Friday August 28 2009
Weight-loss surgery is not the solution to diabetes
The Times and other newspapers have reported on a large international study finding that “weight-loss surgery can eliminate the symptoms of type 2 diabetes in nearly eight out of 10 patients”. See The Times' story on the effects of weight-loss surgery on diabetes.
The news stories are based on a thorough and well-conducted review of the effect of bariatric (weight-loss) surgery on weight and type 2 diabetes. Studies with a total of 4,070 diabetic patients found bariatric surgery to be greatly effective for both reducing weight and improving diabetes, both in the short and long term. There are some limitations to the research, including the fact that it combined studies that used very different methods.
The principal point is that the findings must be interpreted in the right context. Bariatric surgery may be expected to lead to some improvement in diabetes because it causes weight loss, but this does not mean that weight-loss surgery is the solution to diabetes.
Bariatric surgery is only ever performed as a last resort in morbidly obese people who meet strict criteria, have failed in other attempts at weight loss, have other weight-associated diseases and consent to intensive long-term management in a specialist obesity service.
Where did the story come from?
The research was carried out by Dr Henry Buchwald and colleagues from the University of Minnesota and other US institutions. The study was funded by Ethicon Endo-Surgery, Inc., a Johnson & Johnson Company, Ohio, US. The study was published in the peer-reviewed medical journal The American Journal of Medicine.
What kind of scientific study was this?
In this systematic review the researchers combined the results of studies in which people had bariatric (weight-loss) surgery, to see the effect it had on weight reduction and type 2 diabetes.
The researchers searched medical databases for all studies published in English from January 1 1990 to April 30 2006 on banding, gastroplasty, gastric bypass or biliopancreatic diversion/duodenal switch, and that had assessed weight loss and type 2 diabetes outcomes. All study designs were included and their findings combined using a statistical technique called meta-analysis.
The researchers pooled outcomes reflecting improvement in type 2 diabetes within two years of surgery, and longer-term improvement after two years. The studies measured improvement using insulin levels, glycated haemoglobin (HbA1c) tests and fasting glucose levels. The researchers also investigated the effect of type of surgery on diabetes and overall weight reduction.
All studies were assessed for quality. The researchers say that they performed sensitivity analyses based on the quality of the underlying studies, but only appear to report their overall analyses. Data on the studies, patients and treatments were summarised, and outcomes of weight loss and clinical and laboratory manifestations of diabetes were collected. Results were combined for each type of surgery and outcome of interest.
What were the results of the study?
The researchers found 621 studies that met their inclusion criteria. These covered 888 different treatment arms and 135,246 patients. When they looked only at studies that had reported on the resolution of clinical and laboratory manifestations of type 2 diabetes, they found 103 treatment arms involving 3,188 patients. In 19 studies, weight loss and diabetes resolution were reported separately for 4,070 diabetic people. Only 30 studies were randomised controlled trials and of these 10 were rated as class I evidence (a high-quality study).
The average age for people receiving bariatric surgery was 40.2 years. Women made up 80% of the total and the average BMI was 47.9. The review gives extensive results, and weight-loss results are reported separately for each type of surgery, but overall weight loss was 38.5kg or 55.9% loss of excess body weight.
There was complete diabetes resolution in 78.1% of patients, and diabetes was improved or resolved in 86.6% of patients. Of the different treatments, biliopancreatic diversion/duodenal switch gave the greatest improvement in weight reduction and diabetes resolution (95.1% resolved). This was followed by gastric bypass (80.3%). Banding procedures gave the lowest improvement (56.7% resolved).
There was a significant postoperative reduction in insulin levels, HbA1c and fasting glucose values. There was little difference between weight loss and diabetes within two years of surgery or longer term after two years.
What interpretations did the researchers draw from these results?
The reviewers conclude that the clinical and laboratory manifestations of type 2 diabetes are resolved or improved in the majority of patients who have bariatric surgery. Procedures associated with the greatest loss of excess body weight gave the most pronounced improvement.
What does the NHS Knowledge Service make of this study?
This systematic review and meta-analysis pooled the results of all identified studies that examined the effect of bariatric surgery on weight loss and type 2 diabetes. It found surgery to be effective for both, in the short and long term. There are some limitations to the research, which the authors acknowledge, including:
- the possibility of publication bias in the studies that have been included (those with less favourable results not being published),
- the variable reporting and measurement of study outcomes,
- high loss to follow-up of treated patients, and
- lack of specific information on subgroups, such as those of different ethnicity.
In addition to these, the review pooled studies with very different methodologies. Only a very small proportion of studies were of high quality and, although the researchers say they performed sensitivity analyses based on study quality (which suggests they must have pooled only these high-quality studies), they only report these for one outcome. The high-quality studies may give different findings that are more robust.
Given that type 2 diabetes is associated with obesity, high cholesterol and hypertension, it is not surprising that the large reduction in weight and dietary intake associated with bariatric surgery would result in significant improvement in diabetes.
However, these findings must be interpreted in the right context. This does not mean that weight-loss surgery is the solution to diabetes. Bariatric surgery is only ever performed as a last resort in morbidly obese people who fulfil the following strict criteria as defined by NICE:
- BMI of 40 or more, or between 35 and 40 and other significant disease (for example, type 2 diabetes or high blood pressure).
- When all appropriate non-surgical measures have been tried, but have failed to achieve or maintain adequate, clinically beneficial weight loss for at least six months.
- The person has been receiving or will receive intensive management in a specialist obesity service.
- The person is generally fit for anaesthesia and surgery.
- The person commits to the need for long-term follow-up.