Experts weigh in on the trendy approach, which is said to help avoid jet lag and GI distress after long-haul travel.
Fasting is definitely buzzy right now. Intermittent fasting is becoming increasingly popular in the fitness community as a way to lose weight, and now, influencers are talking about other ways they use fasting as a tool for better health. (FWIW, some experts say the potential benefits of intermittent fasting may not be worth the risks.)
One of the primary ways people are incorporating fasting into their routines is during air travel as a way to decrease both jet lag and gastrointestinal symptoms sometimes associated with flying. (Influencer Lee Tilghman, for example, used the approach and sang its praises on a recent trip to Europe.) But is the cure for jet lag really to simply not eat on a flight that crosses time zones? And can skipping food really help travel-related stomach issues? Here's what experts have to say.
As it turns out, the idea of fasting during travel isn't so *new* at all. "Although intermittent fasting is more recently gaining popularity, international travelers from the Army, CIA, and Navy actually used it as early as the 1980s," says Nancy Rahnama, M.D., a bariatric physician. While doing research on the circadian rhythm, a.k.a. the body's biological clock, biologists discovered that when the rhythm is altered by differing hours of daylight (i.e. changing time zones) or meal timing, the body will fail to perform at its best, explains Dr. Rahnama. They came up with a protocol to help reset someone's circadian rhythm when traveling and it involves—you guessed it—fasting while in transit.
"It has been suggested that by fasting, the body's internal clock is allowed to reset and turn back on with breakfast at the destination's first meal. "This may help decrease the effects of jet lag, increase energy, and avoid disruptions in metabolism associated with flying," says Dr. Rahnama.
As for the digestive piece, it's quite common to have digestive issues in the dry, high-altitude environment in the air. "Studies on flight crew members have illustrated that with the decrease in air pressure, there is an associated slowing of gastric motility and delay of digestion," says Dr. Rahnama. "By fasting, the gut will be relieved of its duties and the associated symptoms—like gastric reflux and bloating—may be avoided."
Does It Work?
In short, probably—especially on the jet lag front, but only under specific circumstances. "There is plentiful support in scientific literature to suggest that meal timing influences our biological circadian rhythm, which is at the core of the experience of jet lag," says registered dietitian Hannah Meier. (In fact, there are other ways to cure jet lag with food that also involve meal timing.)
But here's where things get specific: "If you are flying overnight and land in the morning in time for breakfast, fasting on the flight may help reduce jet lag if you are able to sleep and can transition your circadian rhythm to match that of your destination by starting your day with a morning meal, paralleling an overnight fast followed by breakfast," says Meier. But it's important to note that this will only work if you're able to mimic an overnight fast and then eat breakfast at the correct time for your new time zone when you land.
Plus, there are other ways to avoid jet-lag that don't necessarily involve fasting. "Studies show that the circadian rhythm is most sensitive to light exposure," says Dr. Rahnama. "By wearing an eye mask and sleeping at the bedtime of your destination during your flight, you'll have the greatest benefits." (Taking melatonin, the hormone secreted by your body's internal clock, at the time of your destination's bedtime can help with this.) In other words, you may be able to eat before you sleep and when you wake up and reap the same jet-lag benefits from fasting, as long as your timing is right.
In terms of digestive issues, while studies do show that food eaten during a flight may not be digested properly due to altitude, it's worth mentioning that there are also other options in this arena. "Avoiding high fiber foods can significantly decrease the effects of altitude on digestion during a flight," says Dr. Rahnama. She also recommends opting for foods that are easier to digest to decrease unpleasant side effects and bringing your own food from home that you know your stomach can handle. (Related: I Put These Healthy Travel Tips to the Test While Traveling Across the Globe)
However, there's also a potential downside to fasting in the stomach arena. "Fasting will slow your GI tract, which means waste will move more slowly through your digestive tract," says registered dietitian Suzanne Dixon. Bottom line: If you're worried about constipation, fasting is not likely to help.
People Who Shouldn't Fast
There are some people who shouldn't fast—period. For starters, some people simply don't like it or don't feel well when fasting. "Many people cannot go long periods of time without eating," says Dr. Rahnama. "Symptoms of low blood sugar may be more likely in some than others. If you have symptoms of weakness, shakiness, brain fog, or lightheadedness, then you should make sure you are adequately hydrated and have something to eat." If you take medication that requires a full stomach or have diabetes, fasting is no-go for you as well, says Dr. Rahnama.
Fasting also may cause a spike in cortisol, says Dr. Rahnama, which could make you feel anxious during the flight. If this happens to you, don't force it and have something to eat.
People who get motion sickness in the air may also find that fasting makes them feel worse. "Having a completely empty stomach can worsen nausea for some people," says Suzanne Dixon, a registered dietitian and epidemiologist.
Lastly, if you have a history with disordered eating, Meier recommends skipping fasting in any context. "If taken too far, chronic energy restriction can lower metabolic rate and increase fixation with food and other eating disorder behaviors." Restriction can also lead to compensatory behaviors like binge eating in many people, as our bodies are designed for survival and will use any means necessary to obtain nutrients when we are starved of them, she says.
Tips for Trying It
If you do want to give fasting in the air a try, here's what you need to know. Traditionally, this approach recommends fasting for 12 to 16 hours, leading up to and including the time of your flight and ending with breakfast in your destination's time zone, although experts say that it's not entirely necessary to fast for that long to see benefits. "If choosing to fast during a flight, there is no need to extend the fast longer than eight hours during your flight to reap the benefits," Meier says.
She suggests eating a healthy, balanced snack before boarding the plane and something similar to your favorite breakfast upon landing, "which will help signal to your body's internal clock that it is 'morning' where you are." And since fasting really only works for jet lag if you're flying overnight, Meier recommends simply sticking to a normal routine of eating every three to four hours if you're traveling during daytime hours.
And of course, don't forget to hydrate. Drinking plenty of water in-flight is crucial whether you choose to fast or not. Hydration and sleep should be prioritized just as much, if not more, than meal timing alone, according to Meier.
It's also a good idea to do a test run if you're new to fasting. "If you've never tried going for more than a few hours without food during the day (and many people haven't), you may want to practice at home first, before deploying this method for the first time while traveling," Dixon says. After all, the logistics of travel can be anxiety-inducing already, so it's best to minimize the potential for extra stress by being prepared.