To cut or not to cut : the association between weight loss and cardiometabolic health in adolescents and adults after Roux-en-Y Gastric Bypass

Abstract: Energy cannot be destroyed, and in humans excess energy is stored as fat in adipose tissue. Accumulation of fat is thus the result of a positive energy balance, and obesity is defined as an excess amount of adipose tissue. Obesity can be harmful to the individual because it leads to a protracted disease course that can start as early as in childhood. The goal of all obesity treatments is to reverse the positive energy balance. This thesis investigates one of the means of achieving such a reversal, namely the bariatric Roux-en-Y gastric bypass (RYGB) surgery procedure. Study I investigated the prevalence of bariatric surgery after childhood obesity treatment. By the age of 30, more than one fifth of children treated for childhood obesity were estimated to have underwent bariatric surgery. At the time of surgery, the median age was 20.9 years, and an obesity-related comorbidity was identified in 31.7% of patients before surgery. Study II, building on preliminary results from Study IV, investigated the effect of surgical treatment failure five years after RYGB. The prevalence of surgical treatment failure was 23.1% and in turn associated with and increased likelihood of relapse and incidence of type 2 diabetes, dyslipidemia and hypertension. A model for predicting the risk of surgical treatment failure was developed using measurements from before surgery and one and two years after surgery. The model was tested on parts of this study population and on the population in Study IV. The model was found to be accurate and could prove clinically useful. Study III investigated the effect of RYGB-induced weight loss on cardiorespiratory fitness, functional capacity and body composition in a group of adolescents two years after surgery. The results show that adolescents improve their oxygen uptake and functional capacity and that the weight loss consisted of both fat and non-fat mass. The improvements in oxygen uptake among adolescents may be greater than those reported in adults. Study IV explored the heterogeneity of weight loss up to five years after RYGB in adolescents. Most of the total weight loss was observed during the first year, but it was not equal among participants. Between year one and two, weight regain occurred to varying extents in 40% of participants. By year five, a third of participants met at least one definition of surgical treatment failure (defined as a body mass index of above 35 or 40, losing less than 20% of initial weight, or losing less than 50% of excess weight), which was in turn negatively associated with obesity-related risk markers. In summary, if surgical treatment is delayed into adulthood, it is likely that obesity-related comorbidities will manifest. Roux-en-Y gastric bypass surgery is an effective treatment in inducing weight loss in adolescents. Overall, results are on par with or better than those in adults. However, adolescents were observed to exhibit greater variation in weight loss, and surgical treatment failure can hamper the positive effects of RYGB. The model for predicting surgical treatment failure can be used as a risk assessment tool when monitoring subjects following RYGB and to target those likely in need of additional follow-up and support in order to maintain long-term weight loss.