Obesity has become a global epidemic, with over two-thirds of adults in Western and resource-rich countries classified as overweight or obese. It is the second-largest public health concern after smoking, contributing to numerous comorbidities such as type 2 diabetes, hypertension, obstructive sleep apnea, and certain cancers. Severe obesity reduces life expectancy by 5–20 years and significantly impacts quality of life. Despite advances in nonsurgical treatments, such as dieting, exercise, and lifestyle interventions, these approaches often result in short-term weight loss (6–8% of body weight) followed by weight regain. Pharmacotherapy has also proven ineffective in the long term. As a result, bariatric surgery has emerged as the most effective treatment for severe and complex obesity, offering sustained weight loss and improvement in obesity-related diseases.
Historical Evolution of Bariatric Surgery
The history of bariatric surgery dates back to the 1950s, when operations were first performed to treat severe hyperlipidemia and obesity. Early procedures, such as the ileocolic and jejunoileal bypass, were malabsorptive but associated with severe complications, including diarrhea, electrolyte imbalances, malnutrition, and liver failure. In 1969, Mason and Ito introduced the first gastric bypass, which was later modified to the Roux-en-Y gastric bypass (RYGB) to address bile reflux esophagitis. The 1980s saw the rise of the vertical banded gastroplasty (VBG), a restrictive procedure that became popular due to its initial success but fell out of favor due to long-term weight regain and complications.
The advent of laparoscopic techniques in the 1990s revolutionized bariatric surgery. The first laparoscopic adjustable gastric banding (LAGB) was performed in 1994, followed by laparoscopic RYGB the same year. LAGB gained popularity in Europe and Australia but was later overshadowed by the rapid adoption of sleeve gastrectomy (SG) as a primary bariatric procedure after 2008. Today, SG and RYGB are the most commonly performed bariatric surgeries worldwide.
Current State of Bariatric Surgery
Bariatric surgery has evolved significantly, with a shift in procedural preferences. Sleeve gastrectomy (SG) now accounts for 46% of all bariatric procedures globally, followed by RYGB (40%) and LAGB (7%). The laparoscopic approach has become the standard, reducing morbidity and mortality while improving patient outcomes. Additionally, bariatric surgery has expanded beyond weight loss to include metabolic surgery, particularly for treating type 2 diabetes (T2DM) in patients with less severe obesity. This shift is supported by robust evidence demonstrating the metabolic benefits of these procedures.
Mechanisms of Action
Bariatric procedures were traditionally classified as either restrictive (e.g., SG, LAGB) or malabsorptive (e.g., RYGB). However, research has revealed that the mechanisms of action are more complex and involve physiological changes beyond anatomy. Key mechanisms include:
- Hormonal Changes: Alterations in gut hormones such as glucagon-like peptide-1 (GLP-1), peptide YY (PYY), ghrelin, and leptin play a significant role in appetite regulation and glucose metabolism.
- Microbiome Modulation: Changes in gut microbiota composition contribute to metabolic improvements.
- Bile Acid Metabolism: Bile acids influence insulin sensitivity and energy homeostasis.
- Neural Signaling: The gut-brain axis is implicated in appetite control and metabolic regulation.
These mechanisms collectively contribute to sustained weight loss and resolution of comorbid conditions.
Indications for Bariatric Surgery
Bariatric surgery is indicated for patients with:
- Body Mass Index (BMI) ≥40 kg/m² (class 3 obesity) or
- BMI ≥35 kg/m² with obesity-related comorbidities such as type 2 diabetes, hypertension, obstructive sleep apnea, or dyslipidemia.
For Asian populations, lower BMI thresholds are recommended due to higher health risks at lower BMI levels.
Types of Bariatric Procedures
- Roux-en-Y Gastric Bypass (RYGB):
- Combines restriction and malabsorption.
- Creates a small gastric pouch and bypasses a portion of the small intestine.
- Effective for weight loss and metabolic improvements, particularly in T2DM.
- Sleeve Gastrectomy (SG):
- Restrictive procedure that removes approximately 80% of the stomach.
- Reduces ghrelin levels, leading to decreased appetite.
- Popular due to its simplicity and effectiveness.
- Laparoscopic Adjustable Gastric Banding (LAGB):
- Restrictive procedure involving an adjustable band around the upper stomach.
- Less invasive but associated with lower long-term success rates.
- Biliopancreatic Diversion with Duodenal Switch (BPD/DS):
- Combines restriction and significant malabsorption.
- Highly effective for weight loss but associated with higher complication rates.
Outcomes and Benefits
Bariatric surgery results in significant and sustained weight loss, typically 25–35% of body weight at 1 year and 15–25% at 20 years. Key benefits include:
- Improved Comorbidities: Resolution or improvement of type 2 diabetes, hypertension, dyslipidemia, obstructive sleep apnea, and other obesity-related conditions.
- Survival Benefit: Long-term studies, such as the Swedish Obese Subjects (SOS) study, demonstrate reduced mortality and lower incidence of cardiovascular events and cancer.
- Quality of Life: Patients report significant improvements in physical function, mental health, and overall well-being.
Metabolic Surgery
Bariatric surgery has been increasingly recognized for its metabolic benefits, particularly in treating type 2 diabetes. Procedures like RYGB and SG improve glycemic control, often before significant weight loss occurs. Mechanisms include enhanced GLP-1 secretion, improved insulin sensitivity, and changes in bile acid metabolism. Metabolic surgery is now considered a viable treatment option for patients with T2DM, even those with lower BMI levels.
Challenges and Considerations
Despite its benefits, bariatric surgery is not without risks. Potential complications include:
- Short-Term: Surgical site infections, bleeding, and anastomotic leaks.
- Long-Term: Nutritional deficiencies, dumping syndrome, and weight regain.
- Psychological: Patients may experience mood disorders or eating behavior changes.
Preoperative evaluation and postoperative follow-up are critical to minimizing risks and ensuring long-term success.
Conclusion
Bariatric surgery is the most effective treatment for severe and complex obesity, offering sustained weight loss, improved comorbidities, and enhanced quality of life. As the field continues to evolve, the focus has shifted from purely weight loss to addressing metabolic disorders, particularly type 2 diabetes. With ongoing research into the physiological mechanisms of these procedures, bariatric and metabolic surgery will remain a cornerstone in the management of obesity and its related conditions.
