Blood Flow
Stress changes blood flow within the body. When the body becomes stressed, it channels more blood to the muscles of the arms and legs, causing less blood to go to the stomach. As a result, food is more slowly digested and instead remains in the stomach for longer periods of time. Undigested food is one of the primary causes of acid reflux as the food pushes up against the top of the stomach, opening a valve called the lower esophageal sphincter. When undigested food causes this sphincter to open, this allows acid to reflux back up from the stomach into the esophagus. This is one way in which increased stress can cause acid reflux.
Eating Habits
Another way in which stress can lead to acid reflux is through alterations in eating habits. People who are experiencing a great deal of psychological stress are more likely to increase their consumption of alcohol as well as to eat more fried and fatty foods---so called comfort foods. They are also more likely to smoke and to have late night "binge eating" sessions. All of these behaviors can cause acid reflux both by increasing the amount of stomach acid that is produced as well as relaxing the lower esophageal sphincter, which can lead to acid reflux.
Digestion
Significant stress causes the body's natural "fight or flight" system to become activated. This causes the body to send signals to the digestive system to slow down so that energy and oxygen are not being used up by the digestive tract. As a result the stomach is deprived of energy and certain enzymes that are necessary for digestion. This causes digestion to be slowed, leading to food remaining in the stomach for long periods of time. As the undigested food lingers in the stomach, it can cause excessive churning of the stomach and lead to indigestion. As a result, acid may splash back up the esophagus, leading to acid reflux.
