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Lap Band Gastric Bypass Surgery Improves Insulin Resistance

A new study examining the overall and gender-related effects of laparoscopic gastric banding surgery (LGBS) on insulin resistance, body composition, and metabolic risk markers six months post-surgery has found significant improvements in insulin resistance. The improvements occurred despite continuing obesity. Overweight and obesity have reached epidemic proportions in the United States. In fact, 65 percent of Americans are currently considered overweight or obese. Using body mass index (BMI) standards, overweight is defined as BMI between 25-30 kg/m2; obesity is defined as BMI>30 kg/m2.

Excess body fat is not simply a cosmetic problem; it constitutes a health risk as well. As the amount of adipose tissue (body fat) increases, the concentrations of substances produced in adipose tissue can become grossly abnormal. In addition, fat becomes deposited in the pancreas, liver and muscle, leading to metabolic derangements such as insulin resistance and/or diabetes. Obesity causes hypertension and abnormal levels of fat in the blood.

Because of the low success rate of calorie restriction (i.e., diets) in reducing morbid obesity, surgical intervention is increasingly common. Individuals are considered candidates for surgery if BMI>40 kg/m2, or if BMI is 35-40 kg/m2 with significant co-morbidities.

Gastric Bypass (RYGB) is the most commonly performed bariatric operation in the US, and often considered the “gold standard” by which other surgical procedures are judged. This procedure involves a rearrangement of the gastrointestinal (GI) architecture so that food bypasses about 95 percent of the stomach and large parts of the small intestine. In contrast, LGBS involves only a restriction on the stomach, so that less food can be ingested. In this procedure, an inflatable silicone band is placed around the top of the stomach in order to create a small stomach pouch. The band can be filled with varying volumes of saline so that the outlet from the small stomach pouch can vary in size. Thus, the speed of emptying food from the stomach can vary. With LGBS, there is no rearrangement of the gastrointestinal architecture and food that is ingested does not bypass any of the GI tract.

Many studies have shown that RYGB is very successful in controlling diabetes, even before substantial weight loss has occurred. Fewer studies investigating reductions in cardiovascular and metabolic risk factors after LGBS have been published. This study was undertaken to determine the overall and gender-related effects of LGBS on body composition, insulin resistance, and metabolic risk markers six months after LGBS.

Volunteers were recruited from a physician practice performing LGBS surgery. The intent was to follow patients for one year post-surgery. As of March 2007, 12 men and 17 women have been followed for six months post-surgery.

Before surgery, the team evaluated body composition using a variety of methods. Fasting blood samples were taken to evaluate metabolic risk biomarkers, including blood lipids, insulin, glucose, cardiac C-reactive protein (CRP), fatty acids, homocysteine, hemoglobin A1 (HbA1c), ApoA1, and ApoB. Resting blood pressure was also measured. Insulin resistance was estimated using a simple index (HOMA) that is based on fasting plasma insulin and glucose concentrations.

The researchers found the following: prior to surgery, there were expected gender differences in body composition measures. Men were heavier, had greater waist circumferences, L4L5 VAT, total VAT, and HbA1c. Women had higher a percentage of body fat.

Six months after surgery the overall group had a l5 percent reduction in body weight (275 vs. 233 pounds), a 14 percent reduction in BMI (43.4 vs. 37.3), a 13 percent reduction in body fat percentage (49 vs. 43 percent), a 13 percent reduction in waist circumference (53 vs. 46 inches) and a 10 percent reduction in hip circumference (57 vs. 51 inches). Total VAT was reduced by 20 percent (6.5 vs. 5.2 kg).

The insulin resistance was reduced 60 percent, according to a HOMA score. This was due primarily to a 50 percent reduction in fasting insulin concentrations with no change in fasting glucose concentrations.

There were a few gender differences in surgery-related changes. In women only, the waist-to-hip ratio tended to decrease (0.92 vs. 0.86), and the HbA1c tended to decrease (5.8 vs. 5.6 percent). In men only, total VAT was significantly reduced (8.7 vs. 6.6 kg). Diastolic blood pressured tended to decrease (81 vs. 75 mmHg) and CRP tended to decrease (8.3 vs. 4.7 mg/L).

Many studies have shown the benefit of RYGB surgery for improvement in insulin resistance in morbidly obese patients. This study demonstrates that there are also significant improvements in insulin resistance six months after LGBS. After six months, the largest and most significant changes in the group were variables suggestive of insulin resistance. These improvements occurred despite the fact that patients were still clinically obese. Rapid improvements in insulin resistance after surgery will have a positive impact on long-term patient health and may delay or prevent progression to diabetes.

Dr. Carroll presented the findings at the 120th annual meeting of the American Physiological Society (APS; http://www.The-APS.org)

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