Associations of dietary diversity with the gut microbiome, fecal metabolites, and host metabolism: results from 2 prospective Chinese cohorts

BACKGROUND

Dietary diversity is essential for human health. The gut ecosystem provides a potential link between dietary diversity, host metabolism, and health, yet this mechanism is poorly understood.

OBJECTIVES

Here, we aimed to investigate the relation between dietary diversity and the gut environment as well as host metabolism from a multiomics perspective.

METHODS

Two independent longitudinal Chinese cohorts (a discovery and a validation cohort) were included in the present study. Dietary diversity was evaluated with FFQs. In the discovery cohort (n = 1916), we performed shotgun metagenomic and 16S ribosomal ribonucleic acid (rRNA) sequencing to profile the gut microbiome. We used targeted metabolomics to quantify fecal and serum metabolites. The associations between dietary diversity and the microbial composition were replicated in the validation cohort (n = 1320).

RESULTS

Dietary diversity was positively associated with α diversity of the gut microbiota. We identified dietary diversity-related gut environment features, including the microbial structure (β diversity), 68 microbial genera, 18 microbial species, 8 functional pathways, and 13 fecal metabolites. We further found 332 associations of dietary diversity and related gut environment features with circulating metabolites. Both the dietary diversity and diversity-related features were inversely correlated with 4 circulating secondary bile acids. Moreover, 16 mediation associations were observed among dietary diversity, diversity-related features, and the 4 secondary bile acids.

CONCLUSIONS

These results suggest that high dietary diversity is associated with the gut microbial environment. The identified key microbes and metabolites may serve as hypotheses to test for preventing metabolic diseases.

One Month of Classic Therapeutic Ketogenic Diet Decreases Short Chain Fatty Acids Production in Epileptic Patients

Ketogenic diet (KD), a high fat and very low carbohydrates diet, is used worldwide for the treatment of drug resistant epilepsy but, due to its composition, it might exert an impact on gut health. Even though data of KD effects on intestinal microbiota changes are recently emerging, its influence on the gut environment has been scarcely addressed so far. The aim of this study was to investigate whether 1 month of KD affects the gut environment in epileptic patients, by analyzing short chain fatty acids (SCFA) production and fecal water toxicity. A total of seven patients were enrolled. Stool samples were collected before (T0) and after 1 month of KD (4:1 ketogenic ratio) (T1). SCFA were determined by GC-FID and fecal water toxicity in Caco-2 cell culture by comet assay. Concentrations of SCFA significantly decreased after KD (p < 0.05): in particular, we found a 55% reduction of total SCFA level, a 64% reduction of acetate, 33% of propionate, and 20% of butyrate (p < 0.05). Cytotoxicity of fecal water extracted from stool samples was not significantly altered by diet, while genotoxicity was slightly decreased after KD (p < 0.05). Genotoxicity values were consistent with data previously obtained from a healthy Italian population. The present study suggests that 1 month of KD significantly reduce SCFA production. Since SCFA produced by gut microbiota exert many health promoting effects on either the gut environment or human metabolism, these results open a new branch of investigation into KD effects.

Bifidobacterium fermented milk and galacto-oligosaccharides lead to improved skin health by decreasing phenols production by gut microbiota

A questionnaire survey found that women suffering from abnormal bowel movements have many skin problems such as a high frequency of dry skin. Although there are similarities between the structure and barrier function mechanism of the gut and skin, experimental data are insufficient to show an association between the intestinal environment and skin conditions. Phenols, for example phenol and p-cresol, as metabolites of aromatic amino acids produced by gut bacteria, are regarded as bioactive toxins and serum biomarkers of a disturbed gut environment. Recent studies have demonstrated that phenols disturb the differentiation of monolayer-cultured keratinocytes in vitro, and that phenols produced by gut bacteria accumulate in the skin via the circulation and disrupt keratinocyte differentiation in hairless mice. Human studies have demonstrated that restriction of probiotics elevated serum free p-cresol levels and harmed skin conditions (reduced skin hydration, disrupted keratinisation). In contrast, daily intake of the prebiotic galacto-oligosaccharides (GOS) restored serum free p-cresol levels and skin conditions in adult women. Moreover, a double-blind placebo-controlled trial demonstrated that the daily intake of fermented milk containing the probiotic Bifidobacterium breve strain Yakult and prebiotic GOS reduced serum total phenol levels and prevented skin dryness and disruption of keratinisation in healthy adult women. It is concluded that phenols produced by gut bacteria are one of the causes of skin problems. Probiotics and/or prebiotics, such as B. breve strain Yakult and/or GOS, are expected to help maintain a healthy skin by decreasing phenols production by gut microbiota. These findings support the hypothesis that probiotics and prebiotics provide health benefits to the skin as well as the gut.

An insect gut environment reveals the induction of a new sugar-phosphate sensor system in Bacillus cereus

Bacteria survive under various conditions by sensing stimuli triggering specific adaptive physiological responses, which are often based on membrane-integrated sensors connected to a cytoplasmic regulator. Recent studies reveal that mucus glycans may act as signal molecules for two-component systems involved in intestinal colonization. Bacillus cereus, a human and insect opportunistic pathogen was used to identify bacterial factors expressed in an insect gut infection model. The screen revealed a promoter involved in the expression of a gene with so far unknown functions. A search for gut-related compounds, inducing its transcription, identified glucose-6-phosphate as an activation signal. The gene is part of a five-gene cluster, including a two-component system. Interestingly such five gene loci are conserved in the pathogenic Bacillus group as well as in various Clostridia bacteria and are with analogy to other multi-component sensor systems in enteropathogenic bacteria, such as E. coli. Thus our results provide insights into the function of two-component and auxiliary sensor systems in host-microbe interactions and opens up possible investigations of such systems in other gut associated bacteria.