Health Encyclopedia

Risks of Bariatric Surgery: Anemia

What is anemia after bariatric surgery?

Anemia is a common side effect of weight-loss surgery. It's a condition in which your blood contains lower than normal levels of red blood cells or red blood cells that contain too little of the protein hemoglobin. This is a problem because hemoglobin is the substance that carries oxygen throughout the body.

What are the causes of anemia after bariatric surgery?

Vitamin and mineral deficiencies are common in people after surgery. Weight-loss surgery, also known as bariatric surgery, limits how much food you are able to eat. It also changes the way your body absorbs essential vitamins and minerals from food. After weight-loss surgery, you'll need to take daily vitamin and mineral supplements to help prevent these problems.

More specifically, anemia can result from too little iron intake or not enough iron absorption after bariatric surgery. Not getting enough folic acid and vitamin B12 can also cause anemia. Your body needs all these nutrients to make hemoglobin and healthy red blood cells.

After bariatric surgery, especially a Roux-en-Y gastric bypass (RYGB), you may also not be able to eat red meat because your body may have difficulty digesting it. This can make you more likely to have anemia, because red meat is a major source of iron in the diet.

Weight-loss surgery can reduce the level of stomach acids that break down foods. This can also lead to nutrition-related anemia. In some types of bariatric surgery, including the RYGB procedure, the intestines are rerouted to bypass the duodenum and jejunum. These are the parts of the small intestine where most of the ingested iron and calcium are absorbed. This makes it harder for your body to absorb iron and other nutrients.

Who is at risk for anemia after bariatric surgery?

Teens, women who still have their periods, and pregnant women are at higher risk of developing anemia after bariatric surgery.

Many people may be anemic even before they have bariatric surgery because anemia is common in people who are severely obese. Chronic inflammation caused by obesity may lead to anemia by affecting the immune system. In these cases, the surgery alone may not have caused the anemia.

What are the symptoms of anemia?

Because anemia results in low levels of oxygen in your blood, your heart has to work harder in order to circulate more blood. The condition can cause a number of symptoms:

  • Fatigue
  • Difficulty exercising
  • Chest pains (especially if you have heart disease)
  • Cold feet and hands
  • Feeling short of breath
  • Headaches
  • Dizziness
  • Unusually pale skin

How is anemia diagnosed?

Your doctor may want to check your stool for blood and do a complete blood count to measure your hemoglobin. If blood is present in your stool, he or she may suggest a colonoscopy and upper gastrointestinal radiologic study or endoscopy.

How is anemia treated?

People with severe anemia may need a blood transfusion to replenish oxygen-rich red blood cells. At the recommendation of your health care provider, you will also be followed by a nutritionist or registered dietitian to make sure you diet has the proper amount of iron-rich foods and vitamins and minerals. Your health care provider will also monitor your blood periodically.

Can anemia be prevented after bariatric surgery?

After bariatric surgery, your doctor will need to watch you for anemia for the rest of your life because the condition may not develop until many years later. This includes getting regular blood tests to check for nutritional deficiencies, including anemia. Guidelines recommend having your serum iron measured 6 months after weight-loss surgery and at least once a year after that, along with a complete blood count

Your doctor will most likely have you work with a nutritionist or registered dietitian to watch your diet after surgery. It's important to take all the recommended daily vitamin and mineral supplements after bariatric surgery to prevent anemia and other nutritional deficiencies. It's also important to eat iron-rich foods such as:

  • Lentils, peas, and beans
  • Dried prunes, apricots, raisins, and other fruits
  • Cereals and breads that are fortified with iron
  • Dark, leafy green vegetables like spinach
  • Tofu
  • Prune juice
  • Meat, especially red meat, if possible

Vitamin C from foods and from supplements can help your body absorb iron, so be sure to add foods rich in vitamin C, like citrus fruits, to your diet, as well.

If you had the RYGB procedure, the amount of iron in a standard multivitamin — about 18 mg — may not be enough to prevent anemia. Your doctor may give you more iron to take.

If you are a teen boy or girl, or a menstruating woman, you may need extra iron, no matter what type of weight-loss surgery you had. Your health care provider will use blood tests to help figure out your iron supplement dose. This is important because too much iron can be as bad for you as too little iron.

Frequent follow-up visits with your doctor can help prevent anemia and its long-term complications. Iron deficiency anemia can also occur from chronic bleeding in the intestine, usually the large intestine, from many sources, such as polyps and cancers.

Key points

Anemia is a common side effect of weight-loss surgery. This is a problem because hemoglobin is the substance that carries oxygen throughout the body.

  • Bariatric surgery changes the way your body absorbs essential vitamins and minerals from food.
  • Anemia can result from too little iron intake or not enough iron absorption and not getting enough folic acid and vitamin B12 can also cause anemia.
  • Teens, women who still have their periods, and pregnant women are at higher risk of developing anemia after bariatric surgery.
  • Because anemia results in low levels of oxygen in your blood, your heart has to work harder in order to circulate more blood causing symptoms:
    • Feeling short of breath
    • Headaches
    • Dizziness
    • Unusually pale skin
    • Fatigue
  • Guidelines recommend having your serum iron measured 6 months after weight-loss surgery and at least once a year after that, along with a complete blood count.
  • Your doctor will most likely have you work with a nutritionist or registered dietitian to make sure you are getting the proper amount of vitamins and minerals and iron-rich foods.
  • Frequent follow-up visits with your doctor can help prevent anemia and its long-term complications. 

Next steps

Tips to help you get the most from a visit to your health care provider:

  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.


Medical Reviewers:

  • Fincannon, Joy, RN, MN
  • newMentor board-certified, academically affiliated clinician