There are three main ways obesity numbers are produced. Knowing which one you are looking at helps you read any chart correctly.
1. Measuring people
Trained survey staff weigh people on scales and measure their height. The US National Health and Nutrition Examination Survey (NHANES) works this way — and it found 40.3% of US adults (20+) had obesity in Aug 2021–Aug 2023.
2. Asking people
Phone or school surveys ask people for their own height and weight. This is cheaper, so it can cover every state or school, but it can be less accurate. The CDC’s phone survey (BRFSS) found these figures for US adults (18+) over roughly the same years:
- Measured (NHANES, Aug 2021–Aug 2023)40.3%
- Self-reported (BRFSS, 2021)33.0%
- Self-reported (BRFSS, 2022)33.3%
- Self-reported (BRFSS, 2023)32.8%
The two surveys also differ in age range (20+ vs 18+) and method (age-adjusted vs not), so this illustrates the gap rather than giving an exact comparison. Sources: CDC NHANES (our calculation); CDC BRFSS.
3. Estimating with models
Not every country runs a survey every year. The World Health Organization, working with a network of scientists called NCD-RisC, combines the available surveys to estimate every country and every year from 1980 to 2024. That is why WHO figures come with an uncertainty range — the shaded bands on our charts. The true value is likely to be inside that range.
Where we show a number of people (for example about 944 million adults with obesity worldwide in 2024), we multiplied WHO’s rate by the UN’s population estimate. See the methodology.
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Written by the ObesitySurvey team. Not medical advice.