Fourteen RCTs compared the weight-reducing effect of different surgical interventions. They did not compare surgery versus no intervention. Because of the nature of the intervention, there is a reluctance to do such a randomized trial.
Rationale: Of the 14 RCTs that examined the effect of surgical procedures on weight loss, 8 were deemed appropriate. All the studies included individuals who had a BMI of 40 kg/m2 or above, or a BMI of 35 to 40 kg/m2 with comorbidity; most of the study participants were women. Weight loss due to surgical intervention such as the gastric bypass ranged from 50 kg (110 lb) to as much as 100 kg (220 lb) over a period of 6 months to 1 year. Gastroplasty with diet had a favorable net outcome on weight loss after 2 years compared to diet alone (515). Vertical-banded gastroplasty was more effective than horizontal-banded gastroplasty (516). Gastric resection with a modest biliopancreatic diversion without intestinal exclusion resulted in significantly greater weight loss than conventional Roux-en Y gastric bypass; this long-limb modification of Roux-en Y gastric bypass was shown to be safe and effective in patients who were 200 lb or more overweight and did not cause additional metabolic sequelae or diarrhea (517).
The Swedish Obesity Study (SOS) (518), a non-RCT, found that gastric bypass produced greater weight loss than gastroplasty, 42.3 kg (93.3 lb) versus 29.9 kg (67 lb), at 1 year. The gastric bypass was deemed superior to gastroplasty or gastric partitioning in other RCTs as well (518-522). The SOS also evaluated the correlation between stoma size and weight loss in patients assigned to gastric bypass or gastroplasty, and found no significant correlation in the gastric bypass group.
Comorbidity factors associated with weight loss showed improvement after surgery. One study showed that medical illnesses either improved (47 percent) or resolved (43 percent) in all but four patients (9 percent), and these four had unsatisfactory weight loss (517). The Adelaide Study showed that 60 percent of the patients who initially had obesity-related comorbidity were free of medication for these comorbidities 3 years after surgery (519).
Extremely obese persons often do not benefit from the more conservative treatments for weight loss and weight maintenance. Obesity severely impairs quality of life, and these individuals are at higher risk for premature death (523). The National Institutes of Health Consensus Development Conference consensus statement, Gastrointestinal Surgery for Severe Obesity (523), concluded that the benefits outweigh the risks and that this more aggressive approach is reasonable in individuals who strongly desire substantial weight loss and have life-threatening comorbid conditions.
The effects of surgery on abdominal fat or cardiorespiratory fitness independent of weight loss are unknown. One small study demonstrated that surgery (adjustable silicone gastric banding) reduced abdominal visceral fat. No analyses were performed to examine whether visceral fat reduction was independent of weight loss (524). There are no data on the effects of surgery on changes in cardiorespiratory fitness.