Main Findings
Results show that under the current NICE guidelines for obesity, an estimated 3,623,505 or 7.78% (95% CL 7.07–8.58) of the population could potentially be eligible for bariatric surgery compared with 2,717,861 or 5.84% of the population under the previous guidance (95% CL 5.21–5.54). These numbers assume that those in the BMI 35–40 category have attempted weight loss already through non-surgical means as required by the NICE guidelines [
5]. Although it was not possible to ascertain who in that category had undertaken non-surgical interventions, it is unlikely that many had. However, evaluations of current medical and life style–focused weight loss programmes show that weight loss that is sustained by these programmes is often small, although significant [
14]. This means that it would be reasonable to assume that most of those that are eligible would remain eligible even after attempting non-surgical interventions. Certainly, not everyone who is eligible for bariatric surgery should necessarily be operated on. However, as the total number of bariatric surgeries performed in the UK in 2014 was 6032 [
7], there is a large difference between potential treatment demand and the availability of bariatric surgery. This penetration rate of 0.002% is particularly low compared with other published penetration rates, for example, 1.24% in the USA (where the eligible population was defined as adults with BMI ≥ 40) [
15] and 0.54% in Canada in 2017 (where the eligible population was defined as adults with BMI ≥ 35) [
16].
Results also showed that although a higher proportion of those eligible for surgery are female (~ 58% vs 42%), the proportion of females who received surgery is significantly higher (~ 76% vs 24%). There was also a significant difference in the age groups, with the eligible population being skewed towards older age groups and those that receive surgery being skewed towards younger age groups.
There does not appear to be a previous attempt to compare the UK eligible population with hospital episode statistics data. The closest previous study, published in 2014 (but using 2006 data), produced a similar model for estimating who was eligible using the previous NICE guidelines [
6]. Their results showed a similar pattern for demographics, although there was a higher proportion eligible in the younger age groups (18–24) and lower in the older age groups (65+) than in this study. The overall estimate for eligible population from that study was 5.1%, which compares closely with this study’s results using the previous guidelines (5.8%), and may partly be explained by considering the increases in obesity prevalence over the intervening eight years.
Limitations of this Study
The most important strengths and limitations come from the use of the Health Survey for England. This data source is a large, nationally representative sample with trustworthy data including measured heights and weights, and nurse visits to identify, for example—the medication that participants are taking. However, the routine nature of the data collection, rather than a bespoke design specific to our research question means that some variables, we would have ideally had access to, were unavailable. In addition, some conditions were only self-reported, meaning the prevalence of some comorbidities may be underestimated if they are undiagnosed.
Importantly, in terms of variables that were missing, there were several relevant conditions that might indicate surgery would be appropriate that were considered when planning this study, including obstructive sleep apnoea and polycystic ovary syndrome (additional to the comorbidities we did examine: type 2 diabetes, hypertension, osteoarthritis, cardiovascular disease, stroke, and hypercholesterolaemia). However, it was not possible to obtain information on the presence of these conditions from the Health Survey for England. The prevalence of some of the comorbidities chosen may have been underestimated, for example hyperlipidaemia could only be determined from those already taking lipid-lowering medications as there was not enough information to also include those that were untreated but with a raised serum cholesterol. Similarly, it was also difficult to distinguish between type 1 and type 2 diabetes. The Health Survey for England data used a distinction of type 1 being “diagnosed before age 35, treated with insulin” and type 2 being “diagnosed after age 35, not treated with insulin”. This could potentially underestimate the number with type 2 diabetes; however, it was the best way to distinguish between the two conditions with the data available.
The NICE guidelines recommend an assessment for bariatric surgery for those with a BMI of 30–34.9 kg/m
2 with recent-onset type two diabetes; however, there was not a way to determine which of the cases of type 2 diabetes was recent-onset so again, it is assumed that all those that had type 2 diabetes were eligible. This may overestimate the number eligible through this criterion, although the total number of type 2 diabetes cases is believed to be higher than estimated in this study. This study found the estimated prevalence of diabetes of any type to be 6.1%, whereas diabetes UK figures, based on the QOF data, reported the prevalence of all types of diabetes in England to be around 6.2% in 2014 [
17] and Public Health England estimated the number to be around 8.6% [
18], with 90% being type 2 diabetes (i.e. 7.7%).
Another possible source of error is a lack of detail in the NICE guidelines. This is presumably to allow for clinical judgement but it presented some difficulties when planning this study. An example of this would be a definitive BMI range for patients from an Asian background, with the guidelines giving the recommendation to consider surgery at a lower BMI range [
2,
12]. Another issue was which comorbidities to include, as a definitive list is not provided in the guidelines. There was also a lack of detail at which age surgery would usually be considered. The guidelines do not give an exact lower age, only recommending that surgery not be considered in “children and young people”. In the original study design, eighteen was chosen as a lower limit; however, when reviewing the hospital episode statistics data for 2014/2015, it was decided that this should be lowered to 16 to allow for an accurate comparison, as the lowest age range in the data was 16–24 [
7]. There is no stated upper age limit for surgery eligibility, as decisions should be made on a case-by-case basis.
Implications of this Study
Possible reasons for low demand for bariatric surgery among the eligible population include weight bias, which is high in the UK [
19]. Where obesity is attributed to personal irresponsibility, demand, and referrals for bariatric surgery may well be lower. Recent calls from the UK’s Royal College of Physicians [
20] to consider obesity a disease might counter any reluctance to encourage bariatric surgery in those patients who would benefit.
Other than the lack of bariatric surgery performed in comparison to demand, the main discussion points from this study would be to determine why there is such a difference in the sociodemographic proportions of who is eligible for surgery and who receives it. The difference in age groups may be due to older age groups being poor candidates for surgery or just an attempt at earlier intervention to prevent chronic comorbidities developing.
With regard to male and female populations, there may be a difference in the proportion seeking medical attention for weight-related issues, as well as concordance with guidance and treatment plans. It is already known that males are less likely to visit health care professionals due to different attitudes towards health care [
21]; however, it is not known whether this relates to obesity-related conditions. A previous study in California found that males who presented for bariatric surgery were typically older and with more severe comorbidities [
22], showing a greater need for earlier intervention in this group and greater potential benefit from receiving surgery. An area for follow up would be to speak to health care professionals, both in primary care settings to see who seeks help for obesity-related health problems and in secondary care to see who is referred and how surgical candidates are identified. This would help explain why there is such a difference and address any potential barriers to treatment.
Further follow-up work could be undertaken to see if there is a difference between eligibility and treatment in different ethnic groups, different socioeconomic classes, or an urban rural gradient. This would be dependent on the availability of data relating to these groups and bariatric surgery.