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On Orthorexia Nervosa: A Systematic Review of Reviews.
Ng, QX, Lee, DYX, Yau, CE, Han, MX, Liew, JJL, Teoh, SE, Ong, C, Yaow, CYL, Chee, KT
Psychopathology. 2024;(4):1-14
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Abstract
INTRODUCTION Orthorexia nervosa (ON), characterized by a pathological preoccupation with "extreme dietary purity," is increasingly observed as a mental health condition among young adults and the general population. However, its diagnosis is not formally recognized and has remained contentious. OBJECTIVE In this systematic review, we attempt to overview previous reviews on ON, focusing on the methodological and conceptual issues with ON. This would serve both as a summary and a way to highlight gaps in earlier research. METHODS This systematic review took reference from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines, and using combinations of the search terms ("orthorexia" OR "orthorexia nervosa" OR "ON") AND ("review" OR "systematic review" OR "meta-analysis"), a literature search was performed on EMBASE, Medline and PsycINFO databases from inception up to October 31, 2023. Articles were included if (1) they were written or translated into English and (2) contained information pertaining to the diagnostic stability or validity of ON, or instruments used to measure ON symptoms and behaviors. Only review articles with a systematic literature search approach were included. RESULTS A total of 22 reviews were qualitatively reviewed. Several studies have reported variable prevalence of ON and highlighted the lack of thoroughly evaluated measures of ON with clear psychometric properties, with no reliable estimates. ORTO-15 and its variations such as ORTO-11, ORTO-12 are popularly used, although their use is discouraged. Existing instruments lack specificity for pathology and several disagreements on the conceptualization and hence diagnostic criteria of ON exist. DISCUSSION Previous reviews have consistently highlighted the highly variable (and contradictory) prevalence rates with different instruments to measure ON, lack of stable factor structure and psychometrics across ON measures, paucity of data on ON in clinical samples, and a need for a modern re-conceptualization of ON. The diagnosis of ON is challenging as it likely spans a spectrum from "normal" to "abnormal," and "functional" to "dysfunctional." "Non-pathological" orthorexia is not related to psychopathological constructs in the same way that ON is.
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A systematic review of the association between environmental risk factors and the development of irritable bowel syndrome.
Ng, QX, Yaow, CYL, Moo, JR, Koo, SWK, Loo, EXL, Siah, KTH
Journal of gastroenterology and hepatology. 2024
Abstract
BACKGROUND AND AIM Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with roots in genetic, immune, psychological, and dietary factors. Recently, the potential correlation between environmental exposures, such as air pollution, and IBS has gained attention. This review aimed to systematically examine existing studies on environmental factors associated with IBS, elucidating this interplay and guiding future research. METHODS A literature search was conducted in Medline, EMBASE, Scopus, and Cochrane databases from database inception to October 10, 2023, using the keywords "Irritable Bowel" or IBS or "Irritable Colon" or "Mucous Colitis" or "Spastic Colitis" or "Spastic Colon" AND "environment* exposure*". Studies were included if they were original, published in English, described defined environmental exposure(s), and had documented diagnosis of IBS. For the purposes of this review, articles reporting physical (e.g. radiation and climate change), biological (e.g. bacteria and viruses), and chemical (e.g. harmful gases) exposures were included while psychological and dietary factors, which have been reviewed in detail elsewhere, are outside of the scope. RESULTS A total of seven studies focusing on air quality, microbial exposure, and other environmental factors were reviewed. Studies highlighted a potential association between air pollutants and increased IBS incidence. Microbial exposure, post-natural disaster or due to poor sanitation, was linked to IBS development and gut dysbiosis. Other exposures, such as early pet ownership, were also associated with IBS risk. CONCLUSION Existing research demonstrates an epidemiologic relationship between environmental exposures and the development of IBS. Further research is needed to understand these associations.
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Examining the Association between Coffee Intake and the Risk of Developing Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis.
Lee, JY, Yau, CY, Loh, CYL, Lim, WS, Teoh, SE, Yau, CE, Ong, C, Thumboo, J, Namasivayam, VSO, Ng, QX
Nutrients. 2023;15(22)
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Irritable bowel syndrome (IBS) is a highly prevalent disorder of brain–gut interaction with a significant impact on quality of life and social functioning. Diet has been implicated in the pathophysiology of IBS as well as disease flares. A significant proportion of IBS patients experience food-related symptoms associated with consuming or eliminating certain foods. This study's aim was to determine if there is an association between coffee intake and the likelihood of developing IBS. This study was a systematic review and meta-analysis of eight studies with 432,022 participants. Results showed that coffee drinkers (any intake) may have a decreased risk of developing IBS compared to controls. However, these findings must be interpreted in light of several shortcomings. Authors concluded that future studies should (1) prioritise high-quality prospective cohort studies with well-documented coffee consumption (and exposure) and track the development of incident IBS in previously healthy individuals over time, and (2) investigate biological mechanisms.
Abstract
Irritable bowel syndrome (IBS) is a highly prevalent disorder of brain-gut interaction with a significant impact on quality of life. Coffee is a widely consumed beverage with numerous bioactive compounds that have potential effects on human health and disease states. Current studies on the effect of regular coffee consumption on the risk of developing IBS symptoms have yielded conflicting results. This systematic review and meta-analysis aimed to determine whether coffee intake is associated with developing IBS. A systematic literature search was performed in three electronic databases, namely PubMed, EMBASE, and The Cochrane Library, from inception until 31 March 2023. All original studies reporting associations between coffee intake and IBS were considered for inclusion. Odds ratios (ORs) were calculated for each study, and estimates were pooled, and where appropriate, 95% confidence intervals (95% CI) and p-values were calculated. Eight studies comprising 432,022 patients were included in the final meta-analysis. Using a fixed-effects model, coffee drinkers (any intake) had a reduced likelihood of developing IBS compared to controls, with a pooled OR of 0.84 (95% CI: 0.80 to 0.84). Sensitivity analysis confirmed the stability of the estimates. Future research should prioritise prospective cohort studies that are robust and closely track the development of incident IBS in previously healthy individuals.
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What Has Longitudinal 'Omics' Studies Taught Us about Irritable Bowel Syndrome? A Systematic Review.
Ng, QX, Yau, CE, Yaow, CYL, Chong, RIH, Chong, NZ, Teoh, SE, Lim, YL, Soh, AYS, Ng, WK, Thumboo, J
Metabolites. 2023;(4)
Abstract
Irritable bowel syndrome is a prototypical disorder of the brain-gut-microbiome axis, although the underlying pathogenesis and mechanisms remain incompletely understood. With the recent advances in 'omics' technologies, studies have attempted to uncover IBS-specific variations in the host-microbiome profile and function. However, no biomarker has been identified to date. Given the high inter-individual and day-to-day variability of the gut microbiota, and a lack of agreement across the large number of microbiome studies, this review focused on omics studies that had sampling at more than one time point. A systematic literature search was performed using various combinations of the search terms "Irritable Bowel Syndrome" and "Omics" in the Medline, EMBASE, and Cochrane Library up to 1 December 2022. A total of 16 original studies were reviewed. These multi-omics studies have implicated Bacteroides, Faecalibacterium prausnitzii, Ruminococcus spp., and Bifidobacteria in IBS and treatment response, found altered metabolite profiles in serum, faecal, or urinary samples taken from IBS patients compared to the healthy controls, and revealed enrichment in the immune and inflammation-related pathways. They also demonstrated the possible therapeutic mechanisms of diet interventions, for example, synbiotics and low fermentable oligosaccharides, disaccharides, monosaccharides, and polyol (FODMAP) diets on microbial metabolites. However, there was significant heterogeneity among the studies and no uniform characteristics of IBS-related gut microbiota. There is a need to further study these putative mechanisms and also ensure that they can be translated to therapeutic benefits for patients with IBS.
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Effect of Probiotic Supplementation on Gut Microbiota in Patients with Major Depressive Disorders: A Systematic Review.
Ng, QX, Lim, YL, Yaow, CYL, Ng, WK, Thumboo, J, Liew, TM
Nutrients. 2023;(6)
Abstract
There is accumulating evidence on the beneficial effects of probiotic supplementation for patients with depressive disorders. However, prior reviews on the topic have largely focused on clinical effectiveness with limited emphasis on the underlying mechanisms of action and effects of probiotics on gut microbiota. In accordance with PRISMA guidelines, a systematic literature search of Medline, EMBASE and the Cochrane Library using combinations of the key words, ("depress*" OR "MDD" OR "suicide"), ("probiotic" OR "Lactobacillus" OR "Bifidobacterium") AND ("gut" OR "gut micr*" OR "microbiota"), as well as grey literature was performed. We found seven clinical trials involving patients with major depressive disorder (MDD). The small number of studies and heterogeneous sources of data precluded meta-analysis. Most trials (other than one open-label trial) had a low-to-moderate risk of bias, which was largely due to a lack of control for the effects of diet on gut microbiota. Probiotic supplementation yielded only modest effects on depressive symptoms and there were no consistent effects on gut microbiota diversity, and in most instances, no significant alterations in gut microbiota composition were observed after four to eight weeks of probiotic intervention. There is also a lack of systematic reporting on adverse events and no good longer-term data. Patients with MDD may require a longer time to show clinical improvement and the microbial host environment may also need longer than eight weeks to produce significant microbiota alterations. To advance this field, further larger-scale and longer-term studies are required.
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Vitamin D supplementation for irritable bowel syndrome: A systematic review and meta-analysis.
Chong, RIH, Yaow, CYL, Loh, CYL, Teoh, SE, Masuda, Y, Ng, WK, Lim, YL, Ng, QX
Journal of gastroenterology and hepatology. 2022;(6):993-1003
Abstract
BACKGROUND AND AIM Irritable bowel syndrome (IBS) is a prevalent and complex gastrointestinal disorder characterized by chronic abdominal pain and altered bowel habits. Observational studies have suggested a relationship between serum vitamin D levels and IBS symptoms. This systematic review and meta-analysis aimed to investigate the clinical effects of vitamin D supplementation on IBS symptom severity and quality of life (QoL) measures. METHODS Medline, Embase, Scopus, Web of Science, and The Cochrane Library databases were systematically searched. Data abstraction and quality assessment were conducted by four authors independently, and discrepancies were resolved through consensus from the senior author. Continuous data were pooled with standardized mean difference (SMD) using the DerSimonian and Laird's random-effects model. Sensitivity analysis by risk of bias and potentially "predatory" publication were performed as well. RESULTS A total of 685 patients across eight studies were included in the meta-analysis. Vitamin D supplementation significantly improved IBS symptom severity scale scores, with a SMD of -0.77 (95% confidence interval [CI] -1.47 to -0.07, P = 0.04, I2 = 91%). Improvements in IBS-QoL scores were also observed, albeit not statistically significant (SMD 0.54; 95% CI -0.34 to 1.41, P = 0.15, I2 = 87%). However, small sample sizes, a relatively young study population, limited ethnicities, and varied vitamin D dosing strategies across the studies were notable limitations. CONCLUSIONS Vitamin D supplementation could be part of our clinical armamentarium when managing IBS patients due to the potential efficacy and good safety profile. Further randomized, controlled trials are required to confirm the therapeutic effects.
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Effects of Astaxanthin Supplementation on Skin Health: A Systematic Review of Clinical Studies.
Ng, QX, De Deyn, MLZQ, Loke, W, Foo, NX, Chan, HW, Yeo, WS
Journal of dietary supplements. 2021;(2):169-182
Abstract
Astaxanthin (AST), a naturally-occurring keto-carotenoid found in several species of bacteria and microalgae, has demonstrated diverse biological activities in vitro and in vivo. There is growing commercial interest in the application of astaxanthin in nutraceuticals and cosmeceuticals, due to its purported photoprotective, DNA repair, antioxidant, and anti-inflammatory benefits. This systematic review therefore aimed to summarize current clinical evidence on the effects of astaxanthin supplementation on skin health. Using the following combinations of broad Major Exploded Subject Headings (MesH) terms or text words [astaxanthin OR AST OR ASX OR carotenoid OR xanthophyll] AND [skin OR derm*], a comprehensive search of PubMed, EMBASE, Medline, Clinicaltrials.gov, and Google Scholar databases found a total of eleven clinical studies. There were six randomized, placebo-controlled, double-blind trials, while the rest were prospective, open-label studies. In many of the randomized, controlled trials reviewed, AST supplementation improved skin texture, appearance (wrinkles), and moisture content at the end of the study period. AST also appeared to protect against UV-induced skin damage. No serious adverse events were reported in any of the studies. However, most available studies had a relatively small sample size and were conducted on healthy Japanese females. Many of the studies were also funded by commercial entities, with potential conflicts of interests. This was difficult to account for in our analyses. Overall, there is some clinical data to support the benefits of astaxanthin supplementation (in the range of 3 to 6 mg/d) on skin health, especially for photoaged skin.
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A systematic review of the clinical use of Withania somnifera (Ashwagandha) to ameliorate cognitive dysfunction.
Ng, QX, Loke, W, Foo, NX, Tan, WJ, Chan, HW, Lim, DY, Yeo, WS
Phytotherapy research : PTR. 2020;(3):583-590
Abstract
Many developed countries are experiencing a rapidly "greying" population, and cognitive decline is common in the elderly. There is no cure for dementia, and pharmacotherapy options to treat cognitive dysfunction provide limited symptomatic improvements. Withania somnifera (Ashwagandha), a popular herb highly valued in Ayurvedic medicine, has often been used to aid memory and cognition. This systematic review thus aimed to evaluate the clinical evidence base and investigate the potential role of W. somnifera in managing cognitive dysfunction. Using the following keywords [withania somnifera OR indian ginseng OR Ashwagandha OR winter cherry] AND [brain OR cognit* OR mental OR dementia OR memory], a comprehensive search of PubMed, EMBASE, Medline, PsycINFO and Clinicaltrials.gov databases found five clinical studies that met the study's eligibility criteria. Overall, there is some early clinical evidence, in the form of randomized, placebo-controlled, double-blind trials, to support the cognitive benefits of W. somnifera supplementation. However, a rather heterogeneous study population was sampled, including older adults with mild cognitive impairment and adults with schizophrenia, schizoaffective disorder, or bipolar disorder. In most instances, W. somnifera extract improved performance on cognitive tasks, executive function, attention, and reaction time. It also appears to be well tolerated, with good adherence and minimal side effects.
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A Systematic Review of the Role of Prebiotics and Probiotics in Autism Spectrum Disorders.
Ng, QX, Loke, W, Venkatanarayanan, N, Lim, DY, Soh, AYS, Yeo, WS
Medicina (Kaunas, Lithuania). 2019;(5)
Abstract
Background: Autism spectrum disorder (ASD) is a complex developmental condition typically characterized by deficits in social and communicative behaviors as well as repetitive patterns of behaviors. Despite its prevalence (affecting 0.1% to 1.8% of the global population), the pathogenesis of ASD remains incompletely understood. Patients with ASD are reported to have more frequent gastrointestinal (GI) complaints. There is some anecdotal evidence that probiotics are able to alleviate GI symptoms as well as improve behavioral issues in children with ASD. However, systematic reviews of the effect of prebiotics/probiotics on ASD and its associated symptoms are lacking. Methods: Using the keywords (prebiotics OR probiotics OR microbiota OR gut) AND (autism OR social OR ASD), a systematic literature search was conducted on PubMed, EMBASE, Medline, Clinicaltrials.gov and Google Scholar databases. The inclusion criteria were original clinical trials, published in English between the period 1st January 1988 and 1st February 2019. Results: A total of eight clinical trials were systematically reviewed. Two clinical trials examined the use of prebiotic and/or diet exclusion while six involved the use of probiotic supplementation in children with ASD. Most of these were prospective, open-label studies. Prebiotics only improved certain GI symptoms; however, when combined with an exclusion diet (gluten and casein free) showed a significant reduction in anti-sociability scores. As for probiotics, there is limited evidence to support the role of probiotics in alleviating the GI or behavioral symptoms in children with ASD. The two available double-blind, randomized, placebo-controlled trials found no significant difference in GI symptoms and behavior. Conclusion: Despite promising preclinical findings, prebiotics and probiotics have demonstrated an overall limited efficacy in the management of GI or behavioral symptoms in children with ASD. In addition, there was no standardized probiotics regimen, with multiple different strains and concentrations of probiotics, and variable duration of treatments.
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A Systematic Review of the Effect of Probiotic Supplementation on Schizophrenia Symptoms.
Ng, QX, Soh, AYS, Venkatanarayanan, N, Ho, CYX, Lim, DY, Yeo, WS
Neuropsychobiology. 2019;(1):1-6
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Abstract
BACKGROUND Derangements of the gut microbiome have been linked to increased systemic inflammation and central nervous system disorders, including schizophrenia. This systematic review thus aimed to investigate the hypothesis that probiotic supplementation improves schizophrenia symptoms. METHODS By using the keywords (probiotic OR gut OR microbiota OR microbiome OR yogurt OR yoghurt OR lactobacillus OR bifidobacterium) AND (schizophrenia OR psychosis), a preliminary search of the PubMed, Medline, Embase, Google Scholar, ClinicalTrials.gov, Clinical Trials Register of the Cochrane Collaboration Depression, Anxiety and Neurosis Group (CCDANTR), and Cochrane Field for Complementary Medicine databases yielded 329 papers published in English between January 1, 1960 and May 1, 2018. Attempts were made to search grey literature as well. RESULTS Three clinical studies were reviewed, comparing the use of probiotics to placebo controls. Applying per-protocol analysis and a fixed-effects model, there was no significant difference in schizophrenia symptoms between the group that received probiotic supplementation and the placebo group post-intervention as the standardized mean difference was -0.0884 (95% CI -0.380 to 0.204, p = 0.551). Separate analyses were performed to investigate the effect of probiotic supplementation on positive or negative symptoms of schizophrenia alone. In both instances, no significant difference was observed as well. CONCLUSION Based on current evidence, limited inferences can be made regarding the efficacy of probiotics in schizophrenia. Although probiotics may have other benefits, for example to regulate bowel movement and ameliorate the metabolic effects of antipsychotic medications, the clinical utility of probiotics in the treatment of schizophrenia patients remains to be validated by future clinical studies.
