People come to running with many different goals: to compete, to hang out with friends, to get healthier, to “lean out.” This sport can help you achieve many of these things.
However, according to a recent study published in BMJ Open Sport and Exercise Medicine, running on its own probably won’t accomplish that last one. Running your way to shredded quads or chiseled abs will likely mean you’re chasing miles for a while with no result.
The Scientific Debate About Body Composition
It’s an open scientific debate as to whether exercise alone can improve body composition. While some research says yes, other studies say “not really.” What most of these studies seem to agree on is the idea that exercise, especially high-intensity exercise like running, can reduce visceral adipose tissue (VAT).
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VAT is fat that surrounds your organs and is a major risk factor for cardiometabolic disease, like diabetes or heart disease, so reducing it can give you better odds of staying healthy and living longer.
A New Research Approach to Understanding Exercise and Body Composition
Two shortcomings of most studies investigating the effects of physical activity on body composition arise from their design: They’re observational, which introduces both reliability issues (did the subjects accurately report their exercise?) and confounding factors (people who run more might also partake in other healthy habits, which would affect their body composition). Also, most of these studies look at overweight or obese populations, which is important for public health research but isn’t the reality of everyone trying to improve their body composition.
To improve upon these limitations, a team of researchers from The University of Arizona, George Washington University, and University of Southern California took another approach: They employed a method called Mendelian randomization. This method uses genetic variations (rather than observed or self-reported data) as inputs or “proxies” for a behavior in order to examine whether that behavior causes an outcome.
“We wanted to look at the human experience of how physical activity influences body composition,” Ferris Ramadan, MS, an epidemiologist and data scientist at The University of Arizona and first author on the BMJ Open Sport and Exercise Medicine study told Runner’s World. The behavior being represented by genes in this study was exercise, and the outcome was body composition.
Ramadan and his coauthors began by identifying genes that predict varying levels of physical activity. This is similar to, for example, certain genes predicting that a person will be tall or develop Alzheimer’s. Because genetic differences are inherited randomly, using them as inputs (instead of actual physical activity) lessens the chance that other potential correlating factors, like socioeconomic status or smoking history, may bias the data (eg, if smokers are less active, those individuals may have worse body composition because they smoke, not just because of their low activity level).
Additionally, using a genetic rather than behavioral input avoids the possibility of reverse causation, where it’s someone’s body composition that caused them to engage in greater levels of physical activity.
With the physical activity genes variations in hand, the researchers accessed a biobank of hundreds of thousands of subjects to look for associations between those genes and body composition outcomes like body mass index (BMI), waist circumference, waist-to-hip ratio, VAT , and total body fat percent.
“We found that there’s a negligible effect of physical activity, really at any level, on body composition measures,” said Ramadan.
There was one exception: As prior studies have found, high-intensity physical activity (like running) reduced or protected against VAT. This is great news for runners’ overall health; however, it’s unlikely to yield any visible or easily measurable body composition results.
“For someone who’s thinking ‘oh I want to do spot reduction in my gut,’ it’s not going to work, because this visceral adipose tissue is actually a relatively small proportion of your overall body composition,” said Ramadan.
Factoring Nutrition into Exercise and Body Composition
While exercise alone may not improve body composition, studies do show that combining physical exercise with a nutritional strategy can work. However, this isn’t as simple as “eat less and exercise more.”
Nicole Farnsworth, a registered dietitian who works in the Sports Medicine Division of Boston Children’s Hospital and in private practice at Laura Moretti Nutrition LLC, says that eating too little can, in some cases, backfire. She sees clients arrive at her practice frustrated at having restricted their food intake and increased their exercise, only to see their weight plateau or, in some cases, even increase.
“Many patients who come in to see me may ask ‘How can I not be eating enough? I haven’t lost weight’ or in fact they’ve gained weight, or body mass,” says Farnsworth.
The reason someone might not lose or might even gain weight while exercising more and/or eating less is that energy availability (how many calories you’re taking in versus how many you’re expending) can affect body composition differently in different people. Farnsworth explains that for some people, when they burn more calories than they eat, their bodies are genetically programmed to hold onto fuel and nutrition stores more tightly—leading to weight maintenance or even weight gain.
Furthermore, for any athlete, not taking in enough calories to fuel your workouts will eventually lead to worse performance outcomes. In fact, a body composition that is too low in body fat can lead to a variety of negative health outcomes, including hormonal changes and increased risk for bone stress injuries.
“It’s not thinner is faster, it’s fueled is faster,” says Farnsworth.
She emphasizes that when it comes to performance, most athletes are better off focusing on optimizing their nutrition and training strategies than trying to adjust body composition. “A lot of the time, with most athletes, if the fueling piece and the training piece are the primary focus, that’s going to make the biggest difference,” she says.
The Bottom Line on Exercise and Body Composition
At the end of the day, whether improved body composition or a PR is your running goal, putting in the miles can help you get there. But running isn’t a magic bullet; it won’t work in isolation. Rest, recovery, periodized training, and nutrition are all essential to reach any goal.
Also, even if running doesn’t improve your body composition by itself, it offers a whole lot of other benefits, like improving brain health, protecting your heart, supporting your mental health, and simply boosting your mood. So let all those pay-offs you experience keep you moving and focused on other goals.
Allison Goldstein is a freelance writer and editor who is endlessly fascinated by the scientific “why” of things. When not writing or reading, she can be found running, baking, or petting her cat, Tabouli.
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