After a run, you want to feel exhilarated, strong, confident—not bloated. But looking like you suddenly gained 10 pounds instead of burning a bunch of calories while logging a few miles isn’t uncommon. So what’s going on?
'When people say they feel bloated, mostly what they feel is not food but air,' says Daniel Freedberg, M.D., a gastroenterologist and Assistant Professor of Medicine at Columbia University Medical Center. 'Usually, it's air in the colon, which is kind of a storage unit that can be decompressed like a balloon; it can be flat and almost nothing, or it can be all full of air and really big in volume. And when it’s big and full of air, people feel bloated and uncomfortable.'
When you’re running, you’re likely breathing heavily, gulping down air. But 'instead of going into our lungs, some of that air goes down our oesophagus and then into our stomach and eventually into our intestines and colons,' explains Freedburg. 'A small percent of it can be absorbed across the wall of the intestine, but most of it has to come out and it does so via flatulence.'
But running also puts your body in a stressful state where your fight-or-flight response is engaged—so it’s not exactly the best time for your bowels to be doing anything. (Ahem, never trust a fart after mile nine.) 'The GI tract tends to slow down, and it's not going to move that air through as well,' says Freedburg. That’s going to cause it to build up in your lower abdomen; hence, bloating.
And because exercise acts as a stressor, it triggers your adrenal gland to release the stress hormone cortisol. 'We secrete cortisol in times of stress—for example, a hard run or a stressful job will both increase cortisol levels,' says Tiffany Chag, R.D., C.S.C.S., a sports performance specialist and sports dietitian at the Hospital for Special Surgery in New York City.
That spike in cortisol caused by exercise promotes the production of glucose by the liver for ready-to-use energy, the breakdown of muscle protein into amino acids that are then converted to glucose for energy, and the secretion of glucose into the bloodstream for ready-to-use energy, Chag explains. All good things during a workout! But 'chronically elevated levels of cortisol can lead to chronically elevated blood pressure, which can then lead to fluid retention,' she adds. When your body’s hanging on to extra water, it can make you feel and look heavier, or bloated.
How to avoid feeling bloated when you run
What you eat before or during a run has an even bigger role on how you feel throughout it. 'When you’re running, blood is diverted away from the gut and into the working muscles,' explains Natalie Rizzo, R.D., author of The No-Brainer Nutrition Guide for Every Runner. 'If you eat a large meal shortly before a run, chances are the food is going to sit undigested in your stomach and cause distress.' The same can happen if you eat fatty foods, because they take a long time to digest, or sugary drinks and high-fibre foods, which can both cause bloating and gas when consumed too close to a run.
New runners are especially susceptible to a distended stomach, says Rizzo. 'The stomach is a muscle and needs to be trained in how to handle the up and down motion of running,' she says. Longer distance or more experienced runners aren’t immune, though. 'People who haven’t figured out their sports nutrition yet will probably have issues, and those who rely on a lot of sports products may have some bloating until their body gets used to the products.'
To avoid that puffed up feeling during or after a run, nailing your fuel strategy is key. 'Don’t overload yourself with fatty foods, fibre, or sugary drinks before a run. Simple carbs like fruit or starches are considered easy to digest pre-run fuel,' says Rizzo. 'Listen to your stomach and pay attention to certain foods that may not agree with it. And, most importantly, stay hydrated throughout the day!'
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