Obesity and Nutrition in Critical Illness: The role of nutrition in obese critically ill patients and an overview of the clinical guidelines for nutrition provision in this patient population

The World Health Organization defines obesity as an excess of abdominal fat that poses an increased risk to health. Characterised by a body mass index (BMI) ≥30 kg/m2, obesity rates have tripled since 1975, and in 2016, 650 million people worldwide were obese (who.int/ news-room/fact-sheets/detail/obesityand- overweight). In the largest analysis of international nutrition provision during critical illness (n=17,154), more than half of the patients were overweight or obese, and the mean and standard deviation (SD) BMI was 27 (8) kg/m2 (Ridley et al. 2018). Moreover, in the most recently published and largest critical care enteral nutrition trial ever conducted, the impact of higher energy enteral feeding versus standard care nutrition on 90-day survival was investigated (3957 patients from 46 ICUs in Australia and New Zealand). The mean (SD) BMI in the intervention and standard care groups was 29.2 (7.7) kg/ m2 and 29.3 (7.9) kg/m2 respectively (Chapman et al. 2018). Obesity is associated with increased morbidity in the general population, but the impact of obesity in critical illness on clinical outcomes is more complex. While obesity is associated with increased morbidity and resource utilisation, a J-shaped relationship exists where overweight and moderate obesity is protective of mortality compared to a normal BMI or severe obesity [known as the obesity paradox] (Arroyo-Johnson and Mincey 2016; Schetz et al. 2019).