Will the New Lancet Commission Classification of Obesity Only Mystify and Complicate Things in Paediatric Clinics?

Abstract

In January 2025, a new classification of obesity was published in the Lancet Diabetes & Endocrinology [1]. It was developed by The Lancet Commission on the Definition and Diagnosis of Clinical Obesity, which comprised more than 50 researchers and experts in the field. The contributors should be praised for their enormous efforts and for including people living with obesity to ensure that the new classification included perspectives from patients. However, despite the appealing graphics that aim to explain the new criteria, the approach has left even insightful readers with doubts.

So what does the new classification say? The first option is that people who used to fulfill the simple body mass index (BMI) criteria for overweight or obesity would no longer receive a diagnosis. The second is that, after careful consideration, they could meet the definitions for diagnoses of pre-clinical obesity or clinical obesity. Overweight, a general term that has often been used to describe both overweight and obesity in daily speech, but has lacked the status of a diagnosis, seems obsolete.

The 42-page Commission's report will now challenge the printers in many obesity clinics. Having read it, I can summarise it as follows. It is not enough with a high BMI to be diagnosed with clinical obesity. Measurements that indicate increased body fat will be needed for a diagnosis, such as the patient's fat percentage, waist circumference, waist-to-height ratio or waist-to-hip ratio. In addition, symptoms that indicate problems, such as pain or affected blood tests, are needed. With all due respect to the Commission, the operational definitions are unclear for many of the 18 criteria for adults and 13 for children. Just consider this criterion for paediatric patients: ‘cluster of hyperglycemia/glucose intolerance with abnormal lipid profile (high triglyceride levels or high LDL cholesterol or low HDL cholesterol)’. Note the word ‘with’ which tells us that glucose intolerance without lipid disturbances or even manifest type 2 diabetes is not included as a criterion. Similarly, a criterion like polycystic ovary syndrome is hard to define in girls. Another issue is that the prerequisites for diagnosing clinical obesity, namely body fat percentage or waist circumference, do not have clear and generally accepted cut-offs for children [2].

Those who like an academic battle could go on debating diagnostics, degrees and definitions forever, but that takes a lot of human power away from treating the patients we see in our clinics.

The coverage in the general, non-medical media has been respectful, but two well-respected UK titles have raised concerns. The Guardian remarked that the health challenges of curbing obesity remain [3]. Meanwhile, The Economist saw the need to decide ‘who is sick and who is not’, [4] suggesting that there needs to be a distinction in the era of new and effective, but costly, anti-obesity drugs.

The current definitions of overweight and obesity cover about a fifth of the children in Sweden [5] and a change in the diagnostic criteria will clearly matter. Today, we use the cut-offs that are visible in all growth charts to determine whether a child has a normal weight for their age and sex. These help us to diagnose overweight or obesity, and if needed, divide the latter into obesity grades 1–3 [6].

Using BMI charts to diagnose obesity is easy to do in clinics and it is also easy to teach. It takes 2 s to determine whether a child is above the cut-off points for overweight or obesity, but it takes skill and experience to communicate the diagnosis to the child and family.

We make the diagnosis and take it from there. Many children with obesity are well, while others are more affected. But we make sure that we stress the positives and appreciate all signs of good health. We determine whether the child has uncomplicated obesity or whether complications are already present. And then we start to try and change the course of weight development and prevent the progression into more severe degrees of obesity and more complications. Health care providers will refer children with obesity grade 2 or 3, or complications, to higher levels of care for more intense treatments.

Obesity hampers a child's ability to move, play, sleep and perform at school. Many children with obesity have concomitant diseases that make things more complex, such as neuropsychiatric comorbidities. Many have psychosocial challenges. These appear to be missing from the list of criteria produced by the Commission and they are often the most important aspects.

Most children and adolescents with obesity remain with obesity during their adult years [7]. We also know that two children of the same height, sex, and age can have different BMIs and these can largely be explained by variations in the amount of body fat. Muscle growth is limited before puberty and cannot explain a high BMI. We try hard to cater to patients' individual needs and reduce stigma of all kinds.

It is interesting that Putri et al. published a critical study in JAMA Paediatrics just after the Lancet Commission paper appeared. The study, which used data from the Swedish Childhood Obesity Treatment Register, illustrates the benefits of diagnosing obesity using established methods. It showed that children who had effective treatment for obesity in childhood had reduced risks of mortality and lower risks for diseases like type 2 diabetes in adulthood, unlike children for whom treatment was not as effective [8]. An editorial on the paper, by Epstein et al., concluded that the study was probably the first to demonstrate the impact of paediatric treatment for obesity on cardiometabolic disease and mortality in young adulthood [9].

Obesity per se can safely remain a diagnosis for children, and it should entitle them and their families to the care they need to help them preserve their future health. We need a straightforward and relevant classification that can be easily communicated to parents and other stakeholders. Instead of battling over criteria, we need to focus our attention on disseminating and following the most useful guidelines [10].

It would be great to agree on a global reference on overweight and obesity, as there are several international and national references that have been used to develop the different BMI charts used across the world. Having different references definitively makes international comparisons difficult. However, I believe there is no need to mystify and complicate things further for clinicians dealing with children's weight issues. While I applaud the scrutiny that the Lancet Commission experts have paid to this subject, I would rather stick to my present BMI growth charts for diagnosis.

Annika Janson: conceptualization, writing – original draft.

The author declares no conflicts of interest.