Advances in the molecular biology of ageing, insulin resistance, inflammation, carcinogenesis and caloric restriction have elucidated commonalities relevant to the chronic overnutrition syndrome termed obesity. Not until the expanded acceptance and availability of surgical treatment of obesity ("bariatric surgery") has it been possible to explore the beneficial effects of sustained voluntary weight loss through controlled undernutrition in freely living people. Bariatric surgery is 58 years old and has undergone dramatic improvements recently becoming significantly safer and more accessible owing to the development of minimally invasive approaches and other advances. Furthermore, it is cost-effective compared to all forms of non-operative treatment. Thus older candidates, with more numerous and severe comorbidities are being recruited, increasing the pool of patients who have had operations which extend the otherwise shorter lives of the obese. Here we describe two mechanistically different operations, gastric restrictive and diversionary, and address their risks, complications, side-effects and beneficial outcomes, in aggregate increasing longevity, reducing morbidity and most important: improving health-related quality-adjusted life years.