Does losing weight improve your GLP-1 production?
Research shows that weight loss through diet or exercise does not raise your fasting GLP-1; if anything, it falls slightly. Bariatric surgery does show a clearly improved GLP-1 response after eating.
GLP-1 is a gut hormone released after eating that helps regulate blood sugar and the feeling of fullness. Many people expect that losing weight improves the production of this hormone, but the research tells a different story: fasting GLP-1 actually falls slightly after weight loss through diet, exercise, or a combination of both. The more weight is lost, the more pronounced that drop. This was also the case in people with prediabetes or type 2 diabetes who followed a low-calorie, high-protein diet for six months and lost an average of around 8 kilograms.
That sounds contradictory, but this concerns the level measured while fasting, so before a meal. Whether the GLP-1 response to eating itself also changes is a separate question, and one that is less well covered by the available studies. In addition, the drop in fasting GLP-1 comes mainly from studies where participants were not assigned to groups at random; studies that did use random assignment found no clear effect. It is therefore not certain that weight loss is the actual cause of the change.
What the research does consistently show is that after weight loss the hunger hormone ghrelin rises clearly. This is a biological adaptation by the body that fuels hunger and can promote weight regain. Another fullness hormone also falls slightly, though that evidence is weaker. Losing weight therefore affects multiple hunger hormones at the same time, and those shifts tend to work against you rather than with you.
One exception is bariatric surgery, in which the digestive tract is extensively rerouted. After such a procedure, the GLP-1 response to a meal improves strongly, and a GLP-1 response to physical activity emerges that was not present before the operation. That effect was, however, measured in a small group of 13 women with severe obesity; how this plays out in other people has not yet been studied.
This answer draws on two studies that used random assignment and one large summary of many studies on weight loss and gut hormones. That combined summary rated the quality of the effects it found as moderate: the observed drop in fasting GLP-1 came exclusively from studies without random assignment; the more rigorously designed studies with random assignment found no clear effect. The weight-loss surgery study included only 13 participants. Strong, large-scale evidence on this topic is therefore not available.