Colonic Fermentation and Acetate Production in Youth with and without Obesity

The Obesity-Epigenetics-Microbiome Axis: Strategies for Therapeutic Intervention

Obesity (OB) has become a serious health issue owing to its ever-increasing prevalence over the past few decades due to its contribution to severe metabolic and inflammatory disorders such as cardiovascular disease, type 2 diabetes, and cancer. The unbalanced energy metabolism in OB is associated with substantial epigenetic changes mediated by the gut microbiome (GM) structure and composition alterations. Remarkably, experimental evidence also indicates that OB-induced epigenetic modifications in adipocytes can lead to cellular "memory" alterations, predisposing individuals to weight regain after caloric restriction and subsequently inducing inflammatory pathways in the liver. Various environmental factors, especially diet, play key roles in the progression or prevention of OB and OB-related disorders by modulating the GM structure and composition and affecting epigenetic mechanisms. Here, we will first focus on the key role of epigenetic aberrations in the development of OB. Then, we discuss the association between abnormal alterations in the composition of the microbiome and OB and the interplays between the microbiome and the epigenome in the development of OB. Finally, we review promising strategies, including prebiotics, probiotics, a methyl-rich diet, polyphenols, and herbal foods for the prevention and/or treatment of OB via modulating the GM and their metabolites influencing the epigenome.

Comparison of Metabolic Response to Colonic Fermentation in Lean Youth vs Youth With Obesity

Importance

Pediatric obesity is a growing health care burden. Understanding how the metabolic phenotype of youth with obesity may modify the effect of intestinal fermentation on human metabolism is key to designing early intervention.

Objective

To assess whether adiposity and insulin resistance in youth may be associated with colonic fermentation of dietary fibers and its production of acetate, gut-derived hormone secretion, and adipose tissue lipolysis.

Design, Setting, and Participants

Cross-sectional study of youths aged 15 to 22 years with body mass index in the 25th to 75th percentile or higher than the 85th percentile for age and sex throughout the New Haven County community in Connecticut. Recruitment, studies, and data collection occurred from June 2018 to September 2021. Youths were assigned to a lean, obese insulin sensitive (OIS), or obese insulin resistant (OIR) group. Data were analyzed from April 2022 to September 2022.

Exposure

Participants consumed 20 g of lactulose during a continuous 10-hour sodium d3-acetate intravenous infusion to measure the rate of appearance of acetate in plasma.

Main Outcomes and Measures

Plasma was obtained hourly to measure acetate turnover, peptide tyrosine tyrosine (PYY), ghrelin, active glucagon-like peptide 1 (GLP-1), and free fatty acids (FFA).

Results

A total of 44 youths participated in the study (median [IQR] age, 17.5 [16.0-19.3] years; 25 [56.8%] were female; 23 [52.3%] were White). Consequent to lactulose ingestion, there was a reduction of plasma FFA, an improvement of adipose tissue insulin sensitivity index, an increase in colonic acetate synthesis, and an anorexigenic response characterized by an increased plasma concentration of PYY and active GLP-1 and a reduction of ghrelin in the subgroups. Compared with the lean and OIS groups, the OIR group showed a less marked median (IQR) rate of acetate appearance (OIR: 2.00 [-0.86 to 2.69] μmol × kg-1 × min-1; lean: 5.69 [3.04 to 9.77] μmol × kg-1 × min-1; lean vs OIR P = .004; OIS: 2.63 [1.22 to 4.52] μmol × kg-1 × min-1; OIS vs OIR P = .09), a blunted median (IQR) improvement of adipose insulin sensitivity index (OIR: 0.043 [ 0.006 to 0.155]; lean: 0.277 [0.220 to 0.446]; lean vs OIR P = .002; OIS: 0.340 [0.048 to 0.491]; OIS vs OIR P = .08), and a reduced median (IQR) PYY response (OIR: 25.4 [14.8 to 36.4] pg/mL; lean: 51.3 [31.6 to 83.3] pg/mL; lean vs OIR P = .002; OIS: 54.3 [39.3 to 77.2] pg/mL; OIS vs OIR P = .011).

Conclusions and Relevance

In this cross-sectional study, lean, OIS, and OIR youth demonstrated different associations between colonic fermentation of indigestible dietary carbohydrates and the metabolic response, with OIR youth showing minimal metabolic modifications as compared with the other 2 groups.

Trial Registration

ClinicalTrials.gov Identifier: NCT03454828.

Microbiota of the gastrointestinal tract: Friend or foe?

The gut microbiota is currently considered an external organ of the human body that provides important mechanisms of metabolic regulation and protection. The gut microbiota encodes over 3 million genes, which is approximately 150 times more than the total number of genes present in the human genome. Changes in the qualitative and quantitative composition of the microbiome lead to disruption in the synthesis of key bacterial metabolites, changes in intestinal barrier function, and inflammation and can cause the development of a wide variety of diseases, such as diabetes, obesity, gastrointestinal disorders, cardiovascular issues, neurological disorders and oncological concerns. In this review, I consider issues related to the role of the microbiome in the regulation of intestinal barrier function, its influence on physiological and pathological processes occurring in the body, and potential new therapeutic strategies aimed at restoring the gut microbiome. Herewith, it is important to understand that the gut microbiota and human body should be considered as a single biological system, where change of one element will inevitably affect its other components. Thus, the study of the impact of the intestinal microbiota on health should be considered only taking into account numerous factors, the role of which has not yet been fully elucidated.

Roles of gut microbiota and metabolites in overweight and obesity of children

The prevalence of overweight and obesity in children and adolescents is an increasing public health problem. Pediatric overweight and obesity result from multiple factors, including genetic background, diet, and lifestyle. In addition, the gut microbiota and their metabolites play crucial roles in the progression of overweight and obesity of children. Therefore, we reviewed the roles of gut microbiota in overweight/obese children. The relationship between pediatric overweight/obesity and gut metabolites, such as short-chain fatty acids, medium-chain fatty acids, amino acids, amines, and bile acids, are also summarized. Targeting gut microbiota and metabolites might be a promising strategy for interventions aimed at reducing pediatric overweight/obesity.