Microb Biotechnol
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Classical medical research is disease focused and still defines health as absence of disease. Languages, however, associate a positive concept of wholeness with health as does the WHO health definition. Newer medical health definitions emphasize the capacity to adapt to changing external and internal circumstances. ⋯ Of central social and economic importance is the question whether healthy ageing can be achieved. This concept hinges on theories on the biological basis of lifespan determination and whether negligible senescence and the compression of morbidity can be achieved in human societies. Since the health impact of the human gut microbiome is currently a topical research area, microbiologists should be aware of the problems in defining health.