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‘Fat but fit’ body type increases risk for all-cause death in men with obesity
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Normal-weight men who are not physically fit are less likely to die of any cause than men with obesity who are physically fit, according to research in the International Journal of Epidemiology.
In an observational study of more than 1.3 million Swedish men spanning nearly 30 years, researchers also found that young men at the highest aerobic fitness level (> 320 W) had a reduced risk for death from any cause and, in particular, for death associated with alcohol and drug abuse.
“It seems more important to be of normal weight at 18 years of age than being fit,”
Peter Nordstr ö m, PhD, professor and chief physician in the department of community medicine and rehabilitation, geriatric medicine at Umea University, Sweden, told Endocrine Today. “What we found was that those who were obese and in the top 25% of fitness had about a 30% higher risk of death during follow-up than those who were normal weight and in the lowest 25% of fitness.”
Nordstrom and colleagues analyzed data from 1,317,713 Swedish men participating in the mandatory Swedish military conscription from 1969 to 1996 (mean age at conscription, 18.3 years). Men completed an electronically braked ergometer cycle test at baseline to assess aerobic fitness; researchers calculated weight-adjusted aerobic fitness by dividing each participant’s tests results by his body weight. Researchers followed participants until date of death (using data from the National Cause of Death Registry), emigration or Dec. 31, 2012.
During a mean follow-up period of 28.8 years, 44,301 participants died; the most common causes of death were trauma (n = 10,661), cancer (n = 8,566), cardiovascular disease (n = 7,695) and suicide (n = 4,619). For men with aerobic fitness below the mean of 274 W, the risk for death from any cause increased, according to researchers; after adjusting for age and year of conscription, men in the highest fifth of aerobic fitness had a 51% lower risk for death from any cause vs. men in the lowest fifth (HR = 0.49; 95% CI, 0.47-0.51).
Researchers found that normal-weight men (BMI 18.5-25 kg/m²) in all quartiles of aerobic fitness were at a lower risk for death from any cause compared with men with obesity (BMI > 30 kg/m²). After adjusting for age and year of conscription, normal-weight men in the upper half of aerobic fitness range had a 34% lower risk for death then men in the lower half (HR = 0.66; 95% CI, 0.64-0.68). In men with overweight, risk fell to 28%; in men with grade I obesity, risk fell to 26%. Researchers found no association between all-cause death and aerobic fitness in men with grades 2 and 3 obesity.
“These results counter the notion that the ‘fat but fit’ condition does not increase mortality risk,” the researchers wrote. “Despite the limitation posed by the observational nature of this study, these results suggest that low BMI early in life is more important than high physical fitness, with regard to reducing the risk of early death.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Caroline Apovian, MD, FACP, FACN
This study looked at more than 1.3 million Swedish men conscripted between 1969 and 1996 and evaluated the relationship between aerobic fitness and BMI in late adolescence and mortality in addition to whether a high fitness level can compensate for the risk of death from obesity. Fitness level was determined by ergometer cycle testing. Results showed that those in the highest fifth of aerobic fitness were at lower risk for death from any cause that those in the lowest fifth, and the strongest association was seen for death from alcohol and narcotics as opposed to cardiovascular disease. Aerobic fitness was associated with reduced risk for death from any cause in normal-weight and overweight subjects, but the benefits were reduced in obese subjects. Unfit normal-weight individuals had a 30% lower risk for death from any cause than fit obese individuals. The most notable finding in this study was that it is better for longevity to be unfit and normal weight than to be fit and obese. This may help settle the controversy about "fat but fit," and the claims that fitness compensates for obesity, which runs counter to what this study suggests.
The strengths of this study are that it evaluated more than 1.3 million young men, and that the fitness evaluation was dynamic by bike ergometry. One of the limitations of this study is that obesity was measured by BMI only and not by percent body fat. However, the lack of compensation of fitness for BMI was still strong. Another strong limitation was lack of control for smoking. This is likely significant as there were more smokers, most likely in the earlier years than later, which may have confounded results by time. However, as is the case with how body fat was estimated, smokers usually are of lower BMI and would have more untimely deaths than nonsmokers and would skew results toward benefit for the “fat but fit.”
This study shows that low aerobic fitness in late adolescence is a predictor of early death. It also suggests that fitness is not fully protective of early death in those who are obese. The study supports the notion that for longevity it is important to be fit and lean.
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