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Surgery for Diabetes
Dr Asheesh Mehta Internal Medicine Specialist January 11, 2018
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Diabetes is an epidemic problem in many parts of the world including the Gulf region. The prevalence of diabetes is increasing in most countries. The WHO estimates that from a global prevalence of about 4.7% in adults over 18 years of age  in 1980, the prevalence had increased to 8.5% in 2014 and is now increasing even more. In absolute terms, there were about 108 million diabetics worldwide in 1980 while in 2014 their number was estimated to have gone up steeply to 422 million. Diabetes occurs due to an absolute or relative lack of insulin, the hormone produced by specialized cells located in the pancreas. Lack of insulin interferes with utilization of glucose by cells and results in an elevation in blood glucose levels. The two major types of diabetes are type-1 and type-2. In type-1 diabetes the pancreas does not secrete any significant amount of insulin. People with this type of diabetes need exogenous insulin to be administered, the usual route being by injection, for them to survive. In type-2 diabetes insulin secretion is deficient rather than absent and a resistance to the action of insulin at the cellular level is often present. This is much the commoner type of diabetes. Type-2 diabetes often responds to drugs that stimulate the pancreas to produce more insulin or those that facilitate the action of whatever insulin is being produced by the pancreas. More severe cases of type-2 diabetes also require exogenous insulin which is often used along with oral anti-diabetic drugs.

Type-1 diabetes is widely regarded as an auto-immune disease in which our own immune system attacks the insulin producing cells of the pancreas while in type-2 diabetes a number of factors including racial and genetic predisposition, obesity, lack of exercise, increasing age and stress are implicated. Central obesity in which fat collection is predominant in the abdomen has a higher risk than generalized obesity in which excess fat is deposited more or less proportionately all over the body. Much of the increase in prevalence of diabetes to pandemic levels is credited to lifestyle changes affecting diet, obesity and lack of physical exercise. Adoption of a healthier lifestyle with more fruits and vegetables in diet, avoiding simple sugars and excessive intake of all carbohydrates, reduction of weight and regular physical exercise reduce or delay the development of diabetes even in people with significant genetic risk for this disease. Unfortunately, obesity continues to be rampant and a large proportion of such individuals are not able to make much headway in achieving sustained weight loss. Bariatric surgery which is the technical term for weight loss surgery is an effective option in treating gross obesity. An incidental benefit which was first noted as long back as the 1980s was that the type-2 diabetes which many of these individuals suffered went into remission after weight loss surgery. This was a highly gratifying result since all other treatments only control diabetes - they are not able to achieve a remission. Considering these results, bariatric surgery has gradually been adopted as an option in management of type-2 diabetes. It has no role to play in treatment of type-1 diabetes.

There is a favourable response in diabetes control after all types of weight loss surgery. However, best results are seen after the surgeries which result in greater weight loss

Most of the time, bariatric surgery is done in people with significant obesity and if the person has diabetes it serves as an added inducement for this type of surgery. The usually recommended cut-off level for qualifying for bariatric surgery as a means to treat diabetes is a BMI of 35 or above. BMI is the acronym for Body Mass Index and is derived by dividing the weight in Kg by the square of the height in metres (Weight / Height²). BMI is the most widely adopted measure of obesity. Desirable or normal BMI is between 18.5 to 24.9. A BMI between 25 and 29.9 classifies the individual as overweight while a BMI above 30 denotes obesity. The BMI suffers from a few problems such as diagnosing overweight in excessively muscular individuals and underestimating abdominal obesity, the far more problematic type of obesity. In spite of these limitations it remains a very useful indicator of obesity and underweight in most individuals. While a diabetic with a high BMI is likely to benefit most from bariatric surgery it has been found that the surgery is also effective in achieving a diabetes remission even when there is no  significant obesity. In other words the favourable effect of bariatric surgery on diabetes is not by weight loss alone. This supposition is further strengthened by the finding that diabetes remission is usually noted within a few days to weeks of the surgery, well before substantial weight loss has been achieved. How this is achieved is not too clear. One possible mechanism is bypassing a short segment of the proximal small intestine which results in altered signals affecting blood glucose control. Another theory is that delivery of nutrients to the distal small intestine because of the bypass is the source of signals resulting in favourable blood glucose control.

There is a favourable response in diabetes control after all types of weight loss surgery. However, best results are seen after the surgeries which result in greater weight loss. Duodenal switch surgery is generally carried out for the most obese individuals. About 70% of the stomach is removed and passage of food is rerouted so that a large length of the small intestine is bypassed. This results in restriction of food intake as well as interference with absorption of food. This surgery achieves very significant weight loss in most individuals and also the best results of diabetes remission in more than 90% of cases. Gastric bypass is a less radical surgery and achieves somewhat lower, although still very satisfactory, weight loss as compared to duodenal switch. After gastric bypass surgery, food bypasses most of the stomach and the upper part of the small intestine. About 80% of diabetic patients undergoing this surgery achieve a remission of diabetes and another 15% show significant improvement in control of diabetes. Also, when nondiabetic individuals with obesity undergoing gastric bypass surgery (or other bariatric surgery) are followed up, much lesser number of them develop diabetes as compared to matched controls. Sleeve gastrectomy is another type of weight loss surgery in which part of the stomach is removed. This surgery is usually recommended for relatively less obese individuals. The surgery is also effective in inducing diabetes remission independently of weight loss. Diabetes remission is achieved in about 60% of type-2 diabetics undergoing this surgery. Adjustable gastric band involves placement of a band around the upper part of the stomach which helps in restricting food intake and thus achieving weight loss. Gastric banding is carried out in less obese individuals with the aim of achieving moderate weight loss. The results of diabetes remission are correspondingly lower at around 45%.

While bariatric surgery does achieve excellent results in obese diabetics, the negative aspects also need to be highlighted. All surgery has an inherent risk and this is also true of bariatric surgery. The operative risk is further increased in such patients because of the underlying problems of obesity and diabetes. The team carrying out the surgery will surely take all due precautions to reduce risk by carrying out required investigations and adopting rectification measures prior to and during surgery but even in the best of hands there is a small risk which can never be claimed to be negligible or irrelevant. Further, there are also potential complications associated with the various bariatric surgeries. These are commonest after the more aggressive types such as duodenal switch and gastric bypass. Direct surgical risks include perforation of stomach or intestine, leakage at suture site, infection and post-operative adhesions causing intestinal obstruction. Malabsorption of food and deficiencies of nutrients such as vitamins and minerals is quite common after duodenal switch and is also an issue with gastric bypass and other bariatric surgery but to a lesser extent. Lifelong monitoring to detect and treat such deficiencies and also supplementation with vitamin and mineral preparations is indicated. There is also a risk for development of gall stones after all bariatric surgery and many surgeons carry out removal of the gall bladder at the time of the bariatric surgery itself to circumvent this potential complication.

In spite of the potential risks of complications of bariatric surgery it remains a very viable option in properly selected diabetics. Bariatric surgery is currently recommended for obese diabetics with a BMI of 35 and above. Diabetics with BMI of between 30 and 35 may also be advised weight loss surgery if diabetes is not controllable in spite of best efforts. This recommendation is further strengthened when these patients suffer significant associated medical problems such as heart disease. In diabetics with a BMI below 30, even though this type of surgery will often achieve a remission, it is not generally advised. In any case bariatric surgery is useful only in type-2 diabetes and is not recommended for type-1 diabetes patients.

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