Feeling nauseous when hungry is generally due to a build up of stomach acids or a drop in brain blood pressure and oxygen levels. This problem is usually due to poor function of the stomach and intestinal tract.
The stomach constantly produces stomach acids. These acids are produced to help digest food, kill harmful bacteria and activate digestive enzymes. After eating a meal, the stomach produces more acids than normal and sometimes the excess causes a feeling of sickness in between meals.
The intestinal tract is designed to push any content within forward and this motion goes on throughout the day. The esophagus pushes food into the stomach and the stomach pushes partially digested food and stomach acid into the small intestine. The small intestine absorbs the necessary nutrients from the food and then pushes the waste to the colon where it is then passed through the rectum.
The autonomic nervous system controls the intestinal tract performance, and any dysfunction within the system can create a backup of stomach acids. When the movement of contents from the stomach is slowed, a feeling of hunger is common and often followed by a feeling of nausea. An excessive build up of stomach acid is known as dyspepsia and is commonly mistaken for heartburn.