Fat But Fit? Study Reveals That Fitness, Not Weight, Predicts Risk Of Early Death

11/20/2013 03:42 pm ET | Updated Nov 25, 2013

When it comes to living a long and healthy life, a meta-analysis of mortality studies finds that being physically active, no matter what your weight, trumps being thin and unfit.

Researchers at Middle Tennessee State University, led by exercise scientist Vaughn Barry, Ph.D., examined 10 past studies that recorded information about participants' body mass indexes and fitness levels. The studies looked at the weight and fitness levels of thousands of participants (the largest one included 21,856 people) and continued to follow up with the participants over several years, ranging from an average of 7.7 years to an average of 16 years.

Barry's team crunched the numbers on those past studies by dividing participants into three weight categories based on BMI: normal weight, overweight and obese. Then they put them into two categories based on their performance on an endurance test (in most studies, this involved running on a treadmill): fit and unfit.

They found that fitness levels, not weight, predicted whether or not a participant had died in the study's intervening years. Unfit people, regardless of their weight, had twice the risk of dying during the study than fit people, and overweight and obese people who were fit had similar mortality risks as fit, normal weight participants. Another way of putting it: thin, unfit people had twice the mortality risk as obese fit people.

The study was recently published in the journal Progress in Cardiovascular Diseases.

The findings are hopeful for people with lifelong weight issues, said Barry in a phone interview with the Huffington Post.

"If you're having trouble losing weight or having trouble maintaining weight loss, just get out there and maintain a regular regiment of physical activity," Barry said. "Your risk of mortality is significantly reduced."

And the amount of activity needed to get the benefits of a lower mortality risk aren't as intensive as people might believe. Barry notes that most of the studies he analyzed tested people's performance on a treadmill for an average of eight to 12 minutes, lending credence to the federal government's recommendation that 150 minutes of physical activity a week, achieved in segments as low as 10 minutes at a time, is enough to get yourself into that "fit" category.

Barry used his own life as example. Although he occasionally cycles or swims, the majority of his physical activity is simple brisk walking. He makes sure to park at the opposite end of his university's campus to force him to walk the 10 minutes to his office. Once he's at the office, he alternates between a standing desk and a stationary bike desk as he reads and responds to emails. Outside of the office, he always tries to nab the furthest parking spot wherever he goes -- if he even decides to drive in the first place.

Barry hopes that his meta-analysis serves as a major wakeup call for slender people who don't prioritize physical activity.

Barry's study also pokes holes in the so-called "Obesity Paradox" -- the finding that overweight people tend to have a lower mortality rate, despite excess fat's association with disease. Jointly assessing both fatness and fitness, which is what Barry's study did, could explain why some overweight people have better mortality outcomes than the lean.

"This seems to reduces the effect the Obesity Paradox, as [fitness] lowers everyone's risk," said Barry.

As with any analysis, there are caveats to Barry's findings. For instance, the vast majority of study participants in the 10 experiments Barry analyzed were men, which could introduce a gender bias into his findings. Secondly, it's far too early for researchers to conclude that being overweight is a surefire way to live longer. More studies and meta-analyses like Barry's need to be done to measure weight and fitness's association with diabetes, cancer and hypertension. And if future studies show that fitness, not weight, predicts outcomes for those diseases, it could lead to a new understanding of what "overweight" means in the first place.

"'Overweight' and 'obese' are just labels put at certain cut points," said Barry. "Maybe in the future these cut points will be reassessed."

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