The inside story

Any story about a human's microbes tends to invoke impressive numbers. Take the 10 trillion or so microbial cells living in the gut, which exceed the number of human cells by 10 to 1. Between them, they harbour millions of genes, compared with the paltry 20,000 estimated in the human genome. To say that you are outnumbered is a massive understatement.

There is strength in numbers; so much so, in fact, that some biologists regard a human as a 'superorganism' — a community that adds up to more than the sum of its parts. The body itself is merely one, albeit encompassing, component.

Microbes in the human gut may offer a wealth of information about health and disease

Recent studies have suggested that the gut microbiota may have a role in obesity through the regulation of energy metabolism by several mechanisms (that is, energy harvest from the diet, regulation of fat storage, lipogenesis and fatty oxidation, modulation of afferent gastrointestinal peptide hormones, induction of metabolic endotoxemia).

All these findings lead to the concept of human beings as a ‘superorganism’ in which the metabolism is the resultant of the integration of the host metabolic processes with the microbiome ones. The symbiotic metabolic complexity of the individual host–microbiome co-metabolism is likely to be reflected in a specific chemical signature of biofluids.