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    Obesity as a chronic disease

    Health bodies increasingly treat obesity as a chronic, relapsing disease rather than a lifestyle problem.[1] A 2025 Lancet Commission separated "clinical obesity", where excess fat is already harming organs, from "preclinical obesity", and said BMI alone should not be used to diagnose individuals.[2][3]

    Editor reviewedStrict sourcingUpdated GLP-1 and metabolic medicineHealth and medicine

    How obesity is defined decides who is offered treatment, what trials measure and what insurers pay for. Between 2025 and 2026 two influential bodies, WHO and a Lancet Commission, moved toward treating obesity as a chronic disease that needs long-term care.[1][2]

    How big the problem is

    WHO says obesity affects more than 1 billion people. It linked obesity to 3.7 million deaths in 2024.[4] In the US, the FDA says about 70% of adults have obesity or overweight.[5]

    From risk factor to disease

    For decades obesity was mostly measured with BMI, weight divided by height squared, and treated as a risk factor. In January 2025 a Lancet Diabetes & Endocrinology Commission proposed two categories.[6] Clinical obesity means excess body fat is already causing illness by changing how organs or the body work. Preclinical obesity means excess fat with organs still working normally, but with higher risk for the future.[2][7]

    The Commission defines clinical obesity as “a chronic, systemic illness” caused by excess or abnormal adiposity that alters tissue, organ or whole-person function. Preclinical obesity is excess adiposity with preserved organ function.[2][7] The Commission had 58 experts, reached 90–100% agreement on its recommendations, and was endorsed by 76 organisations.[6] The split matters for policy. It lets clinicians and payers tie drug treatment to evidence of organ harm rather than to a BMI threshold alone.[2]

    The trouble with BMI

    BMI cannot tell muscle from fat, so a muscular athlete can have a “high” BMI.[3] The Commission says BMI is fine for screening and population statistics. For an individual, excess fat should be confirmed another way, such as a waist measurement or a body-fat scan.[3]

    The Commission positions BMI as “a surrogate measure of health risk at a population level”. It asks that excess adiposity be confirmed by direct fat measurement or at least one anthropometric criterion such as waist circumference, waist-to-hip or waist-to-height ratio.[3] Current US drug labels still use BMI thresholds. Zepbound, for example, is indicated at BMI 30 or above, or 27 or above with a weight-related condition.[8]

    WHO’s 2025 guideline

    On 1 December 2025 WHO issued its first guideline on GLP-1 medicines for obesity. It makes conditional recommendations: adults may use the drugs for long-term treatment, and structured behavioural support should go with them.[9] WHO described obesity as “a chronic, relapsing disease”.[1] Earlier, in September 2025, WHO had added GLP-1 therapies to its Essential Medicines List for type 2 diabetes in high-risk groups.[10] WHO also warned that the drugs may reach fewer than 10% of people who could benefit by 2030.[11]

    Why “chronic” matters for treatment

    Calling obesity chronic has practical consequences. In trials where people stopped GLP-1 drugs, most of the lost weight came back. In the STEP 1 extension, participants regained about two-thirds of their weight loss within a year of stopping semaglutide.[12] Withdrawal of tirzepatide in SURMOUNT-4 led to a 14.0% regain over 52 weeks.[13] These results underpin the view that treatment may need to be long-term. That raises the cost and safety questions covered in the semaglutide page and the long-term use debate.[14]

    Questions readers ask

    What is the difference between clinical and preclinical obesity?

    The Lancet Commission defines clinical obesity as a chronic illness in which excess body fat is already altering how tissues or organs work. Preclinical obesity is excess fat with organ function preserved but a raised risk of future disease.[2][7]

    Is BMI still used?

    Yes, but the Commission recommends BMI as a population-level surrogate or screening tool. For individuals, excess fat should be confirmed with a direct fat measurement or another body measure such as waist circumference.[3]

    What does WHO recommend about GLP-1 drugs for obesity?

    WHO's first guideline, from December 2025, conditionally recommends that adults may use GLP-1 therapies for long-term obesity treatment, alongside behavioural interventions.[9]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      WHO's 2025 guideline describes obesity as a chronic, relapsing disease that needs comprehensive, lifelong care rather than medication alone. confirmedas of 2025-12-01

    2. [2]

      The Lancet Diabetes & Endocrinology Commission defines clinical obesity as a chronic, systemic illness in which excess or abnormal body fat alters the function of tissues, organs or the person. confirmedas of 2025-01-14

    3. [3]

      The Commission says BMI should serve as a population-level risk surrogate or screening tool, and that excess fat in individuals should be confirmed by direct fat measurement or at least one other body measurement such as waist circumference, partly because a high BMI can reflect muscle rather than fat. confirmedas of 2025-01-14

    4. [4]

      According to WHO, obesity affects more than 1 billion people and was linked to 3.7 million deaths in 2024. confirmedas of 2025-12-01

    5. [5]

      The FDA states that approximately 70% of American adults have obesity or overweight. confirmedas of 2023-11-08

    6. [6]

      The Commission, published on 14 January 2025, involved 58 experts and was endorsed by 76 organisations. confirmedas of 2025-01-14

    7. [7]

      The Commission defines preclinical obesity as excess body fat with preserved organ function but raised risk of developing clinical obesity and other diseases. confirmedas of 2025-01-14

    8. [8]

      On 8 November 2023 the FDA approved Zepbound (tirzepatide) for chronic weight management in adults with obesity, or overweight with at least one weight-related condition. confirmedas of 2023-11-08

    9. [9]

      On 1 December 2025 WHO issued its first guideline on GLP-1 medicines for obesity, with conditional recommendations that adults may use them for long-term treatment alongside behavioural interventions. confirmedas of 2025-12-01

    10. [10]

      In September 2025 WHO added GLP-1 therapies to its Essential Medicines List for type 2 diabetes in high-risk groups. confirmedas of 2025-12-01

    11. [11]

      WHO projects that even with expanded production, GLP-1 therapies will reach fewer than 10% of those who could benefit by 2030. confirmedas of 2025-12-01

    12. [12]

      One year after stopping semaglutide and lifestyle intervention in the STEP 1 extension, participants had regained about two-thirds of their prior weight loss, and most cardiometabolic improvements reverted toward baseline. confirmedas of 2022-05-19

    13. [13]

      In SURMOUNT-4, people who lost a mean 20.9% during a 36-week tirzepatide lead-in and were then switched to placebo regained 14.0% of body weight over the next 52 weeks, while those who continued lost a further 5.5%. confirmedas of 2024-01-01

    14. [14]

      A 2026 BMJ meta-analysis of 37 studies found average weight regain of 0.4 kg per month after stopping weight-management medicines, with cardiometabolic markers projected to return to baseline within 1.4 years, faster than after behavioural programmes. confirmedas of 2026-01-07

    Revision history (1)
    1. Page created.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "Obesity as a chronic disease." ContentLora, updated Oct 10, 2026. https://contentlora.com/explain/obesity-as-a-disease

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