What is the primary complication of gastric bypass that involves symptoms such as facial flushing and lightheadedness?

The primary complication of gastric bypass that involves symptoms such as facial flushing and lightheadedness is indeed dumping syndrome. This condition occurs when food, especially high in sugar, moves too quickly from the stomach into the small intestine. As a result, the body reacts by releasing insulin rapidly, leading to a drop in blood sugar levels. This can cause symptoms like facial flushing, lightheadedness, nausea, and even fainting.

Dumping syndrome is particularly relevant in patients who have undergone gastric bypass because the normal digestive process is altered, and the stomach receives smaller amounts of food at a much quicker pace. The rapid influx of food into the small intestine can irritate the gut, causing these sudden symptoms after eating.

Other options, while they are complications associated with gastric bypass, do not present with the specific symptoms of facial flushing and lightheadedness. Gastro-gastric fistula refers to an abnormal connection between the stomach and a bypassed portion of the digestive tract, intestinal obstruction typically presents with abdominal pain and vomiting, and malnutrition arises from insufficient nutrient absorption but does not specifically result in the acute symptoms noted. This specificity helps clarify why dumping syndrome is the correct choice for this question.