What some people are not aware of is that the esophagus traverses the diaphragm – a powerful muscle that draws air into your lungs. Recent studies suggest that the way you use your diaphragm while breathing affects the LES. For example, research published in the Gastroenterology journal concluded that a diaphragm that was too tight caused the LES to relax too much, thus making it less effective.
What belly breathing does is it helps the abdomen expand and allows your diaphragm to move more and tighten around your lungs, so you let more air out when you exhale. The effect is the same in the opposite direction – belly breathing also allows the diaphragm to expand deeper into the belly area, which helps you inhale more.
This means that by practicing belly breathing, you can help maintain the proper functioning of the LES, preventing heartburn in the long term and dealing with the symptoms of the condition in the short term.