An estimated 1.7 billion people worldwide are overweight or obese, according to an article outlining the findings of the data analysis in the October 13 Journal of the American Medical Association.

Overweight is defined as having a body mass index (BMI) of 25 or higher; obesity is defined as a BMI of 30 or higher; and morbid obesity as 40 or higher.

Being obese is associated with a greater risk for type 2 diabetes, hypertension, heart disease, stroke and asthma. The loss of life expectancy due to morbid obesity is significant: A 25-year-old morbidly obese man has a 22 percent reduction in expected remaining lifespan, compared to a normal-weight individual. That represents a loss of approximately 12 years of life.

For treating obesity long term, diet therapy has been found to be relatively ineffective, the article notes.

A team led by Henry Buchwald, M.D., Ph.D., of the University of Minnesota, Minneapolis, reviewed 136 studies published between 1990 and 2003, which included 22,094 patients who underwent obesity surgery. The researchers wanted to determine the impact of the surgery on weight loss, operative mortality outcome, and four obesity related disorders (diabetes, hyperlipidemia, hypertension and obstructive sleep apnea).

The surgical procedures performed on patients in the studies included gastric banding, gastric bypass, gastroplasty, biliopancreatic diversion or duodenal (part of small intestine) switch, and others (such as jejunoileal bypass, a bypass of a section of the small intestine).

Nineteen percent of patients were men and 72.6 percent were women, with an average age of 39 years. The average body mass index for 16,944 patients was 46.9 before surgery.

The researchers found that the average percentage of excess weight loss was 61.2 percent for all patients; 47.5 percent for patients who underwent gastric banding; 61.6 percent, gastric bypass; 68.2 percent, gastroplasty; and 70.1 percent, biliopancreatic diversion or duodenal switch.

Death due to surgery within 30 days of the procedure was 0.1 percent for purely restrictive procedures (gastric banding and gastroplasty), 0.5 percent for gastric bypass, and 1.1 percent for biliopancreatic diversion or duodenal switch.

Diabetes was completely resolved in 76.8 percent and resolved or improved in 86 percent of patients. Hyperlipidemia (elevated levels of cholesterol and triglycerides in the blood) improved in 70 percent or more of patients. Hypertension was resolved in 61.7 percent, and resolved or improved in 78.5 percent of patients. Obstructive sleep apnea was resolved or improved in 83.6 percent of patients.

"Even after accounting for the pain and anxiety of surgery, the inconveniences of dietary restrictions, and possible complications including reoperation, quality of life should improve for the majority of bariatric surgery patients," say the researchers.

"A weight loss often in excess of 45 kg (approximately 100 lbs.), relief from fatal comorbid diseases, improved appearance, and improved social and economic opportunities should markedly enhance quality of life, and several studies support this contention," the research team concludes.