Microbiome–Gut Dissociation: Investigating the Origins of Obesity

The reduction of excessive weight remains a major public health challenge, with control currently limited to a calorie reduction strategy. Currently, attempts are being made at revisiting the fibre hypothesis based on the African studies of Denis Burkitt, that the lack of dietary fibre in the modern diet was responsible for the occurrence of obesity and many of the other non-communicable diseases of what he called “Western civilization”. However, the dilemma is that Burkitt himself stressed that other peoples of his day, such as the Maasai, remained healthy without consuming such high fibre diets. Equally, the present obesity epidemic is accompanied by diseases of a malfunctioning immune system and of poor mental health that do not seem to be adequately explained simply by a deficiency of dietary fibre. Though unknown in Burkitt’s day, an increasing degradation of a mutualistic intestinal microbiome would offer a better fit to the observed epidemiology, especially if the microbiome is not effectively passed on from mother to child at birth. Taking the broader view, in this article we posit a view of the microbiome as a cofactor of mammalian evolution, in which a maternal microbial inheritance complements the parental genetic inheritance of the animal, both engaging epigenetic processes. As this would require the microbiome to be fully integrated with the animal as it develops into an adult, so we have a meaningful evolutionary role for the microbiome–gut–brain axis. By a failure to correctly establish a microbiome–gut interface, the inhibition of maternal microbial inheritance sets the scene for the future development of non-communicable disease: compromised immune system function on the one hand and dysfunctional gut–brain communication on the other. The basic principle is that the fully functioning, diverse, microbiome achieves interkingdom communication by the generation of messenger chemicals, semiochemicals. It is envisaged that the in situ detection of these as yet ill-defined chemical entities by means of an ingestible sensor would indicate the severity of disease and provide a guide as to its amelioration.