What causes belching? 

The ability to belch is almost universal. Belching, also known as  burping (medically referred to as eructation), is the act of expelling gas from the stomach out  through the mouth. The usual cause of belching is a distended (inflated) stomach caused by swallowed air. The distention of the stomach causes abdominal discomfort, and the belching expels the air and relieves the discomfort. The common reasons for swallowing large amounts of air (aerophagia) are gulping food or drink  too rapidly, anxiety, and carbonated beverages. People are often unaware that  they are swallowing air. "Burping" infants during bottle or breastfeeding is important in order  to expel air in the stomach that has been swallowed with the formula or milk. 

Excessive air in the stomach is not the only cause of belching. For some people, belching becomes  a habit and does not reflect the amount of air in their stomachs. For others, belching is  a response to any type of abdominal discomfort and not just to discomfort due to increased gas. Everyone knows that when they have mild abdominal discomfort, belching often relieves the problem. This is because excessive air in the stomach often is the cause of mild abdominal discomfort. As a result, people belch whenever mild abdominal discomfort is felt regardless of its cause. 

Belching is not the simple act that many people think it is. Belching requires the coordination of several activities. 

• The larynx must be closed-off so that any liquid or food that might return with the air from the stomach won't get into the lungs. 
• This  is accomplished by voluntarily raising the larynx as is done when swallowing. 
• Raising the larynx also relaxes the upper esophageal sphincter so that air can pass more easily from the esophagus into the throat. 
• The lower esophageal sphincter must open so that air can pass from the stomach into the esophagus. 
• While all this is occurring, the diaphragm descends just as it does when a breath is taken. 
• This increases abdominal pressure  and decreases pressure in the chest. 
• The changes in pressure promote the flow  of air  from the stomach  in the abdomen to the esophagus in the chest. 

• Bloating is the subjective sensation (feeling) that the abdomen is larger than normal. Thus, bloating is a symptom akin to the symptom of discomfort. 
• In contrast, distention is the objective determination (physical finding) that the abdomen is larger than normal. Distention  can be determined by such observations as the inability to fit into clothes or looking down at the stomach  and noting that it is clearly larger than normal. 

In some instances, bloating may represent a mild form of distention since the abdomen does not become physically (visibly or measurably) enlarged until its volume increases by one quart. Nevertheless, bloating should never be assumed to be the same as distention. Bloating and even very mild cases of distention may be caused by relaxation of the muscles of the abdominal wall. 

There are three  ways in which abdominal distention can arise. The causes are an increase in air, fluid, or tissue within the abdomen. The diseases or conditions that cause an increase of any of these three factors are very different from one anther. Therefore, it is important  to determine which of them is distending the abdomen. 

There are two types of distention; continuous  and intermittent. 

• Continuous distention  may be caused by the enlargement of an intra-abdominal (within the abdomen) organ, an intra-abdominal tumor, a collection of fluid around the intra-abdominal organs (ascites), or just plain obesity. 
• Intermittent distention  is usually due to the occasional accumulation of gas and/or fluid within the stomach, small intestine, or colon. 

What causes flatulence? 

Flatulence, also known as farting, is the act of passing intestinal gas from the anus.  Gas in the gastrointestinal tract has only two sources. It is either swallowed  air or is produced by bacteria  that normally inhabit  the intestines, primarily the colon. Swallowed air is rarely the cause  of excessive flatulence. 

The usual source is the production of excessive gas  by intestinal bacteria. The  bacteria produce the gas (hydrogen and/or methane) when they digest foods, primarily sugars and polysaccharides (for example, starch, cellulose), that have not been digested during passage through the small  intestine. (The bacteria also produce carbon dioxide, but the carbon dioxide is so rapidly absorbed from the intestine that very little passes in flatus.) 

Sugars 

Sugars that are commonly poorly digested (maldigested) and malabsorbed are lactose, sorbitol, and fructose. 

Lactose is the sugar in milk. The absence of the enzyme lactase in the lining of the intestines, which is a genetic trait, causes the maldigestion. Lactase is important because it breaks apart the lactose so that it can be absorbed. 
Sorbitol is a commonly used sweetener in low calorie foods. 
Fructose is a commonly used sweetener in all types of candies and drinks. 

Starches 

Starches are another common source of intestinal  gas. Starches are polysaccharides  that are produced by plants and are composed of long chains of sugars, primarily fructose. Common sources of different types of starch include wheat, oats, potatoes, corn, and rice. 

• Rice is the most easily digested starch and little undigested rice starch reaches the colon and the colonic bacteria. Accordingly, the consumption of rice produces little gas. 
• In contrast, some of the starches  in wheat, oats, potatoes, and, to a lesser extent, corn, all  may reach the colon. These starches, therefore, may result in the production of appreciable amounts of gas. 
• The starch in whole grains produces more  gas than the starch  in refined (purified) grains. Thus, more gas is formed after eating foods made with whole wheat flour than with refined wheat flour. This difference in gas production probably occurs because  of the fiber (similar to a complex starch) present in the whole grain flour. Much of this fiber is removed during the processing of whole grains into refined flour. 
• Finally, certain fruits  and vegetables, for example, cabbage, also contain poorly digested starches that reach the colon  and result in  the formation of gas. 
• Most vegetables and fruits contain cellulose, another type of polysaccharide that is not digested at all as it passes through the small intestine. However, unlike sugars and other starches, cellulose is used only very slowly by colonic bacteria. Therefore, the production of gas after the consumption of fruits and vegetables usually is not great unless the fruits and vegetables also contain sugars or polysaccharides other than cellulose. 

Small amounts of  air are continuously being swallowed and bacteria are constantly producing  gas. Contractions of the intestinal muscles normally propel the gas through the intestines and cause the gas to be expelled. Flatulence (passing intestinal gas) prevents gas from accumulating in the intestines. 

However, there are two other ways in which gas can escape the intestine. 

• First, it can be absorbed across the lining of the intestine into the blood. The gas then travels in the blood and ultimately is excreted in the breath. 
• Second, gas can be removed and used by certain types of bacteria within the intestine. In fact, most of the gas that is formed by bacteria in the intestines is removed by other bacteria in the intestines. (Thank goodness!) 

What are the causes of intermittent abdominal bloating/distention? 

Excessive production of gas%3