Why might patients who undergo stomach surgery become malnourished?

Patients who undergo stomach surgery, such as gastric bypass, often experience malnutrition primarily because the surgical procedure typically involves bypassing sections of the small intestine, particularly the duodenum and proximal jejunum. These sections are crucial for the absorption of nutrients. When food bypasses these areas, the body may not effectively absorb essential vitamins, minerals, and other nutrients, leading to deficiencies and malnourishment.

Additionally, the nature of the surgery can alter the physiological processes of digestion. For instance, with a reduced stomach capacity, patients may consume smaller portion sizes, which can contribute to inadequate nutrient intake over time. The altered digestive layout can result in malabsorption issues combined with dietary changes, further exacerbating the risk of malnutrition.

While the other factors mentioned, such as psychological issues and food aversions, can influence eating habits and nutritional status, they are not direct consequences of the surgical changes made to the digestive system and its ability to absorb nutrients. The bypass of vital segments of the intestine is the key reason for the increased risk of malnutrition following such surgeries.