A number of procedures for weight-loss surgery (termed 'bariatric surgery') have been developed which can work by reducing the functional size of the stomach ('restriction'), reducing the capacity of the gut to absorb calories ('malabsorption') or by a combination of the two. The well-documented improvement in diabetes following such surgery has puzzled doctors but the evidence suggests it is due in part to the altered transit of food through the gut. It is therefore possible that different procedures would give different degrees of improvement. This is what Associate Professor Markku Peltonen at the National Institute for Health and Welfare, Finland and colleagues from the University of Gothenburg, Sweden, set out to investigate using data from the large 'Swedish Obese Subjects' study.
2010 severely obese patients (with BMI>34 in men and >38 in women) recruited to the study went on to receive bariatric surgery: 376 gastric banding, 265 gastric bypass (GBP), and 1369 vertical banded gastroplasty (VBG -- see below for descriptions). They followed 74% of these patients at both 2 and 10 years and measured improvements in diabetes via blood glucose and insulin levels before and after surgery. The degree of weight loss was categorised as more than 30kg, 30-25kg, 25-20kg and 20-15kg. Improvements in blood glucose and insulin were then compared between the three different surgical procedures accounting for the degree of weight loss.
After 10 years, the researchers found there was no significant difference in the changes to insulin and glucose levels between the three surgical groups when the extent of their weight loss was taken into account. This was true for patients with and without diabetes at baseline. The average 10 year weight losses were 18kg, 20kg and 29kg for the banding, GBP and VBG groups respectively (p<0.001). In a further analysis patients that lost the same amount of weight improved their blood glucose and insulin levels to similar degrees, regardless of the type of surgery.
The researchers conclude that the remarkable improvements in diabetes following weight loss surgery are not a direct result of the procedure itself. More research now needs to take place to investigate why bariatric surgery can cure diabetes in these patients, and why some patients respond better than others.
Associate Professor Markku Peltonen, Director of Department at the National Institute for Health and Welfare, Finland, said:
"Bariatric surgery is clearly effective in reducing weight in patients, but the current mystery is why so many patients appear to cure themselves of diabetes shortly after the operation.
"We would expect that some methods of weight loss surgery would be more effective at treating diabetes than others due to the different ways they alter the passage of food through our gut. When we factored in the weight lost following surgery we found that no procedure was any better at treating diabetes than another.
"Perhaps it is simply the act of losing weight that helps."
Bariatric Surgery
Gastric banding reduces the functional size of the stomach by fitting a belt around the top section, so that it requires very little food to fill and therefore produces 'satiety' hormones after less food. The food is allowed to slowly pass into the main chamber of the stomach to continue digestion as normal. Adjustable gastric bands can be tightened or loosened to control this rate.
Gastric bypass surgery staples off the top portion of the stomach and creates a new route for food from this top portion to the small intestine, thus reducing the functional size of the stomach and bypassing much of the digestion and absorption that occurs in the stomach and small intestine. Bypassing more of the small intestine gives more rapid weight loss.
Vertical banded gastroplasty is a similar technique to gastric banding but is more complex.
Other techniques have been developed, although they are not covered as part of this study.
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