UCL study: 69% of UK adults with BMI-defined obesity had preclinical form at age 46

Researchers from University College London, the UCLH NIHR Biomedical Research Centre and Barts Health NHS Trust compared a new clinical obesity classification with body mass index (BMI) categories in 6,978 British adults aged 46, according to news-medical.net. The work was published in the International Journal of Obesity. About 69% of people with obesity by BMI had preclinical rather than clinical obesity news-medical.netnews-medical.netnews-medical.netOpen source ↗.

BMI is widely used but criticised because it does not capture fat distribution, does not separate fat from muscle, and ignores differences by sex, age and ethnicity. The new definition, commissioned by the Lancet, separates no obesity, preclinical obesity and clinical obesity using three components: excess adiposity, organ dysfunction and functional limitations.

Data and classification

The authors used the age-46 follow-up wave of the 1970 British Cohort Study, a nationally representative birth cohort, which included biomedical assessments, questionnaires and interviews. Of 8,581 participants, 81.3% had data for both classifications. Body composition, waist measurements, health reports and functional assessments were used to approximate the diagnostic criteria.

People without excess adiposity were classed as having no obesity. Excess adiposity without organ dysfunction or functional limitations meant preclinical obesity; with either or both, clinical obesity. WHO BMI thresholds were applied in parallel: underweight below 18.5 kg/m², healthy 18.5 to below 25, overweight 25 to below 30, and obesity 30 or above news-medical.netnews-medical.netnews-medical.netOpen source ↗.

Results and limits

Among the 6,978 included participants, 52.5% had preclinical obesity, 17.7% clinical obesity and 29.8% no obesity. By BMI, 0.7% were underweight, 29.1% healthy, 37.8% overweight and 32.4% had obesity.

Only 31.4% of those with BMI-defined obesity met clinical obesity criteria. In the overweight BMI group, 65% had preclinical obesity, 16.6% clinical obesity and 18% no obesity. Agreement between the two systems was stronger in women than in men.

Twenty-seven participants died by age 51. Clinical obesity was associated with higher five-year mortality odds than no obesity. The result for preclinical obesity was statistically inconclusive, and BMI-defined overweight or obesity showed no significant association with mortality. The authors note the small number of deaths limits this evidence news-medical.netnews-medical.netnews-medical.netOpen source ↗.

Clinical obesity prevalence may be underestimated, since participants missing adiposity assessments had higher average BMIs. The authors say further studies must validate the criteria across ages, sexes, ethnicities and settings, and show that they improve long-term risk prediction before use in individual clinical decisions.