Abstract
Studies in rodent models have shown that alterations in drinking water pH affect both the composition of the gut microbiota and host glucose regulation. To explore a potential impact of electrochemically reduced alkaline (pH ≈ 9) versus neutral (pH ≈ 7) drinking water (2 L/day) on human intestinal microbiota and host glucose metabolism we conducted a randomized, non-blinded, cross-over study (two 2-week intervention periods, separated by a 3-week wash-out) in 29 healthy, non-smoking Danish men, aged 18 to 35 years, with a body mass index between 20.0 to 27.0 kg m-2. Volunteers were ineligible if they had previously had abdominal surgery, had not been weight stabile for at least two months, had received antibiotic treatment within 2 months, or had a habitual consumption of caloric or artificially sweetened beverages in excess of 1 L/week or an average intake of alcohol in excess of 7 units/week. Microbial DNA was extracted from faecal samples collected at four time points, before and after each intervention, and subjected to 16S rRNA gene amplicon sequencing (Illumina MiSeq, V4 region). Glycaemic regulation was evaluated by means of an oral glucose tolerance test.No differential effect of alkaline versus neutral drinking water was observed for the primary outcome, overall gut microbiota diversity as represented by Shannon’s index. Similarly, neither a differential effect on microbiota richness or community structure was observed. Nor did we observe a differential effect on the abundance of individual operational taxonomic units (OTUs) or genera. However, analyses of within period effects revealed a significant (false discovery rate ≤5%) increase in the relative abundance of 9 OTUs assigned to order Clostridiales, family Ruminococcaceae, genus Bacteroides, and species Prevotella copri, indicating a potential effect of quantitative or qualitative changes in habitual drinking habits. An increase in the concentration of plasma glucose at 30 minutes and the incremental area under the curve of plasma glucose from 0 30 and 0 120 minutes, respectively, was observed when comparing the alkaline to the neutral intervention. However, results did not withstand correction for multiplicity. In contrast to what has been reported in rodents, a change in drinking water pH had no impact on the composition of the gut microbiota or glucose regulation in young male adults. The study is registered at www.clinicaltrials.gov (NCT02917616).
Highlights
The incidence of type 2 diabetes (T2D) is increasing and 592 million people worldwide are projected to be affected by the disease by 2035, which makes T2D a major public-health challenge[1]
It has been demonstrated that dietary nutrient composition is a strong determinant of intestinal ecology[12], with dietary changes being mirrored by compositional changes within days[13], it remains elusive whether the microbial features associated with insulin resistance and T2D in humans are induced by specific dietary patterns, including acidogenic diets
Taken together these observations suggest that the effects of changes in drinking water pH reported by Wolf et al and Sofi et al may in part be influenced by mechanisms affecting insulin resistance in addition to augmented autoimmune insulitis
Summary
The incidence of type 2 diabetes (T2D) is increasing and 592 million people worldwide are projected to be affected by the disease by 2035, which makes T2D a major public-health challenge[1]. Differences in baseline gut microbiota, along with difference in other environmental circumstances, have been proposed as an explanation for the conflicting results regarding diabetes incidence and rate of progression[16,17] Both studies showed substantial differences in the gut microbiota of mice drinking acidic and neutral water, demonstrating that drinking water pH can have a profound impact on the gut microbial community. A recent study has shown that NOD mice develop insulin resistance, with hepatic insulin resistance being present already in the pre-diabetic phase and muscle insulin sensitivity being impaired as early as three days after onset of diabetes[19] Taken together these observations suggest that the effects of changes in drinking water pH reported by Wolf et al and Sofi et al may in part be influenced by mechanisms affecting insulin resistance in addition to augmented autoimmune insulitis
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