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A new meta-analysis pooled results from 20 prospective cohorts thus investigating nearly 400,00 people (Weeldreyer et al, 2025). Participants were categorized by body mass index (BMI) as normal weight, overweight or obese. Their carodiorepiratory fitness (CRF) were measured by maximal exercise testing to determine if they were fit or unfit based on age adjusted VO2 max. This was to determine if BMI or CRF predicts mortality risk better.
This meta-analysis is different from earlier ones since it includes more women. It also has participants from a broader age range, geographic backgrounds and health status. Better statistics all round. Findings more generalizable and results more precise.
The reference group - normal weight and fit was compared to all other combinations. Compared to the reference group, those who were both overweight but fit and obese but fit, both groups had virtually the same risk of dying from any cause. About 4 percent lower and 11 percent higher respectively, which was not statistically significant. Being fit protected against being overweight and obese for all-cause mortality.
Not so good news for the unfit. Those who had normal weight but were unfit had a 92 percent higher all-cause mortality risk. The risk was similarly high for unfit and overweight (82 percent higher) and even higher for the unfit and obese (104 percent higher).
For cardiovascular disease mortality, the differences between weight categories were more pronounced. The fit but overweight had a 50 percent higher risk while those fit and obese had a 62 percent higher risk than fit individuals with normal weight. Note that neither was significant, although it meant that being fit protected one against the risk of dying from cardiovascular disease.
Now for those who were unfit for cardiovascular disease mortality, the numbers were not pretty, in fact they shyrocketed. 104 percent higher risk for normal weight, 158 percent for overweight and 235 percent for the obese.
In short, being unfit more than doubled mortality risk for many cases, regardless of BMI, while being fit can netralize the impact of carrying extra weight.
These findings show that BMI alone is a weak predictor of health and improving cardiorespiratory fitness can cancel out much of the risks associated with a higher BMI.
Perhaps BMI is not a good indicator. One may have a high BMI and yet be muscular and fit - the Amercian football players in the NFL have high BMI values. They are classified as obese, but they are actually very fit and muscular.
Should we be more concerned with increasing fitness levels over weight loss during public health awareness? There seems to be more emphasis now on weight loss and eating less processed food rather than increasing physical activity.
This study suggests boosting fitness levels should be at the top of the list, not just as a replacement for tackling obesity. Studies like this show that physical activity is definitely more important than diet for those who want to live to a ripe, old healthy age. Not to say that diet does not matter. But fitness is king. Perhaps our Ministry Of Health should angle some incentives?
Reference
Weeldreyer NR, De Guzman JC, Paterson C et al (2025). Cardiorespiratory Fitness, Body Mass Index And Mortality: A Systematic Review And Meta-Analysis. BJSM.59:339-346. DOI: 10.1136/bjsports-2024-108748