**3. What causes GERD? we do not know**

Since the backflow of gastric contents into the esophagus is harmful, to prevent this to happen, the esophagus is anatomically separated from the stomach by the gastroesophageal barrier that consists of two tough muscular components, the lower esophageal sphincter (LES) and the diaphragm. The LES is the 3–4 cm (in adults) distal portion of the esophagus penetrating the diaphragm through the hiatus and entering the abdominal cavity where it connects to the stomach. The diaphragm keeps the esophagus and the stomach in the thoracic cavity and the abdominal cavity separately. The LES and the diaphragm are anchored to each other by the phrenoesophageal ligament so that these two components contract coordinately to prevent the backflow of the stomach contents into the esophagus. For this reason, anything disturbing the function of the gastroesophageal barrier is a potential cause of GERD.

Over the years, many factors have been evaluated for a possible connection with the disease but no one is singled out. Based on the statistical significance, the top five reasons for GERD occurrence are listed as follows.

1.**Overweight/obesity**. Body weight has been commonly recognized as a major contributor to GERD development. The excessive body fat, especially around the abdominal region, puts constant pressure on the stomach, squeezing the gastric fluid to break the gastroesophageal barrier entering the esophageal lumen frequently, damaging the esophageal lining. According to a meta-analysis [9], GERD was detected in 6.64% of the people with a body mass index (BMI) below 18.5, but in 22.63% of the individuals with a BMI above 30, which is the baseline defined for obesity.

*Introductory Chapter: Do We Really Know GERD? DOI: http://dx.doi.org/10.5772/intechopen.106602*


Other controversial factors are noted in GERD development, including delayed gastric emptying, gastric acid over-secretion, age, gender, and race. Take gastric emptying as an example. For a normal person, the entire process from ingestion to defecation takes about 2–5 days to finish. After a meal, the stomach first relaxes to accommodate the ingested food and then breaks it down by rhythmic churning and grinding motions accompanied by the secretion of acid and digestive enzymes, which takes about 2–4 hours before releasing the food remnants into the small intestine for full digestion and absorption. Several factors can slow down the process, such as overeating,

high-fat meals, low hormone secretion, low physical activity, and gastroparesis. In such cases, the accumulating food in the stomach builds up the intra-gastric pressure to push the gastroesophageal barrier to open, allowing the stomach contents to run into the esophagus instead of going down into the intestine [18, 19]. However, several studies did not find a strong correlation between delayed gastric emptying and GERD occurrence [20–22]. For this reason, using prokinetics to improve gastric motility is not recommended by American College of Gastroenterology (ACG) for GERD relief. Similarly, there are conflicting data about age. Biologically speaking, the gastroesophageal barrier should be like any other part of the body, growing stronger before 40 and getting weaker as the age approaches seniors. However, according to the meta-analysis [9], GERD is found in 8.70% of the people at the age of 18–34 and 14.53% in the age group of 35–59 but comes down after the age of 60.
