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Sex, hormones, obesity affect diversity, composition of gut microbiota

Stephen Padilla
06 Aug 2018
The composition of gut microbiota is critical not only for regulating the immune system, but also for maintaining mental health and combating extrinsic pathogens.

The combined effects of obesity, sex and sex hormone concentrations influence the diversity and composition of gut microbiota, presenting with specific abnormalities in women with polycystic ovary syndrome (PCOS), suggests a recent study.

“Intervention studies designed to determine the causality of these associations may permit targeting gut microbiota as putative diagnostic and therapeutic targets for PCOS, obesity and associated metabolic comorbidities,” researchers said.

Women had reduced bacterial α diversity compared with men, while obese patients with PCOS had reduced β diversity. Women with PCOS presented with specific abnormalities in gut microbiota, which consisted of an increased abundance of the Catenibacterium and Kandleria genera. [J Clin Endocrinol Metab 2018;103:2552-2562]

Indexes of bacterial diversity and the abundance of several bacterial genera were positively associated with serum androgen concentration and negatively associated with oestradiol levels when considering all participants.

The influence of sex on bacterial α diversity in the gut microbiota was not present in another study, which showed no differences in α bacterial diversity between men and women. [PLoS One 2016;11:e0154090]

However, the inclusion of postmenopausal women in the said study might have obscured the sexual dimorphism in the diversity of gut microbiota and possible influences of sex hormones indicated in the present analysis, according to researchers.

“Moreover, because α diversity showed positive correlations with testosterone levels and ratio of free testosterone to free oestradiol and negative correlations with oestradiol concentrations, our study further suggests that androgens and oestrogens might be involved in the sexual dimorphism reported here,” they added.

However, the present data derived from a cross-sectional study cannot clarify the causality of such associations. There exists a possibility that gut microbes play a role in the regulation of sex hormones and, conversely, that sex hormones modify microbial diversity, according to researchers. [Immunity 2013;39:400-412]

Furthermore, obesity heavily influenced the changes in β bacterial diversity of gut microbiota, which contrasted with the findings in α diversity. This exemplified the complex interactions among sex, sex hormones and obesity on gut bacterial diversity, which was particularly significant in the subset of women with PCOS.

“Even though the current literature on the effect of obesity on bacterial diversity yielded conflicting results, our study addressed the role of sex and sex hormones on such an effect,” researchers said. [Nature 2012;489:220-230; Nature 2013;500:541-546; FEBS Lett 2014;588:4223-4233; BMC Gastroenterol 2015;15:100]

“[T]his issue is of paramount importance because gonadal dysfunction, consisting of androgen excess in women and androgen deficiency in men, is prevalent in obese persons,” they added. [Hum Reprod 2014;29:2083-2091; Hum Reprod Update 2017;23:390-408]

The present cross-sectional study included 15 women with PCOS, 16 nonhyperandrogenic control women and 15 control men. Participants were classified as nonobese (<30 kg/m2) or obese (≥30 kg/m2) according to their body mass index.

Diet was standardized for 3 consecutive days (at least 300 g of carbohydrates per day) followed by faecal sampling and a standard 75-g oral glucose tolerance test.

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