The Science of Obesity

  • The causes of obesity are complex and result from interactions between genetic, biological, behavioural, psychosocial and environmental factors.
  • Obesity is highly heritable. Twin studies show a 50%–80% degree of concordance of body mass index (BMI) and regional fat distribution. A Swedish study of identical twins reared apart showed no correlation of BMI with members of their adopted family, but strong correlation with their twin reared in a different family.
  • The neurobiology of appetite, body weight and energy regulation is complex and mediated by a milieu of hormonal signals from the gut, adipose tissue and other organs, and neural signals which influence eating behaviours. Many of these signalling pathways have been shown to be altered in obesity.
  • Because body weight is homeostatically regulated, when weight loss occurs, physiological adaptations act to drive weight regain. This includes reduction in energy expenditure, and hormonal changes that increase appetite and reduce satiety.
  • Adipose tissue influences the central regulation of energy homeostasis, and excess adiposity can become dysfunctional, with production of proinflammatory cytokines and associated metabolic health complications.
  • Due to individual differences in body composition, body fat distribution and function, the threshold at which excess adiposity impairs health is highly variable among individuals.
  • Emerging areas of research in the science of obesity include brown fat, the gut microbiome and immune system dysregulation.

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