The global obesity epidemic is well-documented, with two in five adults classified as overweight or obese. Public health guidance has long focused on weight loss to address the associated risks of cardiovascular disease (CVD) and mortality. However, recent research suggests that cardiorespiratory fitness (CRF) may be a more critical factor in predicting mortality than body mass index (BMI).
This raises the question, can you be "fat and fit"?
Or indeed, fat and - more to the point - healthy? This has been an ongoing question for many years, so what does the latest research say? We will contrast this with an older study from the UK that shows different results.
As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to relevant studies and resources at bottom of page.
Fitness Trumps Fatness
A meta-analysis of 20 studies (Weeldreyer et al, 2024), encompassing nearly 400,000 individuals, has provided compelling evidence that fitness is a stronger determinant of mortality risk than BMI. The study revealed that individuals with higher CRF level, regardless of their weight, did not face an increased risk of all-cause or CVD mortality compared to normal-weight fit individuals. Conversely, those categorised as unfit experienced a two to threefold increase in mortality risk, regardless of their BMI classification.
Being unfit greatly increased the risk of death, regardless of weight.
Normal weight and unfit people had:
2 times the risk of dying from CVD compared to the fit-normal weight group.
1.9 times the risk of dying from any cause.
Overweight and unfit people had:
2.6 times the risk of dying from CVD.
1.8 times the risk of dying from any cause.
Obese and unfit people had the highest risks:
3.4 times the risk of dying from CVD.
2 times the risk of dying from any cause.
Interestingly, the analysis demonstrated that even moderate levels of fitness, defined as surpassing the 20th percentile of age-adjusted CRF, were sufficient to significantly reduce mortality risks. These findings highlight the importance of physical activity in promoting longevity, independent of weight loss.
CRF improves health in multiple ways that go beyond the scale. Physical activity enhances cardiovascular function, reduces inflammation, and improves insulin sensitivity—all factors linked to a lower risk of chronic diseases and mortality. Importantly, the metabolic health benefits of exercise are observed even in individuals who remain overweight or obese.
Despite these findings, the study noted that obesity's association with type 2 diabetes and other CVD risk factors may attenuate but not entirely eliminate the mortality risk, even in fit individuals.
This suggests that while fitness mitigates many of the health risks associated with high BMI, it may not fully negate them.
A UK Perspective
Researchers (Caleyachetty, 2016) analysed health records from 3.5 million adults in the UK, tracking their cardiovascular health over 5.4 years. Participants were grouped by body size (underweight, normal weight, overweight, and obese) and the presence of metabolic abnormalities such as diabetes, hypertension and high cholesterol. The study focused on the first occurrence of major cardiovascular conditions: coronary heart disease (CHD), cerebrovascular disease (like strokes), heart failure, and peripheral vascular disease. What did they find?
Obese but "Metabolically Healthy" Individuals:
Obese people with no metabolic abnormalities were at 49% higher risk of CHD compared to normal-weight individuals without metabolic issues.
They were also at 7% higher risk of cerebrovascular disease and nearly 2 times the risk of heart failure.
This challenges the idea that being metabolically healthy offsets the risks associated with obesity. Being obese, even without traditional risk factors like diabetes or high blood pressure, still increases the risk of major cardiovascular diseases compared to those of normal weight with no metabolic problems.
Impact of Metabolic Abnormalities:
Across all body sizes (normal weight, overweight, and obese), having more metabolic abnormalities (e.g., diabetes, high blood pressure, high cholesterol) significantly increased the risk of cardiovascular diseases.
Even normal-weight individuals with metabolic issues faced similar risks as their overweight or obese counterparts.
Metabolic Health is Key:
Regardless of body size, metabolic abnormalities such as diabetes, high blood pressure, and high cholesterol are strong predictors of cardiovascular risk.
Normal-weight individuals with metabolic issues are not "safe" from heart disease and have similar risks as those who are overweight or obese.
Cardiovascular disease risk is influenced by both body size and metabolic health. While maintaining a healthy weight is important, addressing metabolic abnormalities is critical for reducing the risk of heart disease, stroke, and heart failure. This study underscores the need for health strategies that focus on improving metabolic health, regardless of body size.
Final Thoughts
The evidence is clear: both fitness and metabolic health play critical roles in determining cardiovascular and overall mortality risks.
While the notion of being “fit but fat” has merit, highlighting the protective effects of cardiorespiratory fitness against mortality, this does not mean weight or metabolic health can be ignored.
The research from Weeldreyer et al. demonstrates that fitness reduces mortality risks across all BMI categories, even for those classified as overweight or obese. Moderate levels of CRF, achievable through consistent physical activity, significantly lower the risk of cardiovascular disease and all-cause mortality. Fitness enhances cardiovascular function, reduces inflammation, and improves metabolic markers, offering a powerful shield against many health risks.
However, the UK study by Caleyachetty et al. adds an important nuance. It shows that obesity, even in the absence of metabolic abnormalities, still increases the risk of major cardiovascular diseases such as coronary heart disease and heart failure. Furthermore, individuals of normal weight who have metabolic abnormalities face similar risks to their overweight or obese peers, underscoring that metabolic health is just as vital as fitness and weight management.
The interplay between fitness, fatness, and metabolic health is complex. A focus solely on weight loss may overlook the benefits of fitness, while ignoring metabolic health can leave significant risks unaddressed. For optimal health and longevity, health strategies should prioritise improving CRF through physical activity while addressing metabolic abnormalities, regardless of body size. Eating well, having fun with (or gaining satisfaction from) physical activity and good sleep are great places for anyone to start. And a holistic approach offers the best path to reducing the burden of cardiovascular disease and enhancing quality of life.
Improving health is about finding motivation, prioritising self-care and taking action. If you want to take effective and targeted steps that fit into your unique lifestyle, The Whole Health Practice is here to help.
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Stay Healthy,
Alastair
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Related Studies
The study in question: Weeldreyer NR, De Guzman JC, Paterson C, et al, Cardiorespiratory fitness, body mass index and mortality: a systematic review and meta-analysis, British Journal of Sports Medicine Published Online First: 13 November 2024. doi: 10.1136/bjsports-2024-108748
Other
González-Gálvez N, López-Martínez AB, López-Vivancos A. Clustered Cardiometabolic Risk and the "Fat but Fit Paradox" in Adolescents: Cross-Sectional Study. Nutrients. 2024 Feb 22;16(5):606. doi: 10.3390/nu16050606. PMID: 38474733; PMCID: PMC10934411.
Kokkinos P, Faselis C, Samuel IBH, Pittaras A, Doumas M, Murphy R, Heimall MS, Sui X, Zhang J, Myers J. Cardiorespiratory Fitness and Mortality Risk Across the Spectra of Age, Race, and Sex. J Am Coll Cardiol. 2022 Aug 9;80(6):598-609. doi: 10.1016/j.jacc.2022.05.031. PMID: 35926933.
Valenzuela PL, Santos-Lozano A, Barrán AT, Fernández-Navarro P, Castillo-García A, Ruilope LM, Ríos Insua D, Ordovas JM, Ley V, Lucia A. Joint association of physical activity and body mass index with cardiovascular risk: a nationwide population-based cross-sectional study. Eur J Prev Cardiol. 2022 Mar 11;29(2):e50-e52. doi: 10.1093/eurjpc/zwaa151. Erratum in: Eur J Prev Cardiol. 2021 Dec 20;28(14):1620-1621. doi: 10.1093/eurjpc/zwab053. PMID: 33580798.
Ezzatvar Y, Izquierdo M, Núñez J, Calatayud J, Ramírez-Vélez R, García-Hermoso A. Cardiorespiratory fitness measured with cardiopulmonary exercise testing and mortality in patients with cardiovascular disease: A systematic review and meta-analysis. J Sport Health Sci. 2021 Dec;10(6):609-619. doi: 10.1016/j.jshs.2021.06.004. Epub 2021 Jun 29. PMID: 34198003; PMCID: PMC8724619.
Barry VW, Caputo JL, Kang M. The Joint Association of Fitness and Fatness on Cardiovascular Disease Mortality: A Meta-Analysis. Prog Cardiovasc Dis. 2018 Jul-Aug;61(2):136-141. doi: 10.1016/j.pcad.2018.07.004. Epub 2018 Jul 5. PMID: 29981352.
Caleyachetty R, Thomas GN, Toulis KA, Mohammed N, Gokhale KM, Balachandran K, Nirantharakumar K. Metabolically Healthy Obese and Incident Cardiovascular Disease Events Among 3.5 Million Men and Women. J Am Coll Cardiol. 2017 Sep 19;70(12):1429-1437. doi: 10.1016/j.jacc.2017.07.763. PMID: 28911506.
Högström G, Nordström A, Nordström P. Aerobic fitness in late adolescence and the risk of early death: a prospective cohort study of 1.3 million Swedish men. Int J Epidemiol. 2016 Aug;45(4):1159-1168. doi: 10.1093/ije/dyv321. Epub 2015 Dec 20. PMID: 26686843.
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