People whose BMI falls below the usual obesity threshold can still meet a broader test for excess body fat, according to research published on November 11. But that finding does not automatically change who can receive a weight-loss medicine through England’s National Health Service, or NHS.
Daylight Post found that the study’s classification and the NHS funding rules answer different questions. Comparing the new research with current guidance shows that recognizing excess fat or related illness does not, by itself, meet the BMI requirements for a publicly funded prescription.
What BMI leaves out
BMI does not directly measure body fat. It is a useful first check, but it cannot show on its own where fat is carried or how a person’s organs are working.
The Nature study used records from more than 844,000 adults in China, Britain, the United States and Spain. Adding waist measurements identified some people in the BMI overweight category as having obesity-level body fat.
The researchers also distinguished excess fat without related loss of function from clinical obesity, where it affects organ function or daily life. These groups had different health risks. This was an analysis of existing records, not a trial showing which medicine should be offered to each group.
Record-based assessments have limits: not every study population had the same information on organ function, and the analysis could not establish the cause of illness in each individual.
Doctors are already asked to look beyond BMI
The National Institute for Health and Care Excellence, known as NICE, issues guidance on care and NHS treatment. Its existing adult assessment guideline already recommends using waist-to-height ratio alongside BMI for adults with a BMI below 35.
That ratio compares waist size with height, helping assess fat around the middle and associated health risks. The guideline also uses lower BMI thresholds for some ethnic backgrounds because health risks can arise at lower scores.
So the study is not evidence that current guidance tells clinicians to ignore the waist.
A funding threshold is another decision
For weight management, NICE recommends tirzepatide, sold as Mounjaro, for adults with an initial BMI of at least 35 and at least one weight-related health condition, alongside diet and physical-activity support. Qualifying BMI thresholds are normally 2.5 points lower for specified Asian, Middle Eastern, Black African and African-Caribbean backgrounds.
Tirzepatide helps reduce appetite and is also prescribed for type 2 diabetes under separate criteria.
Access is also being introduced in stages in England. NICE’s implementation information says the primary-care rollout currently prioritizes people with at least four specified weight-related conditions and BMI of 35 or more, with ethnic adjustments. Primary care includes family-doctor practices; specialist weight-management services are a separate route.
A person can therefore meet a research definition of obesity while remaining below the weight-management medicine threshold. That comparison identifies a difference in the tests used; it does not establish that everyone newly identified would benefit from tirzepatide.
NICE’s appraisal explains that it considered a broader group with BMI of at least 30 and a related condition, but did not recommend that group because its estimated benefits did not justify the cost to the NHS. Treatment access reflects that resource decision as well as how obesity is measured.