Implications of Bariatric Surgery on Absorption of Nutrients and Medications

Mary Carpenter, PharmD; Mary Ellen Pisano, PharmD; Christopher M. Bland, PharmD, BCPS, FIDSA


US Pharmacist. 2016;41(12):HS-2-HS-8. 

In This Article

Nutritional Deficiency and Supplementation

Morbid obesity (BMI ≥40) has been shown to be associated with micronutrient deficiency, although the mechanism is not completely understood. Potential mechanisms may include impaired expression of transporter proteins due to chronic inflammation, small intestinal overgrowth syndrome, and eating behaviors favoring high energy-dense foods with poor micronutrient content.[17] With the high prevalence of preexisting deficiencies in the obese population, the importance of monitoring for deficiencies and providing adequate supplementation, as well as assessing adherence to supplementation post surgery, is vital. Data analyzing adherence to supplementation are scarce; however, adherence seems to be low according to the available literature. Brolin and Leung followed patients over a 10-year period postoperatively and reported that only 33% of patients complied with multivitamin supplementation.[18] Sawhney et al assessed adherence in adolescents 6 months post surgery and found that 30.7% of patients remained adherent to multivitamin regimens.[19]

In addition to supplement adherence, the type of procedure performed and the nutrient salt administered also impact whether or not a deficiency is likely to occur. Malabsorptive procedures can lead to nutrient deficiency through changes in biliary and pancreatic functions, alterations in GI transit time/gastric acid secretion, bypass of the duodenum (a primary site of absorption), and promotion of small intestinal bacterial overgrowth (SIBO). Restrictive procedures can also lead to nutrient deficiency via food intolerance caused by nausea, vomiting, and regurgitation. Deficiencies of fat-soluble nutrients or nutrients absorbed in the bypassed section of the GI tract are most common and include folate, iron, calcium, and vitamins B1, B12, A, and D. A summary of these deficiencies and their associated prevalence rates can be found in Table 2.[9,17]

In general, all patients post bariatric surgery should take a multivitamin supplement indefinitely, with the percentage of recommended daily dose dependent on the type of surgery. LAGB/LSG patients should take a multivitamin with 100% of the recommended daily dose of nutrients, and RYGB patients should take a multivitamin with 200% of the recommended daily dose of nutrients.[17] Patients should also receive daily calcium supplementation in addition to the multivitamin.

Reduced gastric pH following gastric bypass affects calcium absorption.[17] Patients should use calcium citrate rather than calcium carbonate, as the citrate form does not require acid to be absorbed. Although calcium citrate is more expensive and contains less calcium per tablet, it is associated with less GI upset and does not need to be taken with food. It is difficult to assess true calcium deficiency due to homeostatic mechanisms of calcium in the blood via renal calcium reabsorption and bone resorption. Thus, it is important to ensure that patients' vitamin D, 25-hydroxy levels remain within normal range and to provide adequate amounts of vitamin D to maintain normal levels for proper calcium absorption from the GI tract. Most calcium citrate formulations contain vitamin D, making cosupplementation more convenient.

This patient population is also at increased risk of anemia secondary to potential deficiencies in iron, folate, and vitamin B12.[20] The primary site for iron absorption is the duodenum, which is bypassed in RYGB procedures. The reduced gastric acid environment of the stomach can lead to decreased conversion of iron from the ferric form (Fe3+) to the ferrous form (Fe2+), which is required for absorption. In patients identified as having iron deficiency anemia (microcytic anemia) following gastric bypass surgery, coadministration of vitamin C with iron supplementation can increase the conversion of iron to its absorbable form by reducing the pH of the stomach.[21] Vitamin B12 and/or folate deficiencies post surgery can lead to development of megaloblastic (macrocytic) anemia. Factors underlying vitamin B12 deficiency are likely due to reduced intake of meat, diminished contact of food with gastric acid, and decreased secretion of intrinsic factor. The limited number of parietal cells in the stomach post surgery leads to subsequent decrease in cobalamin–intrinsic factor complex formation and absorption. On the other hand, folate deficiency is likely due to bypass of the proximal small intestine, which is the primary site of absorption. Folate supplementation is important, especially for women who become pregnant after bariatric surgery, because maternal folate deficiency can lead to neural tube defects in newborns.[9,22]

Deficiencies in lipid-soluble vitamins (A, D, E, K) may occur post surgery due to fat malabsorption resulting from biliopancreatic diversion. Although deficiency of vitamin D is more common as previously discussed, deficiency in vitamins A, E, and K is uncommon if patients are adherent to multivitamin regimens. However, these vitamins still play an important role in maintaining good health. Vitamin K is required for development of certain clotting factors (II, VII, IX, X) and for chondrogenesis, a process important for fetal development. Vitamin E functions as an antioxidant and protects cells, tissues, and organs from damaging effects caused by free radicals. Vitamin A is important for vision; however, supplementation should be cautioned in women of childbearing age because of teratogenic effects with toxic concentrations. Pre- and postoperative monitoring for deficiency in these vitamins is recommended.[22]

In addition to malnutrition, deficiencies can lead to development of other disease states and comorbid conditions. Patients can develop low bone density or osteoporosis (from calcium/vitamin D deficiency), muscle contractions, pain/spasms (from calcium/magnesium deficiency), beriberi, neuropsychiatric complications (from vitamin B1 deficiency), and anemia (from iron, folic acid, vitamin B12 deficiency), as well as countless other conditions. Thus, it is important to educate bariatric patients on the importance of adherence to supplementation both pre- and postoperatively.[17]

Among the benefits of bariatric surgery is that many patients have significant attenuation or resolution of GERD symptoms post surgery. If a patient had been on chronic acid-suppressing therapy prior to surgery, he or she may no longer need to continue this therapy post surgery. The impact of acid-suppressing medications, particularly proton pump inhibitors, on absorption of nutrients has been well documented. Therefore, an attempt to remove acid-suppressing therapies should be performed post surgery with the goal to limit absorption issues of several nutrients including calcium, iron, and vitamin B12, which may limit complications associated with these deficiencies.[23,24]