Microbiome in Lean Individuals: Phenotype-Specific Risks and Outcomes

Many studies provided strong evidence that thinness as a potential individual underweight is an overlooked phenomenon in terms of health risks causality and associated pathologies which are much less explored compared to those associated with overweight and obesity. Disease predisposition linked to low body mass index has been demonstrated for individuals with Flammer Syndrome phenotype. This phenotype is manifested early in life and, therefore, is of great clinical relevance for predictive, preventive and personalised approach in primary healthcare. The transition phase between sub-optimal health condition and clinical manifestation of the disease is the operational timeframe of the reversible damage to health protecting the affected person against disease development and progression (secondary and tertiary care). Association of the FS phenotype and shifted microbiome profiles has been suggested for oral and vaginal microbiome as being linked, in particular, to the stress overload, disturbed microcirculation, Sicca syndrome and delayed/impaired healing. Anorexia nervosa (AN) is considered an extreme case of the FS phenotype. The best acknowledged risk factors predisposing individuals with FS phenotype to AN and AN-associated pathologies are specific behavioural patterns, altered psychosocial functioning, pronounced perfectionism, and thin-ideal internalisation, amongst others. It has been suggested that eating disorders may result from stress-induced maladaptive alterations in neural circuits which regulate feeding as demonstrated in animal models of eating disorders. The chapter provide in-depth analysis between the lean phenotype and microbiota profiles and suggest innovative strategies based on the principles of predictive, preventive and personalised medicine.