US weight guidelines: is it also important to consider cardiorespiratory fitness?

The health consequences of weight ranges across low to moderate and high levels of cardiorespiratory fitness are unknown.

To evaluate the validity of the 1995 US weight guidelines, while considering cardiorespiratory fitness.

We followed 21,856 men, aged 30-83 y, who had a complete preventive medical examination, including a maximal treadmill exercise test and body composition assessment. There were 427 deaths (144 cardiovascular disease (CVD); 143 cancer; 140 others) during an average of 8.1 y of follow-up. We used Cox proportional hazards regression to examine the relations among cardiorespiratory fitness, body mass index (BMI, kg/m2), and all-cause and CVD mortality.

After adjustment for age, examination year, cigarette smoking and alcohol intake, we observed that men with a BMI of 19.0 to < 25.0 and who were unfit had 2.3 times the risk of all-cause mortality (95% confidence interval (95% CI), 1.59-3.17, P < 0.001) compared with fit men in this BMI group (reference category). Unfit men with a BMI of 25.0 to < 27.8 also had a greater risk of all-cause mortality than fit men in the same BMI category. Fit but overweight men (BMI > or = 27.8) had a similar rate of all-cause mortality as physically fit men of normal weight (BMI 19.0 to < 25.0) and had a lower risk of all-cause mortality than unfit and normal weight men. Fit men of normal weight had the lowest CVD mortality, while unfit and overweight men experienced the highest CVD mortality. Unfit men had substantially higher CVD mortality than fit men in each BMI group.

Unfit men had higher all-cause and CVD mortality than fit men. The health benefits of normal weights appear to be limited to men who have moderate or high levels of cardiorespiratory fitness. These data suggest that the 1995 US weight guidelines may be misleading unless cardiorespiratory fitness is taken into account.