1. How Air Gets Into Your Stomach When You Swallow
You do not only swallow air when eating a meal. Air enters your stomach when you drink water or swallow saliva. According to research, the amount of air swallowed with each single gulp is estimated to be between 8 and 32 mL [2]. To visualize this, a teaspoon holds about 5 mL, so each swallow brings in roughly one and a half to six teaspoons of air. This is an estimate per swallow, not a daily total, and the amount varies from person to person and situation to situation.
Where does this swallowed air go? The MSD Manual Home Edition states that most of the air you swallow is later released as a burp. Only a very small amount moves further down into the digestive tract [1]. Gas from carbonated drinks is also one of the causes of burping [1]. So, how does the body push this air out of the stomach?
2. How a Stretched Stomach Opens the Muscle Ring Between Stomach and Esophagus
At the boundary between the esophagus and the stomach, there is a ring of muscle that is usually closed. This is called the lower esophageal sphincter. When the upper part of the stomach stretches as it fills with air, this muscle temporarily relaxes. Researchers call this a transient relaxation of the lower esophageal sphincter [3]. Through this gap, the air in the stomach moves back up into the esophagus. This movement is what we recognize as a normal burp [3].
Once the air moves up into the esophagus, the esophagus expands. This expansion causes another muscle at the bottom of the throat, the upper esophageal sphincter, to relax as well. This allows the air to exit the body [4]. Imagine the exit on the stomach side opening first, followed by the exit on the throat side. Reading this, you might feel like you are opening these valves yourself when you decide to burp. But is that really true?
3. How an Automatic Reflex in the Brainstem Triggers a Burp
When the upper part of the stomach stretches, a signal is sent to the brainstem, which is deep inside the brain. This signal travels through the vagus nerve, a long nerve in the body. From the brainstem, a command is sent back through the vagus nerve to relax the muscle at the boundary of the esophagus and stomach. Substances such as nitric oxide are involved in this process [3].
This means the trigger for a burp is the stretching of the stomach by the air inside it. Even though the brain sends the command, you are not thinking about it or deciding to do it. It is an automatic reflex that passes through the brainstem. Normal burps that release air from the stomach are not things you initiate yourself [3]. When the stomach expands, signals travel from the brainstem to the muscles, and the air escapes. Burping happens through this reflex. But is this movement, which happens every day, something unusual for the body?
4. Why Burping Is Normal Even in Healthy People
It has been reported that even healthy people without any symptoms experience a small number of gastric burps [3]. The fact that burping occurs is not abnormal in itself.
There is a different behavior called "supragastric belching." This is when a person sucks air in from the mouth into the esophagus or pushes it in, and then immediately releases it from the throat. This does not involve the stomach. It is considered to have strong behavioral and psychological aspects, and it is different from normal burps that release air from the stomach [3]. This article focuses on normal burps. So, if gas enters the body from sources other than swallowed air, such as carbonated drinks, does burping increase?
5. Why Carbonated Drinks Were Not Linked to Burping Disorders in One Osaka Survey
A research team from Osaka Metropolitan University conducted a web survey of approximately 10,000 adults. They looked for people who had a condition where burping was troublesome, known as a burping disorder. Only 151 people (1.5%) met the criteria. The results were published in the American Journal of Gastroenterology in July 2024 [5].
The study found that burping disorders were linked to having digestive diseases, eating until full, and having chewing either too little or too much (either too few or too many). However, frequently drinking carbonated drinks was not linked to burping disorders [5]. It is important to note that this survey investigated "burping disorders" that were frequent enough to cause trouble. It did not measure the number of normal burps or the amount of gas produced by carbonated drinks. The fact that gas from carbonated drinks causes burping is mentioned in other materials [1]. Burping is also an important topic for babies. How is burping viewed after breastfeeding?
6. Do Babies Need to Burp After Feeding?
Babies swallow air along with milk during feeding. Therefore, it is often suggested that parents should help babies burp after feeding. However, there are individual differences. The Kyoto Prefecture parenting Q&A states that if a baby does not burp after a while but is in a good mood, you do not need to force them to burp [6]. It also says that if the baby falls asleep, there is no need to wake them up just to make them burp [6]. As we have seen, burping is a mechanism where the body automatically works to release air. The advice that you do not need to force a burp if the baby is happy and has not burped after waiting aligns with this understanding of the body’s automatic functions.
7. How You Can Investigate Your Own Burping at Home
Something you can do today is to pay attention to whether you feel like you are about to burp before it happens, or if it happens without you noticing. You can notice whether a burp feels like something you choose or happens on its own. For official information, the "Gas" section of the MSD Manual Home Edition is available in Japanese. Research news from Osaka Metropolitan University and the Kyoto Prefecture parenting Q&A are also useful references. Please note that this article is not medical advice. If you are troubled by burping or stomach discomfort, please consult a doctor.