The Gut Microbiome as a Key Determinant of Body Mass Index

Obesity has a complex and incompletely understood pathogenesis, with an underlying interplay between our genetic architecture and obesogenic environment. The public understanding of the development of obesity is shrouded in myth with widespread societal misconceptions, often promoted by (or at least insufficiently countered by) the mass media. This includes ideas that weight gain and obesity stem from human vices and ‘sins’ such as greed, gluttony and sloth. Body Mass Index (BMI) is a highly heritable trait. However, despite reports from recent ‘genome-wide association studies’, only a small proportion of the overall heritability of BMI is known to be lurking within the human genome. Other non-genetic heritable traits may contribute towards BMI. The gut microbiome is an excellent candidate, with complex interlinks with hypothalamic control of appetite and metabolism through both direct and indirect routes that implicate entero-endocrine, autonomic, and neuro-humeral pathways. Furthermore, recent evidence promotes a trans-generational transmission of the gut microbiome from the mother to offspring via both vaginal delivery and breast-feeding. The latter implicates a maternal ‘entero-mammary pathway’ in which the maternal gut microbiota translocate across the gut wall and are transported endogenously to the breast milk. Although maternally derived gut microbiota tend to have a permanence within the gut, other microbiota manifest mutability that responds to changes in lifestyle and diet. We should all strive to optimise a healthy lifestyle and diet that is replete with varied and unprocessed plant-based foods to nurture our gut microbiome. Women of reproductive age should optimise their gut microbiome, particularly pre-conception, ante- and postnatally to enable the establishment of a healthy gut microbiome in their offspring from birth. Finally, we should redouble our efforts to educate the populace on the pathogenesis of obesity, and the role of heritable factors such as genetics and the gut microbiome. Such understanding and insights would help to promote the widespread adoption of healthy lifestyles and diet but also help in the transition from our current dispassionate and stigmatised societal approach to obesity, to one that is epitomised by understanding, support, and compassion towards people living with obesity.