Epidemiology of Adult Obesity

  • Obesity is a complex chronic disease, characterised by dysfunctional or excess body fat (adiposity), that impairs health.
  • Excess or dysfunctional adiposity increases the risk of health complications, such as heart disease, cancer, stroke, type 2 diabetes, non-alcoholic fatty liver disease, as well as mental health, mood, anxiety and eating disorders. It can also impair health-related quality of life and reduce life expectancy.
  • From an epidemiological perspective, obesity is classified as a body mass index (BMI; weight/height2) exceeding 30 kg/m2, and further sub-classified into class 1 (BMI 30 kg/m2 – 34.9 kg/m2), class 2 (BMI 35 kg/m2 – 39.9 kg/m2) and class 3 (BMI ≥ 40 kg/m2) obesity.
  • In Ireland, the prevalence of BMI-classified obesity in adults has doubled in the last three decades, affecting 23% of Irish adults in 20191. The percentage of the Irish population with class 2 obesity increased significantly between 1990 and 2011 from 1.4% to 3.6%2. Overweight (classified as BMI 25 kg/m2 – 29.9 kg/m2) affects an additional 37% of adults in Ireland2. Over the same 30-year time period, measures of abdominal adiposity increased concurrently, and are associated with significant increases in health risk.
  • Health professionals should not rely solely on BMI to predict an individual’s health risk but use it in conjunction with other screening and assessment tools.
  • Weight bias, stigma and discrimination are pervasive in society and the healthcare system and result in the unjust treatment of individuals living with obesity.
  • The causes of and contributors to obesity are dynamic and complex and extend well beyond the individual. Established contributors include socio-economic status, health inequalities, sex, ethnicity, access to healthcare, genetics, food and built environments.
  • There is a strong socio-economic gradient to obesity prevalence, and large inequalities in health status exist according to socio-economic status in Ireland. People living in deprived areas are more likely to have a BMI > 25 kg/m2 (65% vs. 55%) and report a chronic health condition (42% vs. 35%) compared to those in more affluent areas. Among those aged < 35 years, 50% of those living in deprived areas have BMI-classified overweight or obesity, compared to 37% of those living in more affluent areas1.
  • Obesity affects individuals, families and society with a significant economic burden, mainly relating to increases in healthcare costs and lost productivity. In 2017, the lifetime costs of obesity on the island of Ireland were estimated at €7.2 billion, with €4.6 billion relating to the Republic of Ireland3.
  • Successful management (i.e., prevention and treatment) of obesity will require collective effort at the policy, health system, community and individual levels.
  • There is a need for continued and focused investment in research funding to support the scientific understanding of obesity. This includes non-experimental research on the wider complex obesity system, which incorporates biopsychosocial and environmental drivers, and experimental research to develop and test interventions to prevent, manage and treat obesity. Research on how best to implement evidence-based practice and policy is a priority.
  1. Healthcare professionals can recognise and treat obesity as a complex chronic disease, characterised by abnormal or excessive body fat (adiposity), that impairs health, with increased risk of premature morbidity and mortality (Level 2b, Grade B)4-9
  2. The development of evidence-informed strategies at the health system and policy levels can be directed at managing obesity in adults (Level 2b, Grade B)5-9.
  3. Continued longitudinal national and regional surveillance of obesity that includes self-reported and measured data (i.e., heights, weights, waist circumference) may be collected on a regular basis (Level 2b, Grade B)5-9.

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