Fat cells from patients who had lost weight after bariatric surgery, as well as from animals who had gained and then lost weight, were transcriptionally distinct from cells that had not experienced such weight changes at the organism level. In the animal studies, those transcriptional changes were due to epigenetic changes. The findings, which were published online in Nature on Nov. 18, 2024, are a possible molecular-level explanation for the short-term nature of most weight loss.