{
  "abstract": "Background/Objectives: Whether the loss of fat-free mass (FFM) during tirzepatide treatment exceeds the proportion expected in negative energy balance is debated, and the earliest weeks of treatment are the least characterized. We described the body-composition trajectory over the first 12 weeks of treatment in routine care. Methods: In this retrospective cohort of adults with obesity starting tirzepatide monotherapy, body weight, fat mass, FFM, total body water (TBW), and waist circumference were measured by single-frequency, foot-to-foot bioelectrical impedance analysis (BIA) at baseline and at approximately 4, 8, and 12 weeks, and were analyzed with linear mixed-effects models; follow-up values are available-data, on-treatment estimates. Results: Of 476 patients (mean age 40 years, 66% female, mean body-mass index 38.7 kg/m2), 268 had follow-up data and 111 were measured at 12 weeks. Estimated marginal body weight fell by 11.22 kg (10.4%), fat mass by 7.90 kg (16.8%), and BIA-derived FFM by 3.35 kg (5.4%) at 12 weeks (all p < 0.001); assuming 5-kg-less loss in patients without a 12-week measurement, the mean loss remained 7.4 kg. Of patients measured at 12 weeks, 89.2% had lost at least 5% and 57.7% at least 10% of body weight. In patients with complete data at baseline and 12 weeks (n = 85), fat mass accounted for 68.3% (95% CI 56.1 to 80.8) of the weight lost. Conclusions: Early weight loss during tirzepatide treatment was predominantly fat mass, with a BIA-derived FFM fraction numerically close to the commonly cited one-fourth. Because device-FFM equaled TBW divided by a fixed coefficient of 0.731 at every visit, it cannot separate water from lean tissue and is best read as an upper bound on lean tissue loss rather than a measure of muscle.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Internal Medicine, Sakarya University Training and Research Hospital, 54100 Sakarya, Turkey",
    "Department of Internal Medicine, Faculty of Medicine, Sakarya University, 54100 Sakarya, Turkey"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Enes Zafer",
      "orcid": "0009-0001-4547-0255"
    },
    {
      "affs": [
        0
      ],
      "name": "Deniz Çekiç",
      "orcid": "0000-0002-7114-9334"
    },
    {
      "affs": [
        1
      ],
      "name": "Ahmed Bilal Genç",
      "orcid": "0000-0002-1607-6355"
    },
    {
      "affs": [
        1
      ],
      "name": "Selçuk Yaylacı",
      "orcid": "0000-0002-6768-7973"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/0y5yf41dez4s8.bib",
  "cited_by": 0,
  "doi": "10.3390/jcm15218377",
  "fulltext_url": null,
  "id": "0y5yf41dez4s8",
  "issns": [
    "2077-0383"
  ],
  "landing_url": "https://www.mdpi.com/2077-0383/15/21/8377",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2736|Pharmacology and Obesity Treatment"
    ]
  ],
  "openalex": "W7224129247",
  "pdf_url": null,
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-28",
  "publisher": "MDPI AG",
  "ris": "https://research.draconitic.com/paper/0y5yf41dez4s8.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:01Z",
      "native_id": "10.3390/jcm15218377",
      "source": "crossref",
      "url": "https://www.mdpi.com/2077-0383/15/21/8377"
    }
  ],
  "subjects": [
    {
      "field": "medicine",
      "origin": "openalex:2736|Pharmacology and Obesity Treatment",
      "subfield": "pharmacology-toxicology"
    }
  ],
  "title": "Early Body-Composition Trajectory During Tirzepatide Treatment for Obesity: A Real-World Bioimpedance Cohort Study",
  "title_text": "Early Body-Composition Trajectory During Tirzepatide Treatment for Obesity: A Real-World Bioimpedance Cohort Study",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:20:01Z",
  "url": "https://research.draconitic.com/paper/0y5yf41dez4s8",
  "venue": "Journal of Clinical Medicine",
  "versions": []
}