So, you just had a good run or a good all-evening skronk fest and you're freaking starving. It's okay to pig out on everything you see, right? You just burned like a million calories. Time to order 12 tacos.
Or not. Maybe you only burned 400 calories, so if you eat 600 calories back, and you're not trying to put weight on, you wasted your run (but not the skronk fest. Those are rarely wasted). Many of us do this. I, for example, recently walked about 85 miles for a fundraiser and gained three pounds in the process. Because I couldn't stop eating lasagna and ice cream the entire time.
Why does this happen? Probably for a few reasons—one being hormones and another being our need to reward ourselves. But the finer details are a little murky.
And of course, that post-exercise spell isn't the only time for several orders of tacos. Google "Why do I get hungry after…" and the top suggestions (in Canada anyway) are "drinking," "working out," and "smoking weed." Then there's the aforementioned old reliable hunger inducer: sex.
Why do we get ravenous after sex, exercise, and sexercise?
"Human appetite is highly responsive to physical activity," says Matt Fitzgerald, sports nutritionist and author of The Endurance Diet. "It's easy to see why this is so from an evolutionary perspective. The more we move, the more food we need to consume to keep our bodies functioning. If increasing activity levels did not stimulate our appetite, we could easily end up malnourished during periods of heavy activity."
In the short term, however, exercise—or high intensity exercise anyway—can actually have the opposite effect. "For the first hour or two after a workout, appetite is suppressed," Fitzgerald says. "This is a lingering effect of appetite suppression that occurs during exercise, when the body shunts blood away from the belly to the working muscles, causing circulating levels of the hunger hormone ghrelin to decrease while leptin, a satiety hormone, increases. The higher the intensity of exercise, the stronger these effects, which is why people tend to be less hungry after high-intensity workouts than after low-intensity workouts."
While that's what happens in the short term, in the long term "people generally eat more when they exercise more," says Kendrin Sonnenville, assistant professor of nutritional sciences at the University of Michigan School of Public Health. "The magnitude of this compensation varies widely from person to person, though, and it's important to keep in mind that for many people this increase in food intake is appropriate and healthy."
Interestingly, she also says that some folks struggle with differentiating between hunger and thirst, and that if you don't properly hydrate during exercise you end up eating when in fact your body is calling out for a drink. You should feel thirst in your mouth and hunger in your stomach, apparently. I think I knew that.
If your hunger is related to physical activity (unlike, say, boozing and getting high), it's likely a got something to do with hormones, which come into play along with your brain and your digestive system.
The other reason we scarf it up, as noted by Sonnenville, is because we figure we deserve it.
"That's the reward system," says Ennette Larson-Meyer, professor of human nutrition at the University of Wyoming. And it's the thing that can cost you. "If you're a well-trained athlete and you work out intensely for an hour and burn off a thousand calories, it's going to be harder to eat back those calories, but if you're just going to the gym and your intensity is low and you work out for 30 minutes then you might only burn 300 calories. But you worked out, so you feel like it's more. You can easily stop and grab something that is 500 or 600 calories." (Also, while you may feel gloriously overexerted after sex, it only burns about 100 calories for men and 76 for women.)
Why does weed and alcohol give us the munchies?
If you're hungry after smoking weed, it could be because the THC has fooled your brain into thinking you're starving, even if you just ate, according to a Yale University School of Medicine study. "Even if you just had dinner and you smoke the pot, all of a sudden these neurons that told you to stop eating become the drivers of hunger," Tamas Horvath, a neuroscientist at the Yale School of Medicine and the lead researcher on the study told NPR.
Getting hungry after drinking, meanwhile, is probably because all the booze makes the food more delicious. If you're a woman anyway. A 2015 study found that "alcohol exposure sensitizes the brain's response to food aromas and increases caloric intake," which explains why crappy fast food is harder to resist at 3 am.
"Drinking may influence the digestive system and gut hormones in a way that could influence appetite, but it also seems that the brain is independently influenced by alcohol acting directly from the bloodstream and impacting certain areas related to ingestion in the brain," says Martin Binks, associate professor of nutritional sciences at Texas Tech University. "This makes some people more sensitive to cues to eat."
After a night of boozing, the siren song of the late-night burrito might try to pull you under. But know that it could actually exacerbate your hangover. "Alcohol consumption can lead to low blood sugar,which can make you feel extra hungry," says New York-based registered dietitian Dara Godfrey. "So you find yourself wanting fried food and fat, and carby things like pizza. But that can make you feel worse in the morning."