Lack of Fitness and Overweight Do Not Always Conflate

Wed, 10 Oct. 2012 - 2:11 a.m. MT
Credit: ARA Staff - American Running Association

A study out of the University of South Carolina called the Aerobics Center Longitudinal Study has once again found that the relationship between body fat and fitness level is not always as clear-cut as it once seemed. Previous research has alluded to a need to distinguish between “fat-and-unfit” and “fat-but-fit” in a populous whose collective waistline continues to grow. 

Now, the Arnold School of Public Health has published results in the journal Circulation that shed further light on this need. Changes in cardiorespiratory fitness and in body mass index (BMI) do not always correlate, and do not equally contribute over the long term to all-cause mortality or to cardiovascular disease (CVD) mortality—at least in men, the new study has found.  

Looking at over 14,000 men with a mean age of 44 years, the researchers first measured fitness (in METs) via a maximal treadmill test. They then calculated subjects’ BMI. Follow-up examinations of fitness and BMI occurred at least twice over six years. Eleven years later, 914 all-cause and 300 CVD deaths had occurred. Surprisingly, hazard ratios for each mortality were found to increase with loss of fitness—not with change in BMI, after adjusting for possible confounders and change in fitness over time.

Men who lost fitness had higher all-cause and CVD death risk regardless of BMI change. Conversely, every one-MET improvement in fitness was associated with a 15-percent lower risk of all-cause mortality, and a 19-percent lower risk of CVD death. The study concluded that preventing age-associated fitness loss is important for longevity, regardless of BMI change. 

The findings are important in a world where overweight and obesity can seem insurmountable and in and of themselves a major psychological, in addition to physical, barrier to exercise. Because metabolic changes make weight gain harder to stave off with age, wellness initiatives that place increased attention on strategies to maintain or improve fitness, rather than simply emphasizing weight loss, may be more encouraging and easier to adopt in the long run.

Nevertheless, the National Institutes of Health estimate that 68 percent of American adults are now overweight. Over one-third (34 percent) of American adults are considered obese. There is no question that this is an alarming number, and that overweight people tend to also routinely be unfit. The silver lining here is mainly for folks who are physically active, but for whatever reason, cannot seem to lose weight.

And the researchers are eager to point out that losing extra weight is important for improving health and life span, because weight loss itself leads to—and also may boost the benefits of—fitness. They suggested that future studies may more clearly define the combined heath effects of reducing excessive weight and improving physical fitness. "It is important to study the combined effects of fitness and BMI on mortality, as both clinical indicators impact the development of health recommendations and policies," they concluded.

 

Circulation, Dec. 6, 2011, http://circ.ahajournals.org/content/124/23/2483.abstract

 

NIH, Overweight and Obesity Prevalence Estimates, July 13, 2011, http://win.niddk.nih.gov/statistics/#overweight

(RUNNING & FITNEWS® November / December 2011 • Volume 29, Number 6)




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