The gut microbiome in the fight against obesity: The potential of dietary factors

The effects of chicory inulin-type fructans supplementation on weight management outcomes: systematic review, meta-analysis, and meta-regression of randomized controlled trials

BACKGROUND

Excess body weight and adiposity can adversely affect metabolic health. Prebiotics such as inulin-type fructans (ITFs) from chicory root are known to modulate gut microbiota and may improve body weight regulation.

OBJECTIVES

This study aimed to assess evidence for chicory ITF supplementation to support weight management.

METHODS

Eligible articles (initial search to 2021, updated to February 2023) were searched from EMBASE, MEDLINE (PubMed), and Cochrane Library. Data on primary (body weight) and secondary outcomes [body mass index (BMI), total fat mass, body fat percentage, and waist circumference] were extracted by 2 reviewers independently. Random-effects model using inverse-variance method was used. Subgroup analysis (health status and ITF type) and meta-regression (dose and duration) were evaluated.

RESULTS

A total of 32 eligible studies were included. Chicory ITF significantly reduced body weight [mean difference (MD): -0.97 kg; 95% CI: -1.34, -0.59); n = 1184] compared with placebo. ITF favored overall effects reduction in BMI (MD: -0.39 kg/m2; 95% CI: -0.57, -0.20; n = 985), fat mass (MD: -0.37 kg; 95% CI: -0.61, -0.13; n = 397), waist circumference (MD: -1.03 cm; 95% CI: -1.69, -0.37; n = 604), and for intervention duration of >8 wk, body fat percentage (MD: -0.78%; 95% CI: -1.17, -0.39; n = 488). Except for considerable heterogeneity in body weight (I2: 73%) and body fat percentage (I2: 75%), all other outcomes had negligible to moderate heterogeneity. Significant reduction in body weight, BMI, and waist circumference was evident irrespective of participants' health status. There was minimal evidence that dose, duration, or type of ITF influenced the magnitude of reductions in outcomes.

CONCLUSIONS

Chicory ITF supplementation may benefit weight management by reducing body weight, BMI, fat mass, waist circumference, and, to a certain extent, body fat percentage. This systematic review with meta-analysis was registered at PROSPERO as CRD42020184908.

Role of the Intestine and Its Gut Microbiota in Metabolic Syndrome and Obesity

The metabolic syndrome (MetSyn) is currently one of the biggest global health challenges because of its impact on public health. MetSyn includes the cluster of metabolic disorders including obesity, high blood pressure, hyperglycemia, high triglyceride levels, and hepatic steatosis. Together, these abnormalities increase the cardiovascular risk of individuals and pose a threat to healthcare systems worldwide. To better understand and address this complex issue, recent research has been increasingly focusing on unraveling the delicate interplay between metabolic disorders and the intestines and more specifically our gut microbiome. The gut microbiome entails all microorganisms inhabiting the gastrointestinal tract and plays a pivotal role in metabolic processes and overall health of its host. Emerging evidence proves an association between the gut microbiome composition and aspects of MetSyn, such as obesity. Understanding these relationships is crucial because they offer valuable insights into the mechanisms underlying development and progression of metabolic disorders and possible treatment options. Yet, how should we interpret this relationship? This review focuses on the interplay between the gut and MetSyn. In addition, we have reviewed the existing evidence of the gut microbiome and its association with and impact on metabolic disorders, in an attempt to understand the complex interactions and nature of this association. We also explored potential therapeutic options targeting the gut to modify metabolic disorders and obesity.

Vitamin D intervention as a curative measure for glucose intolerance in obese children and adolescents: a systematic review on randomized control trials

Vitamin D deficiency is associated with obesity and its associated metabolic disorders, as specified in many epidemiological studies. The assertion that vitamin D can mitigate insulin insensitivity in obese children and adolescents lacks adequate empirical substantiation. Thus, the study utilized some clinical trials on vitamin D interventions to examine the impact of vitamin D supplementation on insulin resistance in obese children and adolescents. The literature was extracted by applying the PRISMA method through electronic databases such as Scopus, Science Direct, Medline, the Cochrane Library, and PubMed from 2012 to 2022. All the articles were in English, and the inclusion criteria for each article were based on the study design and the anthropometric and biochemical parameters of the subjects. A total of 572 research articles were acquired, out of which only seven closely adhered to the inclusion criteria of the study. The studies in this systematic review are based on randomized control trials. The age range of the children in this study spans from 2 to 19 years, and the follow-up period ranges from 3 to 12 months. The range of daily vitamin D doses provided varied from 2000 to 10,000 IU. The results indicate that four randomized controlled trials have demonstrated a positive impact on glycemic parameters, such as insulin levels, fasting blood sugar, and insulin resistance, in the subjects following vitamin D treatment. However, the three trials did not provide sufficient evidence to support a statistically significant effect.

CONCLUSION

The present review highlights that a significant proportion of the studies incorporated in the analysis demonstrate that the administration of vitamin D may be a preventive measure in ameliorating insulin resistance among pediatric patients with obesity, but it is advisable to implement a prolonged intervention with a substantial sample size and perform micro-level analysis at the gene level to evaluate the impact of vitamin D treatment.

WHAT IS KNOWN

• Childhood obesity and its associated metabolic disorder is a concerned global problem. • Several studies showed an association of vitamin D deficiency with adiposity- induced metabolicdisorders which are still controversial. This study focused on finding interlink between vitamin Dsupplementation with obesity induced insulin resistance in children and adolescents.

WHAT IS NEW

• This study supports that high dosage of Vitamin D in long term may be protective against insulinresistance in obese paediatric individuals. • A new factor is also reported in the study that vitamin D may alter the composition of gut microbiotawhich represents a compelling approach to the therapeutic management of obesity and diabetes.

Effect of the gut microbiome, plasma metabolome, peripheral cells, and inflammatory cytokines on obesity: a bidirectional two-sample Mendelian randomization study and mediation analysis

Background

Obesity is a metabolic and chronic inflammatory disease involving genetic and environmental factors. This study aimed to investigate the causal relationship among gut microbiota abundance, plasma metabolomics, peripheral cell (blood and immune cell) counts, inflammatory cytokines, and obesity.

Methods

Summary statistics of 191 gut microbiota traits (N = 18,340), 1,400 plasma metabolite traits (N = 8,299), 128 peripheral cell counts (blood cells, N = 408,112; immune cells, N = 3,757), 41 inflammatory cytokine traits (N = 8,293), and 6 obesity traits were obtained from publicly available genome-wide association studies. Two-sample Mendelian randomization (MR) analysis was applied to infer the causal links using inverse variance-weighted, maximum likelihood, MR-Egger, weighted median, weighted mode, and Wald ratio methods. Several sensitivity analyses were also utilized to ensure reliable MR results. Finally, we used mediation analysis to identify the pathway from gut microbiota to obesity mediated by plasma metabolites, peripheral cells, and inflammatory cytokines.

Results

MR revealed a causal effect of 44 gut microbiota taxa, 281 plasma metabolites, 27 peripheral cells, and 8 inflammatory cytokines on obesity. Among them, five shared causal gut microbiota taxa belonged to the phylum Actinobacteria, order Bifidobacteriales, family Bifidobacteriaceae, genus Lachnospiraceae UCG008, and species Eubacterium nodatum group. Furthermore, we screened 42 shared causal metabolites, 7 shared causal peripheral cells, and 1 shared causal inflammatory cytokine. Based on known causal metabolites, we observed that the metabolic pathways of D-arginine, D-ornithine, linoleic acid, and glycerophospholipid metabolism were closely related to obesity. Finally, mediation analysis revealed 20 mediation relationships, including the causal pathway from gut microbiota to obesity, mediated by 17 metabolites, 2 peripheral cells, and 1 inflammatory cytokine. Sensitivity analysis represented no heterogeneity or pleiotropy in this study.

Conclusion

Our findings support a causal relationship among gut microbiota, plasma metabolites, peripheral cells, inflammatory cytokines, and obesity. These biomarkers provide new insights into the mechanisms underlying obesity and contribute to its prevention, diagnosis, and treatment.