Nutritional and metabolic complications of bariatric surgery.

Bariatric surgery is an effective treatment for patients with clinically severe obesity. In addition to significant weight loss, it is also associated with improvements in comorbidities. Unfortunately, bariatric surgery also has the potential to cause a variety of nutritional and metabolic complications. These complications are mostly due to the extensive surgically induced anatomical changes incurred by the patient's gastrointestinal tract, particularly with roux-en-Y gastric bypass and biliopancreatic diversion. Complications associated with vertical banded gastroplasty are mostly due to decreased intake amounts of specific nutrients. Macronutrient deficiencies can include severe protein-calorie malnutrition and fat malabsorption. The most common micronutrient deficiencies are of vitamin B12, iron, calcium, and vitamin D. Other micronutrient deficiencies that can lead to serious complications include thiamine, folate, and the fat-soluble vitamins. Counseling, monitoring, and nutrient and mineral supplementation are essential for the treatment and prevention of nutritional and metabolic complications after bariatric surgery.