti-inflammatory properties of EA-rich foods, but without conclusive results on glucose control. Overall, EA-related compounds might be potential agents to limit the diabetes burden, but well-designed human randomized controlled trials are needed to fill the existing gap between experimental and clinical research.

Effects of Polyphenols on Insulin Resistance

Insulin resistance (IR) is apparent when tissues responsible for clearing glucose from the blood, such as adipose and muscle, do not respond properly to appropriate signals. IR is estimated based on fasting blood glucose and insulin, but some measures also incorporate an oral glucose challenge. Certain (poly)phenols, as supplements or in foods, can improve insulin resistance by several mechanisms including lowering postprandial glucose, modulating glucose transport, affecting insulin signalling pathways, and by protecting against damage to insulin-secreting pancreatic β-cells. As shown by intervention studies on volunteers, the most promising candidates for improving insulin resistance are (-)-epicatechin, (-)-epicatechin-containing foods and anthocyanins. It is possible that quercetin and phenolic acids may also be active, but data from intervention studies are mixed. Longer term and especially dose-response studies on mildly insulin resistant participants are required to establish the extent to which (poly)phenols and (poly)phenol-rich foods may improve insulin resistance in compromised groups.

The Quality Determination of Selected Commercial Online Purchased Edible Pomegranate Seed Oils With New Argentometric Liquid Chromatography Method

The number of online-purchased dietary supplements of diversified origin is exponentially increasing. Pomegranate seed oils (PSOs)-the main dietary source of conjugated linolenic acids (CLnA)-are available as dietary supplements via the Internet. PSO samples (n = 24) were purchased from Internet shops in Poland and China. Chromatographic techniques (gas chromatography coupled with mass spectroscopy [GC-MS] for fatty acids [FAs], liquid chromatography with fluorescence detection for tocopherols, and high-performance liquid chromatography with photodiode array detection for conjugated FAs) were used. The GC-MS method enabled the quantification of 45 FAs, which indicates its superiority to previously used methods. Argentometric liquid chromatography with pre-column mild alkaline hydrolysis for analysis of structural isomers of CLnA does not need preliminary derivatization into volatile compounds, which ensures the absence of artifacts and enables the analysis of the entire conjugated FA profile. PSO differed with tocopherols and FA profile. Some PSOs contained negligible amounts of CLnA, and because of that they did not meet the criteria of valuable, unadulterated nutraceuticals. Obtained results indicate that online purchased PSO shipped from distant places of origin could have been stored in inadequate conditions (temperature, humidity), which caused i.a. deterioration of oxidative quality. Unregulated online availability of dietary supplements of low oxidative quality and nutritive value as well as their intake may be a risk rather than a benefit for consumers. Argentometric liquid chromatography can be a simple, selective, and sensitive tool for screening of dietary supplements containing conjugated FAs and should be considered as an essential way of quality assurance.