Originally appeared in the article, "I’m a Gastroenterologist, and This Is the Best (and Worst) Sleep Position for Smooth Digestion’" by Michele Ross in Well + Good on September 28, 2022.

If you’re on a mission to improve your digestion, let me clue you in on a little secret: It’s not just what you eat, but how you eat that matters. For instance, eating while standing up versus sitting down can play a role in the way your stomach feels following a meal. Countless other lifestyle factors also come into play in this regard. (If you’ve ever dealt with intense episodes of stress, I’m sure you already know that the gut-brain connection is very real.)

On the topic of digestion after dark, have you ever wondered if—and how—your sleep position affects digestion? Same. In search of answers, we reached out to Ali Rezaie, MD, a gastroenterologist at Cedars-Sinai in Los Angeles, author of The Microbiome Connection and co-founder of The Good LFE.

How your sleep position impacts digestion

We already know that lying down after eating and eating a big meal very close to bedtime can tamper with sleep and digestion for some folks. Moreover, since whole gut transit time (i.e., the period from when you eat your food to when it exits your body) can take up to 73 hours or longer, it’s clear that your digestive system is still at work before, during, and after you get your shut-eye. And if you struggle with certain digestive issues, gut health experts say that it's certainly worth taking a closer look at your sleeping position to see how it may help or exacerbate symptoms.

“For starters, multiple studies have shown that sleeping on the right lateral position increases acid reflux episodes and heartburn as compared to the left lateral position,” Dr. Rezaie says. “This is thought to be due to positioning of the stomach, which lays above the distal part of the esophagus when sleeping on the right side.” In addition, he notes that the position of your noggin while sleeping can also influence digestive function, stating that “elevation of the head of the bed has been associated with less reflux episodes.”

Is it always better to sleep on your left side to support digestion?

With Dr. Rezaie’s insights in mind, you be making a mental note to switch your sleeping position tonight—but he takes care to mention that this change won’t necessarily benefit everyone across the board. “If you do not suffer from reflux, there does not appear to be any advantage of forcing yourself to sleep on the left side,” Dr. Rezaie says. On top of that, he even notes that one small study on healthy volunteers showed that the right lateral position turned out to be better for stomach emptying, though further research is needed to support this finding conclusively.

However, if you do happen to struggle with acid reflux (GERD), you’ll want to heed his advice. “We generally recommend for patients with GERD to sleep on their left side and elevate their head of the bed by one or two inches,” Dr. Rezaie says, as doing so can help decrease one's number of acid reflux episodes and may also alleviate discomfort.

Another word to the wise: Before you start to stack up your pillows, Dr. Rezaie says that this isn’t the best course of action. “Using extra regular pillows is not the same as elevation of the head of the bed, as the chest does not rise with that strategy,” he explains. He continues to say that it may actually end up placing excess pressure on the cervical spine. Instead, your best bet in this case would be to shop for a wedge pillow that’s specifically designed to help with GERD.

Are there certain sleeping positions that are generally not good for digestion?

So far, we’ve covered sleeping on your left side and your right side—but how will your digestion fare if you sleep on your stomach or back, or switch from one position to the next? “While there is not much good evidence, anecdotally, sleeping prone [facing downward on your stomach] is not considered ideal for digestion,” Dr. Rezaie says. To the layman, this makes sense since it can potentially cause excess pressure on your stomach—and anyone who’s ever needed to undo a button on their jeans after a meal knows that physical constriction can be uncomfortable, to say the least.

As for how else to improve your digestive function when it comes to your sleeping position of choice? Above all, clocking in enough ZZZ’s is key. “The best for your digestion is to get a good amount of sleep, irrespective of being in a lateral position or your back,” Dr. Rezaie says.

The bottom line

While people with acid reflux are likely to experience relief by taking care to sleep on their left side and with their head elevated with a wedge pillow, everyone else can—pun intended—rest assured that, in most cases, their preferred sleeping position won’t cause digestive distress. With that said, you can adopt other habits that are sure to keep your GI tract happy and healthy all night long.

For starters, Dr. Rezaie recommends avoiding eating a heavy meal three to four hours prior to hitting the hay in order to keep the fasting movements of the intestines in check. (One study in the American Journal of Gastroenterology found that the higher end of this window significantly reduces symptoms in patients with GERD.) Similarly, he advises not eating a meal in the middle of the night. “These movements of the small bowel are integral for our bowel function and the balance of the gut microbiome, though there does not appear to be a preferred sleeping position for these waves,” Dr. Rezaie shares. However, he concludes, abstaining from eating in the wee hours of the night “is especially important for those who suffer from bloating, IBS, or SIBO.”