Obesity: Limited trend data covering recent decades support significant growth of BMI ≥40 population since the 1980s

Rising prevalence of BMI ≥40 kg/m2: A high‐demand epidemic needing better documentation. Kath Williamson, Amy Nimegeer, Michael Lean. Obesity Reviews, February 4 2020, https://doi.org/10.1111/obr.12986

Summary: Whilst previously rare, some surveys indicate substantial increases in the population with body mass index (BMI) ≥40 kg/m2 since the 1980s. Clinicians report emerging care challenges for this population, often with high resource demands. Accurate prevalence data, gathered using reliable methods, are needed to inform health care practice, planning, and research. We searched digitally for English language sources with measured prevalence data on adult BMI ≥40 collected since 2010. The search strategy included sources identified from recent work by NCD‐RisC (2017), grey sources, a literature search to find current sources, and digital snowball searching. Eighteen countries, across five continents, reported BMI ≥40 prevalence data in surveys since 2010: 12% of eligible national surveys examined. Prevalence of BMI ≥40 ranged from 1.3% (Spain) to 7.7% (USA) for all adults, 0.7% (Serbia) to 5.6% (USA) for men, and 1.8% (Poland) to 9.7% (USA) for women. Limited trend data covering recent decades support significant growth of BMI ≥40 population. Methodological limitations include small samples and data collection methods likely to exclude people with very high BMIs. BMI ≥40 data are not routinely reported in international surveys. Lack of data impairs surveillance of population trends, understanding of causation, and societal provision for individuals living with higher weights.

4.3 Strengths and limitations

This review has concentrated on robustly measured data to establish the international prevalence rates for BMI ≥40. Whilst the rationale for exclusion of self‐report data is sound, in that it commonly underestimates BMI, the exclusion also acts as a limitation, for example, by excluding EHIS data, which covers many European countries. The sample sizes possible with measured data are reduced by the need for resources to make measurements, and there is potential bias against including very heavy individuals whose mobility is impaired. In some cases, the upper limit of scales excluded the heaviest individuals. These limitations would tend to underestimate the true prevalence of the highest BMI categories, not overestimate.
Applying a lower threshold of BMI ≥35 would have broadened the available data, whilst potentially weakening the focus on the highest BMI category, where costs and clinical complexity is greatest. Some studies report the lower threshold of BMI ≥35 particularly those examining Asian populations where different BMI cut‐offs relating to overweight and obesity are often applied.98
Limiting the review to the English language prevented examination of some original data sources, which could only be located in their native language, for example, Spanish for Chile and Mexico. It was not possible to locate English versions of these, and resources did not allow for translation. The OECD reports these original sources in English in its database, but only at BMI thresholds of 25.0 to 29.9 and BMI ≥30, with prevalence for Chile and Mexico the highest in the world, above even those of the United States.99 Thus, they are likely to have significant BMI ≥40 prevalence. Additionally, whilst the search processes were broad, encompassing a variety of sources and used systematic methods, they were not exhaustive, as might be expected from a formal systematic literature review or meta‐analysis. We believe that they represent a reliable summary of the current evidence base on BMI ≥40, as it is available to decision makers. Some individual sources have not been included, notably those from non‐English publications, but they are unlikely to alter the very consistent conclusions.