Iron Deficiency After Bariatric Surgery

There is no question that the United States and other developed nations are experiencing an obesity epidemic: based on figures from 2003-2004, 32.3% of Americans are obese, with another 4.8% considered morbidly obese [1]. Both the popular media and the medical community have acknowledged this growing problem, and there has been an increasing focus on addressing obesity through diet, exercise, and medical treatments. But for those who are morbidly obese, these methods often do not produce satisfactory results. Such patients frequently turn to bariatric surgeries such as gastric bypass, laparoscopic adjustable gastric banding (LAGB), vertical banded gastroplasty (VGB), biliopancreatic diversion (BPD), and biliopancreatic diversion and duodenal switch (BPD-DS). With proven effectiveness in treating obesity and obesity-related comorbidities and an overall mortality rate of less than 1%, bariatric surgery is becoming increasingly popular [2].

However, despite its many positive effects in treating obesity, bariatric surgery is not without risk. Short-term complications associated with the procedures include anastomotic leak, pulmonary embolism, infection, and incisional hernia. Long-term complications are often related to metabolic abnormalities and nutritional deficiencies, such as a shortage of iron, vitamin B12, folate, calcium, and vitamin D. Since iron deficiency and the resulting anemia can significantly affect quality of life—especially with the majority of bariatric surgery patients being menstruating women—it is important to take a closer look at the relationship between iron deficiency and bariatric surgery and the importance of vitamin and protein supplementation.

Gastric bypass surgery, a malabsorptive procedure that affects nutrient absorption by bypassing a portion of the intestine, is particularly likely to lead to iron deficiency and related anemia. In fact, studies have reported up to a 50% rate of iron deficiency in the months and years following gastric bypass. There are several reasons why this procedure is prone to lead to iron deficiency:

Reduced Meat Consumption

People living in Europe and North America acquire about 2/3 of their body’s iron stores from heme iron, the type of iron found in meat. Studies have found that as many as 50% of gastric bypass patients develop an intolerance for meat that often results in vomiting, and 90% consume significantly less dietary iron up to 6-9 years after the operation [3,4]. However, lack of dietary iron can’t be the only explanation. Patients who have undergone a banding procedure typically have even less tolerance for meat. Paradoxically, a randomized trial comparing banding and bypass patients found iron deficiencies only in the bypass group.

Reduced Gastric Acid

Molecular iron is initially metabolized in the stomach, where gastric acid aids in converting it into its absorbable form, ferrous iron. Surgeries like gastric bypass reduce the number of cells that produce gastric acid, thereby significantly diminishing the amount of gastric acid that is secreted and available to metabolize iron [5]. Banding procedures, however, maintain the continuity of the digestive tract and tend to have lower rates of iron deficiency.
Loss of the Duodenum

As part of the gastric bypass procedure, the part of the small intestine known as the duodenum is excluded from the digestive system. As the duodenum is the place where heme iron is absorbed, the loss of this part of the intestine negatively impacts one’s ability to absorb heme. Therefore, it is not surprising that serum iron and hemoglobin concentrations tend to be significantly lower among bypass patients than among banding patients, whose duodenum is retained as part of the digestive system [6]. The gastric bypass procedure known as BPD-DS, however, preserves some of the duodenum’s functionality and may protect against iron deficiency.


Gastric bypass patients may experience gastrointestinal blood loss due to the loops of bowel that are excluded from the digestive tract during the procedure. This loop of bowel is also prone to an overgrowth of intestinal bacteria, which can cause intestinal cells and their iron stores to be damaged and excreted. In other instances, marginal ulcers may occur and result in increased blood loss.

Weight Loss

It has been hypothesized that the rapid weight loss associated with bariatric surgery may contribute to iron deficiency in patients, but evidence suggests that the amount of weight lost and the speed with which it is lost has minimal or no influence on the degree of iron deficiency [4].

While gastric bypass procedures are more often associated with iron deficiency than purely restrictive bariatric procedures (those that maintain the digestive system’s continuity but limit food intake), certain groups of people are always at a higher risk for iron deficiency:

  • Women of Childbearing Age
    Menstruating women are more prone to developing an iron deficiency than men or non-menstruating women, regardless of whether they undergo a bypass or banding bariatric procedure. This may be due to lower preoperative stores of iron, the resumption of menstruation postoperatively, or a combination of the two. Whatever the reason, menstruating women are at a higher risk for iron deficiency and its resulting complications, including hospitalization and transfusions.
  • Pregnant Women
    Bariatric surgery is known to improve female fertility, and many women intend to have children sometime after their surgery. However, since iron requirements increase during pregnancy, this can contribute to an even greater rate of iron deficiency. Because anemia is damaging to the mother’s health and may result in premature birth or low birth weight, banding procedures may be a better option than gastric bypass for women planning a future pregnancy.
  • Children and Adolescents
    Bariatric surgery is being performed successfully on adolescents, with low mortality rates and resulting in an improved quality of life. However, this group of patients may be at an increased risk for iron deficiency after surgery. One reason is that obese children and adolescents—particularly females—have been found to have lower iron levels than their peers of a normal weight, meaning they may be at risk for iron deficiency even before undergoing a bariatric procedure. Additionally, patients who receive a bariatric procedure at a young age may face long-term nutritional deficiencies. This is particularly worrisome among girls, who already may be predisposed to iron deficiency.

Treatment of Iron Deficiency

Nutritional deficiencies are a recognized complication of bariatric surgery, and the majority of surgeons regularly prescribe a multivitamin to all patients. However, one study found that 24 of 79 patients still developed an iron deficiency after surgery even while taking a multivitamin, suggesting that additional supplements may be necessary to prevent anemia. This is particularly true among menstruating women, and many surgeons now prescribe both iron supplements and a multivitamin to these patients.

Taking vitamin C in addition to an oral iron supplement has been shown to raise hemoglobin levels more than iron alone. By increasing the acidity of the gastrointestinal tract, vitamin C helps reduce iron to its more absorbable ferrous form. This may enhance the absorption of iron and aid in the prevention and treatment of iron deficiency after bariatric surgery.

About the Author

Matt Glosson, PhD, is a medical biologist at Washington University School of Medicine in St. Louis, MO. Matt conducts specialized research in the area of cardiovascular disease, and has developed a particular interest in the related field of obesity treatment. As someone who feels a deep compassion for people struggling with obesity and its related health complications, Matt strives to make science’s latest findings accessible to all. He designed his weight loss website with this goal in mind, offering information and support to all who need it.

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