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Avoiding Anemia and Nutritional Deficiencies Following Bariatric Surgery

September 30, 2009

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Despite its increasing popularity and considerable success, bariatric surgery does not come without important nutritional considerations. Many bariatric patients develop new or worsen preexisting iron and vitamin deficiencies, with some patients becoming anemic in the months and years following the procedure. This article discusses how nutritional deficiencies can develop and provides tips on how to avoid deficiencies and anemia following the procedure.

What if I have anemia or a nutritional deficiency before surgery?

It is not uncommon for morbidly obese patients to have anemia or nutritional deficiencies prior to surgery. In fact, some studies have indicated that up to 22% of bariatric surgery recipients had anemia prior to surgery.1 If you have anemia, it is important that your doctor or surgeon determine the cause of your anemia and to take steps to treat it before surgery. Detecting anemia and treating it are essential steps that can help reduce your need for a blood transfusion during or after surgery.2 Visit the Information Handout Anemia & Surgery for more information about anemia as it relates to general surgical procedures (not specific to bariatric surgery).

Nutritional deficiencies can also be common for morbidly obese patients considering bariatric surgery. According to Dr. John W. Baker, President of the American Society for Metabolic & Bariatric Surgery (ASMBS), about 60% of his patients have low levels of vitamin B12 prior to surgery and about 20% have iron deficiency. If your doctor or your surgeon detects that you have a nutritional deficiency, he or she will take appropriate steps to determine why this is occurring and recommend steps to return levels back to their normal range.

Candidates for Bariatric Surgery

Only morbidly obese patients are eligible to receive bariatric surgery, also known as weight loss surgery. People are considered morbidly obese if their body mass index (BMI) is greater than 40, or they have a BMI greater than 35 and are diagnosed with other chronic conditions. You can Calculate Your BMI by dividing your weight (kg) by your height (m2).

If you already decided to have the surgery, your surgeon should recommend that you take a multivitamin every day as part of preparing your body for the procedure. If you have a vitamin B12 deficiency or folate deficiency, taking this multivitamin may be all that your doctor recommends. If your doctor or surgeon detects that you have an iron deficiency, they may recommend that you take an oral iron supplement in addition to the daily multivitamin. You can read more about treatments for iron deficiency in our articles A Patient’s Guide to Oral Iron Supplements and Are Iron Injections Right for You? Be sure to tell your doctor or surgeon if you were not able to take all of the recommended oral iron doses and report any side effects you may be experiencing. All oral iron supplements will cause your stool to become dark in color.

How does the surgery alter my body?

There are many types of surgeries, known collectively as bariatric surgery, which can help morbidly obese patients lose weight when combined with healthy lifestyle behaviors and a nutritious diet. These surgical procedures help patients lose weight by altering the shape of the digestive tract and by effecting how the stomach and intestines process and absorb food.

Common Types of Bariatric Surgeries

Restrictive Only
Vertical banded gastroplasty (VBG)
Laparoscopic adjustable gastric band (LAGB)

Malabsorptive with Some Restriction
Biliopancreatic diversion (BPD)
Biliopancreatic diversion w/ duodenal switch (BPD-DS)

Restrictive with Some Malabsorption
Roux-en-Y gastric bypass (RYGB)
Vertical banded gastric bypass

How the surgical procedures alter the body can vary. Some procedures are “restrictive,” which means they reduce the capacity of the digestive tract and lower the number of calories a person can consume. Some procedures are “malabsorptive,” which means they alter the way the stomach and intestines absorb nutrients from food. Several bariatric procedures use a combination of the restrictive and malabsorptive approaches together.

The two types of surgeries that use restrictive methods only include vertical banded gastroplasty (VBG) and laparoscopic adjustable gastric banding (LAGB). Malabsorptive procedures with some restriction include biliopancreatic diversion (BPD) and biliopancreatic diversion with duodenal switch (BPD-DS). Restrictive procedures with some malabsorption include roux-en-Y gastric bypass (RYGB) and vertical banded gastric bypass. Discuss the different types of procedures with your surgeon to find out which one you have received or will receive.

Although the restrictive and malabsorptive approaches can help morbidly obese patients lose weight, altering the way you absorb nutrients can lead to iron deficiency, vitamin B12 deficiency or folate deficiency.1,3 Continued deficiencies of even one of these three nutrients can lead to a person becoming anemic over time. For the rest of their lives, patients who received bariatric surgery will need to take additional steps to prevent and possibly treat nutritional deficiencies and anemia.3

What can I do to prevent nutritional deficiencies?

There are several steps that you can take – both before and after surgery – to prevent nutritional deficiencies and reduce your risk for anemia. Some of these actions include:

Follow-up Programs – Once you have committed to receive the surgery, learning about the procedure and eating a healthy diet will begin when your surgeon enrolls you in a bariatric surgery program. Bariatric surgery programs start before surgery and continue well after surgery to help monitor your health and behavior. These programs can help you adjust to your new lifestyle and reinforce the importance of following dietary restrictions and taking the iron and vitamin supplements recommended by your surgeon. Participating in the follow-up portion of the programs is an essential part of staying healthy after bariatric surgery.

Eating Healthy – A healthy and balanced diet is important to reduce your chances of acquiring a nutritional deficiency. To avoid anemia, this includes eating foods that are rich in iron, vitamin B12 and folic acid. You can read about how your body uses these nutrients and why they are important for preventing anemia in our articles about Anemia and Nutrition: The Importance of Iron and The Importance of Essential Vitamins. Each of the articles list foods that contain these nutrients.

A Daily Mutlivitamin

Your doctor or surgeon should recommend a daily multivitamin that includes:

  • 100% of daily value for vitamin B12
  • 400 μg of folic acid
  • 18 mg of iron

An additional iron supplement may be recommended by your doctor or surgeon if you have an iron deficiency either before or after surgery.

Nutritional Supplementation – Taking nutritional supplements like multivitamins and oral iron can help ensure you receive enough nutrients through your diet. Because your stomach will be smaller, you may not be able to receive enough of the nutrients you need just from food. Concerning anemia-related nutrients, the multivitamin should include at least 100% of daily value for vitamin B12, 400 μg of folic acid, and 18 mg of iron.4 Even though the multivitamin contains iron, patients with a known iron deficiency may also need to take oral iron. You can read more about treating iron deficiency in our articles A Patient’s Guide to Oral Iron Supplements and Are Iron Injections Right for You?

Nutrient Absorption – In addition to getting enough nutrients in your diet, it can be important to increase your body’s ability to absorb the nutrients when they are in your digestive system. You can maximize iron absorption by eating foods that contain vitamin C, like citrus fruits, with your iron-rich foods and oral iron. Other items, like tea, cola, milk, coffee, calcium supplements and the hormone levothyroxine can decrease the amount of iron that is absorbed from food and supplements. Generally it is best to wait two hours before consuming these liquids or medications. For more tips on increasing iron absorption, read the article Anemia and Nutrition: The Importance of Iron.

What can my doctor do to monitor for deficiencies?

Regular check-ups with your surgeon and/or your primary doctor can help ensure that you are not developing nutritional deficiencies or anemia. These check-ups can either occur with your surgeon or with your primary care doctor, but it is important to discuss a follow-up schedule with both parties before surgery. Surgeons may enroll their patients in a bariatric surgery program that requires follow-up visits at the first, third, sixth and 12th months after the procedure. These scheduled visits help surgeons monitor your overall health and address any complications or symptoms you may be experiencing. Annual check-ups are recommended thereafter.

The visits at six and twelve months are especially important so that surgeons can perform simple blood tests to make sure patients are not acquiring nutritional deficiencies. Tests often measure the amount of vitamin B12, folate or iron that is stored in your body. If a nutritional deficiency is detected, your doctor will take appropriate steps to determine why this is occurring. It is possible that you may not have enough stored nutrients because your digestive tract is still not absorbing them properly from the food you eat and the supplements you’ve been taking. If this is the case, there are intravenous methods (through an IV) that directly inject nutrients into your bloodstream. Read more about other causes for Vitamin Deficiency Anemia, Iron Deficiency Anemia and other causes of anemia in the Information Handouts.

In addition to testing, it is important to tell your doctor and surgeon about any unusual symptoms you may be experiencing. Symptoms which may be caused by anemia include feeling tired, fatigued, weak, dizzy, irritable or short of breath. You may also have pale skin, brittle nails, chest pain, an irregular heartbeat, or coldness in your hands or feet. Anemia caused by a vitamin B12 deficiency can also cause your tongue to be smooth and bright red, and may lead to a tingling or numbness in your hands and feet. Without treatment, these symptoms may develop slowly and become more severe over time.

Hands and pillboxYour Health After Surgery

When combined with a healthy diet and lifestyle behaviors, bariatric surgery is an extremely helpful procedure that can assist morbidly obese patients shed excess weight and reduce the occurrence of obesity-related health conditions like hypertension, heart disease, diabetes, sleep apnea and high cholesterol.5

However, due to the considerable changes to the digestive tract, patients who receive bariatric surgery can develop new or worsen preexisting nutritional deficiencies, with some patients becoming anemic in the months and years following the procedure. To avoid these complications it is essential to eat a healthy diet, take your prescribed supplements and regularly visit your doctor to monitor your overall health and nutrient levels. Close communication with your doctor and surgeon will help them provide any necessary treatment for anemia or nutritional deficiencies.

See the link to the Centers for Disease and Prevention (CDC) Adult BMI Calculator as a convenience to readers. The links we offer are not endorsements or recommendations of other organizations, or their products or services. Visit our full Terms of Use and Privacy Policy for more information. It is recommended to consult your doctor about your individual BMI score.


  1. von Drygalski A, Andris DA. Anemia after bariatric surgery: more than just iron deficiency. Nutr Clin Pract. 2009 Apr-May;24(2):217-26. Link.
  2. Faris PM, Spence RK, Larholt KM, Sampson AR, Frei D. The predictive power of baseline hemoglobin for transfusion risk in surgery patients. Orthopedics. 1999 Jan;22(1 Suppl):s135-40. Link.
  3. American Society for Metabolic & Bariatric Surgery. Guidelines. Bariatric Surgery: Postoperative Concerns. Link. Revised: February 7, 2008.
  4. Allied Health Sciences Section Ad Hoc Nutrition Committee, Aills L, Blankenship J, Buffington C, Furtado M, Parrott J. ASMBS Allied Health Nutritional Guidelines for the Surgical Weight Loss Patient. Surg Obes Relat Dis. 2008 Sep-Oct;4(5 Suppl):S73-108. Link. (PDF)
  5. American Society for Metabolic & Bariatric Surgery. Metabolic & Bariatric Surgery Fact Sheet. Link. Revised: July 2009. (PDF)