Redefining obesity:
From risk factor to disease
As of 2022-2023, 64% of adults aged 18 and over in England were estimated to be overweight or living with obesity, highlighting the need to address obesity not just as a risk factor, but as a disease that requires comprehensive medical attention.[1]
It is, however, important to consider that many statistics are primarily based on Body Mass Index (BMI), a measure that has its limitations and complexities.
In this article, Paul Edwards, Underwriting Research & Systems Development Manager at the Hannover Re UK Life Branch, explores the evolving medical perspective on obesity as a disease and its implications for underwriting and claims assessment, particularly in light of the complexities of BMI and emerging diagnostic criteria, and advancements in treatment options.
The Lancet Commission on Obesity reported its recommendations in January 2025 (Rubino et al, 2025) [2]. Its key finding is a drive to alter the perception of obesity as merely a risk factor but instead to treat
“...clinical obesity [as an] illness that [is] akin to the notion of chronic disease in other medical specialities”.
The Commission focused on defining what is preclinical and clinical obesity, with the first being:
“a state of excess adiposity with preserved function of other tissues and organs [but with an] increased, risk of developing obesity and several other non-communicable diseases”
Clinical obesity is however
“a chronic systemic illness characterised by alterations in the function of tissues, organs, the entire individual…due to excess adiposity”
The Commission recognised that the redefinition could be problematic if obesity is only based on BMI. Firstly, it would mean 26% of the population would be classified as having a disease [3], and secondly, it would both miss those at risk (particularly people who have a BMI of 26-30 kg/m2) but have central or organ-related excess adiposity, while continuing to categorise those who have no risk, particularly muscular elite athletes.
“Based on BMI, Arnold Schwarzenegger when he was a bodybuilder would have been categorised as obese and needing to lose weight.”
Dr. Wajahat Mehal, director of the Metabolic Health and Weight Loss Program at Yale
Instead, in addition to BMI (unless the person has a BMI of >40 kg/m2), the Commission recommends that a diagnosis of preclinical obesity should only be made if at least one further measure of excess adiposity occurs (waist circumference, waist to height ratio, waist to hip - see box to the right) or if excess body fat is measured directly, for example, using a DEXA (dual-energy X-ray absorptiometry) scan.
1. Waist circumference >88cm or 102cm for women and men respectively
2. Waist-to-hip ratio >0.90 for men & >0.85 for women
3. Waist-to-height ratio >0.50 for all
Anyone with BMI of >40 kg/m2 is assumed obese
A diagnosis of clinical obesity should only be made if all the above criteria are met and the person has either signs or symptoms of ongoing dysfunction in any organs and/or any limitations in mobility or other basic activities of daily living (e.g., bathing, dressing, toileting, continence, and eating).
Figure 2: Clinical assessment of obesity, after Rubino et al 2025
Why does this matter? At the very least, it will help target people for therapeutic intervention or monitoring. In particular, in the era of revolutionary weight loss medications (GLP-1 antagonists), it will help physicians decide if those medications can be prescribed, irrespective of whether a person has crossed an arbitrary threshold (BMI > 35 kg/2 for example).
These medications work by mimicking better the effects of incretin hormones that are produced in the gastrointestinal tract. These bind to GLP-1 (glucagon-like peptide-1) receptors in the pancreas. By binding to these receptors GLP-1 drugs then stimulate insulin release and reduce the amount of glucose synthesised in the liver. As a secondary effect it slows down the rate at which food is absorbed into the blood and in turn stimulates a feeling of fullness and helps to reduce appetite.
In the protection insurance setting, the use of BMI has a venerable history. For example, after noticing an increase in claims from their obese customers, The Metropolitan Life Insurance Company introduced a stratification process in 1953, categorising applicants as having small, medium, or large frames based on their weight and height.[4]
At Hannover Re UK, we have recognised the imperfections of BMI for some time and advocated the use of waist circumference as moderator of BMI since 2010, with a new model of assessing both introduced in our underwriting manual hr|Ascent in 2020.
Waist circumference is considered a better predictor of cardiometabolic risks because it more accurately reflects visceral fat distribution, which is strongly linked to conditions like diabetes and cardiovascular disease. Like BMI, waist circumference is easy to measure, but unlike a scan, it is non-invasive, cost-effective, and widely accessible, making it a practical tool.
Figure 3: Cardiometabolic risks by BMI category after Kuk 2018
This approach enables us to better identify the 20% of people with a healthy BMI or the 50% of those classified as ‘overweight’ who have cardiometabolic risks, while avoiding unnecessary penalisation of the 35% of people categorised as ‘obese’ who do not.[5]
The advantages of using waist circumference measurements over BMI go beyond merely classifying obesity. Obesity significantly raises the risk of heart disease, type 2 diabetes, and certain cancers. Excess body fat can result in high blood pressure, insulin resistance, and chronic inflammation, all of which contribute to these serious health conditions.[6]
For example, recent research published in JAMA Network Open has shown that central obesity measures, such as waist circumference and waist-to-hip ratio, are more accurate than BMI in estimating the risk of colorectal cancer (CRC). The study analysed data from over 450,000 individuals and found that these central obesity measures had stronger associations with CRC incidence compared to BMI. These findings suggest that waist measurements may provide a better assessment of health risks related to obesity, highlighting the need for clinicians to consider these measures in their practice.[7]
Conclusion
As obesity is increasingly recognised as a disease rather than just a risk factor and given these new guidelines, it is time for insurers to adopt the use of waist measurement in addition to capturing both height and weight. Indeed, this is something that we have been advocating at Hannover Re for over a decade, and our manual hr|Ascent has an in built calculator and philosophy designed specifically for this. In addition, given the unprecedented wave of news related to weight loss drugs and their uptake by the general public, a wholesale review of application forms and how they capture their use, and their impact is also urgently required.
Author
Paul Edwards
Underwriting Research & Systems Development Manager
Hannover Re UK Life Branch
Tel. +44 7584 529136
paul.edwards@hannover-re.com
References
Header image: Jelena Stanojkovic.stock.adobe.com
- Office of National Statistics, Obesity Profile
Obesity Profile: short statistical commentary May 2024 - GOV.UK
2. Rubino, Francesco et al. Definition and diagnostic criteria of clinical obesity
The Lancet Diabetes & Endocrinology Commission, January 2025 doi: 10.1016/S2213-8587(24)00316-4
3. Office of National Statistics, Obesity Profile
Obesity Profile: short statistical commentary May 2024 - GOV.UK
4. Pray R, Riskin S. The History and Faults of the Body Mass Index and Where to Look Next: A Literature Review. Cureus. 2023 Nov 3;15(11):e48230. doi: 10.7759/cureus.48230. PMID: 38050494; PMCID: PMC10693914.
5. Kuk, J.L et al Individuals with obesity but no other metabolic risk factors are not at significantly elevated all-cause mortality risk in men and women. Clinical Obesity May 2018
Figure 4 image: pikovit.stock.adobe.com
6. Health Risks of Overweight & Obesity - NIDDK
7. Central obesity metrics more accurate than BMI in estimating excess weight-related CRC
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