This study showed that almost half of the people attending the specialist T2DM clinic have a BMI ≥35 kg/m2 and meet the criteria for bariatric surgery, and less than a quarter achieve an HbA1c < 53 mmol/mol (7%). However, only 1 in 5 of the people that met the criteria were offered a referral to an obesity/metabolic clinic or for bariatric surgery. This audit also showed that the BMI≥35kg/m2 group were younger but already had diabetes for an average of 11 years, had higher insulin requirements and were more likely to have additional medications or doses added to their regimen during consultation. They had a similar diabetes duration to the BMI < 35 kg/m2 group, with no difference in initial HbA1c.
The high proportion of people with BMI ≥35 kg/m2 in our clinic aligns with an audit of a specialist diabetes clinic in the UK, which revealed that 52% of participants with T2DM had obesity (BMI≥30kg/m2) and a further 8.1% had a BMI≥40kg/m2 [21]. The people with obesity were younger, had worse glycaemic control, higher blood pressures, and were more likely to be on an antihypertensive or lipid lowering medication compared to the people with a BMI < 30 kg/m2 [21]. Although there is a paucity of studies which have assessed obesity in T2DM clinics, our results and those of the study from the UK show that in people with T2DM, obesity is extremely common and associated with worse outcomes. The low proportion of referrals for surgery or obesity/metabolic clinics in our study can be attributed to a combination of lack of publicly funded obesity services and availability of bariatric surgery [20][22]. Barriers to accessing obesity/metabolic clinics in Australia have been detailed previously by Atlantis et al. and include factors such as strict entry criteria (eg. BMI≥40kg/m2), prolonged wait times, and out-of-pocket costs [22]. Furthermore, the sixth annual report from the Bariatric Service Registry of Australia stated that in 2019, only 6.1% of primary bariatric surgeries were publicly funded, the rest being privately funded [19]. Previous studies have shown that there is also a reluctance in both patients and health care professionals to opt for bariatric surgery due to bias, negative media and attitudes towards weight-loss surgery [23][24].
Data from the UK’s National Diabetes Audit (NDA) showed little association between BMI and adverse outcomes, apart from an inverse gradient for stroke and MI. Similarly, in our study, the BMI≥35kg/m2 did not have a higher rate of microvascular or macrovascular complications compared to the BMI < 35 kg/m2 group [25], although the BMI≥35kg/m2group was younger. As expected, the prevalence of OSA was much higher in the BMI≥35kg/m2 group (26% vs 6.5%, p < 0.001) [26]. It is possible that many people in this diabetes clinic have undiagnosed OSA, given that previous studies have demonstrated much higher prevalence of OSA in a specialist diabetes outpatient population [26]. The BMI≥35kg/m2 group also had a higher prevalence of foot ulcers, thus aligning with a previous study which showed a positive correlation between obesity and diabetic foot ulcers [27].
A retrospective cohort study from Australia, consisting of people with T2DM and BMI≥30kg/m2, compared glycaemic control in participants attending a multidisciplinary weight management clinic to participants receiving “best practice” care in a specialist diabetes clinic [28]. At 30 months, the people attending the weight management clinic achieved a greater HbA1c reduction than those attending the diabetes clinic [28]. This suggests that our BMI≥35kg/m2 population, who had similar baseline characteristics to the participants in the cohort study, are more likely to achieve better glycaemic control by attending a weight management clinic. This may be because of the multidisciplinary nature of weight management programs that have greater dietitian and psychologist support, and the data here showing very few patients in the clinic were seen by a dietitian. Another study of a publicly funded metabolic clinic in Australia revealed that people with T2DM and a BMI≥40kg/m2 benefitted from improved glycaemic control and reduced diabetic medication load after 6 months of attending the clinic [29], significantly more so than the BMI≥35kg/m2 population in this study. Therefore, the BMI≥35kg/m2 group may have been better served in the multidisciplinary obesity service, leaving more capacity for the specialist diabetes clinic to see more patients with T2DM and its complications. This is further supported by the fact that new patients to the clinic saw an improvement in HbA1c in the first year, but there was no ongoing further improvement in glycaemia, although the initial benefit seemed to be maintained. Hence, there is also potential for these patients to be discharged back to primary care since they do not require long-term specialist follow-up. As a result, this would increase capacity in the already strained public T2DM clinic.
In the Look AHEAD trial, people with type 2 diabetes and overweight/obesity who received intensive lifestyle intervention for weight loss had a lower HbA1c, reduced sleep apnoea, reduced diabetes medication requirements, improved mobility and quality of life, fewer hospitalisations, and reduced healthcare costs [9]. With regards to bariatric surgery, a study of 5-year outcomes comparing bariatric surgery to medical therapy revealed that participants with type 2 diabetes who underwent surgery alongside medical therapy were far more likely to achieve the HbA1c < 6% target than those receiving medical therapy alone [30]. In addition, a post-hoc analysis of participants from the Swedish Obese Subjects Study revealed that bariatric surgery was associated with a reduced risk of microvascular complications in patients with diabetes [31]. Bariatric surgery data have also shown that diabetes duration is important in predicting who is likely to achieve diabetes remission [14]. The DiRECT trial also highlighted the importance of intervening soon after the diagnosis of T2DM for diabetes remission with weight loss. Thus, these studies suggest that the presence of obesity should be recognised early on in type 2 diabetes and managed alongside glycaemia, with timely referrals to obesity clinics or for bariatric surgery if appropriate, as significant sustained weight loss can improve glycaemic control, overall health, and lead to remission of diabetes.
The American Diabetes Association (ADA) guidelines recommend the use of weight lowering anti-diabetes medications in people with T2DM and obesity [32]. Weight loss in the setting of T2DM is imperative, with the DiRECT trial demonstrating, in a UK primary care setting, that significant sustained weight loss in participants with recently diagnosed diabetes resulted in almost half of the participants achieving diabetes remission at 12 months [10]. In our BMI≥35kg/m2 group, use of weight-lowering medications was limited with less than 1 in 5 participants on a GLP1 agonist and only a quarter on an SGLT2 inhibitor. Data from the Australian National Diabetes Audit (ANDA) showed that in 2019, 27% of people with T2DM were on an SGLT2 inhibitor and 12% were on a GLP1 receptor agonist [33]. Although our use of weight lowering medications in the BMI≥35kg/m2 group was comparable to that of the ANDA, the figures in our specialist clinic should have been higher as the mean BMI of the ANDA population was only 33.5 kg/m2 [33]. However, some of these agents like GLP1 agonists and SGLT2 inhibitors are relatively new and are more expensive than the traditional therapies including sulphonylureas and insulin, which treating clinicians may be more familiar with. Unlike the weight-lowering agents, sulphonylureas are associated with weight gain [31]. In our BMI≥35kg/m2 group, sulphonylurea use was appropriately lower than in the BMI < 35 kg/m2 group.
This study has some limitations. This is a single centre study of a publicly funded specialist diabetes clinic. However, there are several endocrinologists practising within this clinic. A proportion of people were excluded from the study as their records did not contain a height or weight. There was also a lack of serial weight measurements for the majority of patients which may indicate that staff in the specialist clinic were more focussed on glycaemic control rather than obesity management. Furthermore, some people only attended the clinic once, which made it difficult to assess their progress in regards to weight loss and glycaemic control. The retrospective study design does not account for discussions regarding bariatric surgery or referral to a metabolic clinic which were not documented. A major strength of this study is that all eligible people who attended the clinic were included in the study.