Weight loss surgery works by altering the stomach and digestive system to influence hunger, fullness, metabolism, and energy balance.
Bariatric surgery disrupts the biological systems that defend excess body fat. Traditionally, these procedures reduce the stomach’s capacity (restrictive), alter nutrient absorption by bypassing part of the intestine (malabsorptive), or combine both approaches. However, the true impact of these surgeries goes far beyond anatomy. They influence hormones, gut-brain communication, and metabolic processes. Ongoing research continues to uncover how these complex mechanisms contribute to lasting weight loss and improved health.
Sleeve gastrectomy reduces the stomach to a narrow tube, allowing patients to feel full with much smaller meals. The procedure also removes the section of the stomach that produces the hunger hormone ghrelin, reducing appetite.
Faster movement of food into the small intestine triggers hormonal changes that regulate hunger and satiety. These combined effects help patients achieve significant, sustained weight loss while improving conditions such as diabetes and sleep apnoea.
Single-anastomosis gastric bypass and Roux-en-Y gastric bypass create a small stomach pouch and bypass the upper part of the small intestine, reducing absorption and altering hormone signaling. These surgeries lead to a significant rise in GLP-1, a hormone that boosts insulin release, slows stomach emptying, and reduces hunger.
Remarkably, many metabolic improvements—such as better blood sugar control and reduced sleep apnoea—occur within days to weeks, even before major weight loss begins. Research continues to explore how bypass surgery affects food preferences, energy expenditure, bile acids, gut bacteria, and vagus nerve signaling.
