Key Points

• After bariatric surgery, the main deficiencies involve B vitamins and vitamin D, iron, and zinc.
• Risks vary by type of surgery, the presence of malabsorption, and individual factors.
• Attention must be paid to vitamin B₁, whose deficiency can cause potentially irreversible complications.

In France, more than 370,000 adults underwent bariatric surgery between 2007 and 2020. These procedures expose patients to a postoperative nutritional deficiency and, in the most severe cases, malnutrition. These complications result from surgical anatomical changes, which can cause impaired digestion, malabsorption, and neurohormonal alterations; in some patients, harmful behavioral factors (eg, poor food choices and poor adherence to postoperative recommendations) also contribute.

Surgery-Specific Risks

The deficiencies most often reported in studies are vitamin D, folate, vitamin B₁₂, iron, and zinc. Vitamin B₁ deficiencies are rare but carry potentially serious risks. These deficiencies are common to all types of bariatric surgery. With bypass-type procedures such as Roux-en-Y gastric bypass and biliopancreatic diversion with duodenal switch, the risk for deficiency is greater for vitamins A and D, copper, and zinc. However, reduced oral intake and poor tolerance of certain food groups can increase the risk for micronutrient deficiencies regardless of the type of surgery.

Factors that contribute to nutritional deficiencies are as follows:

• Preoperative nutritional deficiencies
• Food intolerances
• Reduced intake or noncompliance with nutritional recommendations
• Weight loss of more than 10% within 1 month is a sign of malnutrition
• Postoperative digestive complications (eg, fistulas or other gastrointestinal disorders) or malabsorption

Obesity itself is associated with micronutrient deficiencies even before surgery because adipose tissue can contribute to storage of fat-soluble vitamins. Chronic inflammation associated with obesity increases hepcidin and thereby limits iron absorption. Furthermore, other metabolic risks can appear after surgery: For example, postprandial hyperinsulinemic hypoglycemia may develop 1-3 years after surgery due to exaggerated insulin and GLP-1 peaks.

Finally, fat malabsorption can lead to an increased risk for calcium oxalate kidney stones, while the development of small intestinal bacterial overgrowth is promoted and can worsen malabsorption and induce liver disease.

Symptoms to Identify

In 2022, the French National Authority for Health reiterated the full range of nutritional complications secondary to bariatric surgery in its guidance on the management of second- and third-line adult obesity. These guidelines include a list of the many clinical features that can point clinicians to a possible deficiency before any laboratory workup: changes in the skin, mucous membranes, and appendages; ocular manifestations; and musculoskeletal, neurologic, hematologic, cardiac, and sexual symptoms. Neurologic complications, though less common, warrant close monitoring because they are certainly irreversible; examples include peripheral neuropathies, myelopathy, neuropsychological disorders, neuro-ophthalmic conditions, and encephalopathy. Many of these disorders are linked to deficiencies in B vitamins, especially vitamin B₁. Therefore, management must be tailored to the patient’s specific circumstances.

This story was translated from Univadis France, part of the Medscape Professional Network.