Date of Award


Degree Name

Master of Medicine / Surgery (Thesis)

Schools and Centres


First Supervisor

Professor Reginal V Lord

Second Supervisor

Dr Michael Swarbrick



Obesity is a polymorphic chronic disease that has reached epidemic proportions. Bariatric surgery including sleeve gastrectomy (SG) has an increasingly important role in long-term management of these patients. The molecular mechanisms post SG are complex and not fully understood.


The primary study aim is to investigate the hormonal mechanisms by which SG effects weight loss and related health benefits by examining the association between SG weight loss and biochemical/hormone levels. A secondary aim was to assess the improvements in obesity related chronic disease states following SG.


We conducted a prospective cohort study of obese patients undergoing SG and 2:1 age and sex matched non obese controls undergoing non- bariatric procedures during the study period from a single bariatric surgeon in Sydney. Height, weight, body mass index (BMI) and percentage excess body weight (%EBW) were determined for each subject at baseline, 3 and 6 months post SG.

Plasma samples were obtained and key biochemical markers measured (NEFA (non-essential fatty acids), C-peptide, Ghrelin, GIP (Gastric Inhibitory Peptide), Glucagon Like Peptide -1 (GLP-1), insulin, resistin, visfatin, glucagon, leptin, Plasminogen Activator Inhibitor-1 (PAI-1)). Comparisons of baseline levels between obese and non obese subjects; and pre and post surgery levels and clinical factors in the SG cohort at 0, 3, 6 months post SG were performed using unpaired and paired t-tests respectively on Graph-Pad PRISM © software


16 SG patients and 32 controls were included with 3 month clinical follow up available for all SG subjects and 3 month biochemical follow-up available for 11 SG subjects. In the SG cohort, the mean BMI at baseline was 43.5 +/- 1.8 kg/m2 SEM. Males undergoing SG were heavier than females. The mean %EBW loss was 42.3% +/- 8.4SD at 3 months and 51.5% +/- 18.5SD at 6 months. There was a statistically significant incremental weight loss between 3 and 6 month time points from baseline, p < 0.0001 and p < 0.0009 respectively.

A statistically significant decrease in levels of NEFA, ghrelin, GLP-1, glucagon, leptin and PAI-1 was observed between baseline and 3 months post-operative (p < 0.05). This reduction remained statistically significant at 6 months for NEFA and ghrelin. Due to small numbers at 6 months it is unclear if there are further changes in these hormone levels compared to 3 months.

No statistically significant difference was found for C-peptide, GIP, insulin or resistin between baseline and 3 months. Mean visfatin and resistin levels differed between subjects and controls at baseline (time 0). There was no difference in mean baseline BMI and %EBW lost for the patients who completed clinical and biochemical follow up versus those who had clinical follow-up alone.

In the SG cohort, secondary co-morbidities improved, with patients less dependent on oral hypoglycaemic agents for T2DM and improvements in hypertension, gastro-esophageal reflux disease and obstructive sleep apnea.


We demonstrate significant weight loss and hormone changes post SG surgery. Our research adds to the literature to identify markers that are associated with surgical weight loss that may provide insights into the endocrine mechanisms or effects of surgical weight loss.