Bariatric surgery is becoming a more widespread treatment for obesity. Comprehensive evidence of the long-term effects of contemporary surgery on a broad range of clinical outcomes in large populations treated in routine clinical practice is lacking. The objective of this study was to measure the association between bariatric surgery, weight, body mass index, and obesity-related co-morbidities.
Methods and Findings
This was an observational retrospective cohort study using data from the United Kingdom Clinical Practice Research Datalink. All 3,882 patients registered in the database and with bariatric surgery on or before 31 December 2014 were included and matched by propensity score to 3,882 obese patients without surgery. The main outcome measures were change in weight and body mass index over 4 y; incident diagnoses of type 2 diabetes mellitus (T2DM), hypertension, angina, myocardial infarction (MI), stroke, fractures, obstructive sleep apnoea, and cancer; mortality; and resolution of hypertension and T2DM. Weight measures were available for 3,847 patients between 1 and 4 mo, 2,884 patients between 5 and 12 mo, and 2,258 patients between 13 and 48 mo post-procedure. Bariatric surgery patients exhibited rapid weight loss for the first four postoperative months, at a rate of 4.98 kg/mo (95% CI 4.88–5.08). Slower weight loss was sustained to the end of 4 y. Gastric bypass (6.56 kg/mo) and sleeve gastrectomy (6.29 kg/mo) were associated with greater initial weight reduction than gastric banding (2.77 kg/mo). Protective hazard ratios (HRs) were detected for bariatric surgery for incident T2DM, 0.68 (95% CI 0.55–0.83); hypertension, 0.35 (95% CI 0.27–0.45); angina, 0.59 (95% CI 0.40–0.87);MI, 0.28 (95% CI 0.10–0.74); and obstructive sleep apnoea, 0.55 (95% CI 0.40–0.87). Strong associations were found between bariatric surgery and the resolution of T2DM, with a HR of 9.29 (95% CI 6.84–12.62), and between bariatric surgery and the resolution of hypertension, with a HR of 5.64 (95% CI 2.65–11.99). No association was detected between bariatric surgery and fractures, cancer, or stroke. Effect estimates for mortality found no protective association with bariatric surgery overall, with a HR of 0.97 (95% CI 0.66–1.43). The data used were recorded for the management of patients in primary care and may be subject to inaccuracy, which would tend to lead to underestimates of true relative effect sizes.
Bariatric surgery as delivered in the UK healthcare system is associated with dramatic weight loss, sustained at least 4 y after surgery. This weight loss is accompanied by substantial improvements in pre-existing T2DM and hypertension, as well as a reduced risk of incident T2DM, hypertension, angina, MI, and obstructive sleep apnoea. Widening the availability of bariatric surgery could lead to substantial health benefits for many people who are morbidly obese.
In a UK cohort study, Ian Douglas and colleagues investigate weight, BMI, and related health outcomes after bariatric surgery.
Obesity—having an unhealthy amount of body fat—is a growing threat to global public health. Worldwide, 13% of adults are obese, and, in the UK and the US, the statistics are even worse. A quarter and a third, respectively, of adults in these countries are obese. Obesity is defined as having a body mass index (BMI; an indicator of body fat calculated by dividing a person’s weight in kilograms by their height in meters squared) of ≥30 kg/m2. Compared to people with a healthy weight (a BMI of 18.5–24.9 kg/m2), overweight and obese people have an increased risk of developing type 2 diabetes, cardiovascular conditions such as hypertension (high blood pressure), myocardial infarction (heart attack), angina, and stroke, and they tend to die younger. People become overweight, and eventually obese, by consuming food and drink that contain more energy (calories) than they need for their daily activities. So, obesity can be prevented and reversed by eating less and exercising more.
Why Was This Study Done?
People with severe obesity (BMI of 40 kg/m2 or more) who have tried but failed to control their weight through lifestyle changes sometimes undergo bariatric surgery (weight loss surgery). In the UK and the US, this approach is also recommended for obese individuals who have an obesity-related illness such as type 2 diabetes with a lower BMI of 35 kg/m2 or more. Techniques such as gastric band surgery, gastric bypass, and sleeve gastrectomy all lead to reduced energy intake, and in randomized controlled trials comparing bariatric surgery and lifestyle interventions, bariatric surgery is associated with greater weight loss. However, the results of clinical trials are not always replicated in routine clinical practice. Here, the researchers investigate whether there is an association between bariatric surgery and weight, BMI, and obesity-related co-morbidities (illnesses) in the UK by undertaking a retrospective cohort study (an observational study that compares recorded clinical outcomes in non-randomized groups of patients who received different treatments).
What Did the Researchers Do and Find?
The researchers used the UK Clinical Practice Research Datalink, which contains anonymized clinical information about patients provided by general practitioners (primary care physicians), to identify 3,882 patients who had had bariatric surgery. They matched each patient (average BMI 44.7 kg/m2), according to the patient’s medications and constellation of risk factors, to an obese individual from the dataset who had not had bariatric surgery. This “propensity matching” technique is used in studies where patients are not allocated at random to receive a treatment, and is meant to control for confounding—the possibility that patients who receive the treatment may be otherwise distinct from patients who do not. According to this analysis, patients who had had bariatric surgery lost weight rapidly during the first four post-operative months (4.98 kg/month); their weight loss was sustained at a slower rate for up to four years. By contrast, there were no weight changes in the patients who did not have surgery. Notably, bariatric surgery was associated with a lower risk of type 2 diabetes onset, hypertension onset, angina onset, myocardial infarction, and obstructive sleep apnea (a sleep disorder) onset, and with the resolution of both type 2 diabetes and hypertension in those who already had these conditions when they underwent surgery. However, over an average of 3.4 years of follow-up, there was no evidence of any difference in the risk of death.
What Do These Findings Mean?
These findings show that bariatric surgery delivered in routine clinical practice in the UK is associated with a substantial initial weight loss that is sustained for at least four years after surgery. They also show that bariatric surgery is associated with improvements in pre-existing type 2 diabetes and hypertension and with a reduced risk of developing several obesity-related co-morbidities. Because the data used in the study were recorded for patient management by primary care physicians, the researchers were unable to use strict diagnostic criteria for some outcomes, which may limit the accuracy of these findings. Nevertheless, these results suggest that widening the availability of bariatric surgery in the UK could provide substantial health benefits for many people who are morbidly obese. Indeed, the researchers calculate that, if the associations seen in this study are causal (an observational study cannot prove that a treatment causes a specific outcome), bariatric surgery could prevent and/or resolve many tens of thousands of cases of hypertension and type 2 diabetes and prevent similar numbers of cases of other obesity-related illnesses among the 1.4 million morbidly obese people living in the UK.
This list of resources contains links that can be accessed when viewing the PDF on a device or via the online version of the article at http://dx.doi.org/10.1371/journal.pmed.1001925.
The World Health Organization provides information on obesity (in several languages)
The Institute for Health Metrics and Evaluation website provides the latest details about global obesity trends; the World Obesity Federation also provides information about the global obesity epidemic
The UK National Health Service Choices website provides information about obesity (including some real stories), bariatric surgery (including some comments from patients), and healthy eating
The US Centers for Disease Control and Prevention has information on all aspects of overweight and obesity
ChooseMyPlate.gov is a resource provided by the US Department of Agriculture that provides individuals and healthcare professionals with user-friendly information on nutrition and physical exercise
The US National Institute of Diabetes and Digestive and Kidney Diseases provides information on bariatric surgery and on weight control and healthy living
MedlinePlus provides links to other sources of information on obesity and bariatric surgery (in English and Spanish)