Obesity is a risk factor for GERD both because of its physical effects on the body and because the type of diet that often leads to obesity is generally a diet high in fat content. Obesity, particularly when the person has a large waist circumference, increases the pressure inside the abdominal cavity, which includes the stomach. This, in turn, increases the workload on the lower esophageal sphincter, which is then less likely to be an effective barrier against reflux of stomach acid. As we have seen, a high-fat diet increase the risk of symptomatic GERD. Someone who's obese is more likely to eat foods that are high in fat and to eat larger but fewer meals per day. The strain on the LES combined with the dietary factors means that there is an increased risk of GERD in someone who is obese.
Many women develop heartburn during pregnancy. This occurs for two reasons. First, there is an increase in the pressure on the abdominal cavity as the fetus grows and the uterus enlarges. This pressure changes the anatomy of both the stomach and the gastroesophageal junction, and these physical changes make it easier for acid to reflux into the esophagus. Several studies have shown that LES pressure declines as pregnancy progress, and this low pressure, too, increases the likelihood that acid reflux will occur. Second, levels of both estrogen and progesterone in the blood are elevated during pregnancy; elevated levels of both of these sex hormones cause the LES to relax. Also, high estrogen levels and reflux are closely related.
Weight loss, through either dieting or delivery, usually improves or even eliminates GERD symptoms. Even modest amounts of weight loss in someone who is obese can lead to an improvement of symptoms right from the beginning, perhaps because the person is eating a lower-fat diet. A natural corollary to the effect of weight loss is the effect of weight gain: it can bring about GERD symptoms or make existing symptoms worse.
While we are on the subject of weight loss, we should note that exercise can increase intra-abdominal pressure, which in turn decrease the effectiveness of the lower esophageal sprincter. position changes during exercise may also precipitate reflux. These changes are reversed as soon as the exercise is finished, fortunately.