Studies of obesity-related conditions and procedures and a cost-effectiveness appraisal of a novel treatment.

  • Ibrahim Saad I Al Sumaih

Student thesis: Doctoral ThesisDoctor of Philosophy


Despite the global efforts to confront the increasing prevalence of obesity worldwide, many countries failed to bend or even plateau their uptrend. Researchers have always seen obesity as a modifiable risk factor for many chronic diseases and some types of cancer and believed that reducing weight would reduce the risk of obesity-related comorbidities and healthcare expenditure. However, other observed and unobserved characteristics of the patients may interfere with their risk of developing obesity-related comorbidities and/or their ability to access healthcare services. Therefore, it is important to expand our understanding of the different dimensions of obesity. This thesis examined the phenomena of obesity from three different angles – the relationship between obesity and its comorbidities, accessibility to weight reduction (bariatric) surgeries and post-bariatric contouring surgeries, and cost-effectiveness analysis of a novel obesity treatment.Chapter 2 examined the impact of obesity on specific comorbidities including type 2 diabetes, hypertension, and vitamin D deficiency. Utilizing data from Saudi Arabia, two studies were conducted. In the first study, a series of biprobit regression analysis were used to explore unobserved heterogeneity across the obesity-related comorbidities. Unobserved heterogeneity was evident in the relationship between type 2 diabetes and hypertension. However, vitamin D was not found to predict type 2 diabetes risk nor hypertension risk.While the use of categorical dependent variables in the first study may not display the whole picture of the relationship between vitamin D and other obesity-related comorbidities, a second study was undertaken in chapter 2 with the aim to explore unobserved heterogeneity among subpopulations whose 25(OH)D level vary without recourse to an exogenously defined threshold. Using a relatively uncommon analysis known as the Finite Mixture Models, latent population subgroups and their relationship between vitamin D levels and sources of vitamin D were examined. Three latent classes were identified and their distinct patterns of associations with nutrition, behaviour and socio-demographic variables were presented.Weight reduction is a widely accepted intervention to prevent/delay the incidence of obesity-related comorbidities. However, access to weight reduction surgeries continues to be a challenge for ethnic minorities and socioeconomically disadvantaged groups. Ethnic minority groups such as Native Americans have a higher risk of developing obesity-related comorbidities. The small number of Native Americans in surveys makes it more challenging to investigate comparative ethnic group experiences. Nevertheless, the lack of research with respect to this group gives rise to a clear gap in our understanding regarding their comparative experience. Thus, the first study in chapter 3 examined disparities in access to bariatric surgeries with a particular focus on the experience of Native Americans utilizing one the largest dataset in the USA. Compared to White Americans, Native Americans were less likely to receive bariatric surgeries even when controlled for their clinical needs.The increasing popularity of bariatric surgeries as an impact of the insurance coverage expansion in 2011 have led to increasing demand for post-bariatric contouring surgeries. As rapid weight reduction can cause sagging skin, contouring (constructive or cosmetic) surgeries are seen as the best solution by most of those who have had bariatric surgeries in the past. However, not all types of contouring surgeries are covered by healthcare insurance. In fact, different insurance companies have their eligibility criteria for the covered procedures. The second study in chapter 3 examined the relationship between the use of contouring procedures on post-bariatric surgery patients, clinical need, and sociodemographic factors. Self-payers were more likely to receive post-bariatric contouring surgeries, which indicates that access could be predicted by the ability to pay rather than clinical need.Aside from invasive, costly surgeries, new less invasive procedures such as Aspiration therapy and gastric balloon have been introduced as competitors to bariatric surgeries. However, the decision-maker would not adopt a new procedure unless it have been assessed in terms of its cost-effectiveness and ensured that the cost-effectiveness analysis was unbiased. Chapter 4 examined the replicability of a published cost-effectiveness model comparing the Aspiration therapy with the bariatric surgeries. Two different reporting checklists were used. Both checklists show weak points in the paper, particularly in the parameter inputs. After updating the model’s input parameters, the model was used to explore the cost-effectiveness of gastric balloon therapy. Overall, this thesis demonstrates a number of economic aspects of obesity including: i) obesity is a modifiable risk factor for costly chronic diseases and subsequent cost saving is associated with weight reduction; ii) failure of the health insurance system in the USA to meet patients’ needs; and iii) adoption of rigor reporting checklist would improve the quality of published economic evaluations.
Date of AwardDec 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsSaudi Arabia Ministry of Health
SupervisorCiaran O'Neill (Supervisor) & Michael Donnelly (Supervisor)


  • Obesity
  • ethnic groups
  • bariatric surgery
  • insurance
  • American Indian
  • health economics
  • health expenditure
  • hypertension
  • diabetes
  • metabolic syndrome
  • dietary supplements
  • sedentary behaviour
  • finite mixture model

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