In healthy adults, insulin secretion rate tracked blood glucose about 6±1 minutes ahead, with GLP-1 running roughly 9±3 minutes ahead of glucose, a feed-forward signal that primes beta cells. In obesity and prediabetes, GLP-1 and insulin secretion fell off prematurely, prolonging post-meal hyperglycemia. Semaglutide raised insulin output and curbed hyperglycemia, but erased the lead: insulin and glucose profiles overlapped, and post-meal glycemic undershoots rose.
The work reframes beta-cell dysfunction as a loss of timing, not just insufficient insulin volume. That matters because GLP-1 drugs are now used for obesity and diabetes by millions, and the finding suggests their benefit comes from brute-force stimulation rather than restored physiology. The undershoot signal is the clinically interesting part: reactive lows after meals could plausibly explain some patient-reported symptoms, though this preprint does not test symptoms or outcomes. Key limitations include the fine-grained, likely small-cohort physiological design (the abstract gives no sample sizes), inference of ISR from deconvolution of C-peptide data rather than direct measurement, and no evidence that the timing shift affects long-term cardiometabolic outcomes. Semaglutide's proven benefits for weight, glycemia, and cardiovascular events are not challenged here. This is a preprint that has not been peer reviewed, so the quantitative timing estimates may change. Mechanistically novel and hypothesis-generating rather than practice-changing; patients should not alter treatment based on it, but it may inform future dosing and combination strategies.