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Gastric Bypass Vitamin Deficiencies

Gastric Bypass Vitamin Deficiencies

There are a few weight loss surgery options to choose from - gastric sleeve, gastric bypass, duodenal switch and the adjustable gastric band. Weight loss surgery, no matter the method, can be life-changing for the person receiving it.

Going through gastric bypass surgery is a large feat on its own. According to the American Society for Metabolic and Bariatric Surgery (ASMBS), gastric bypass surgery is a two-step process.

First, the stomach is made into a small pouch. This pouch can hold approximately 30 cubic centimeters ( 1 oz) in volume. Next, the small intestine is divided, and the bottom end of the small intestine is connected to the stomach pouch created. This results in a stomach pouch with tiny amounts of food and liquid and a reduced ability to absorb nutrients and calories via the small intestine.

Pros of gastric bypass surgery mentioned by ASMBS:

●    Significant long-term weight loss

●    Restriction placed on the amount of food consumed

●    50% or greater excess weight loss maintained

Cons of gastric bypass surgery mentioned by ASMBS:

●    Can result in long-term vitamin and mineral deficiencies

●    Is a more complex procedure that can result in complications

●    Requires adherence to a dietary and lifelong vitamin and mineral supplement regimen and going to follow up appointments

Besides continuing to follow your prescribed diet to lose weight at a healthy rate, you should also keep up with your supplement regimen. Vitamin deficiency after gastric bypass is a genuine possibility due to the nature of the procedure. Multiple vitamin deficiencies can occur due to the bypass of the small intestine and stomach. The bypass can cause problems because it alters the body’s ability to absorb certain nutrients.

In particular, seven vitamins and minerals require close monitoring post-gastric bypass to avoid deficiency:

  1. Calcium
  2. Copper
  3. Folate/Folic Acid
  4. Iron
  5. Vitamin B12
  6. Vitamin D
  7. Zinc
Vitamin deficiencies are always a concern for bariatric patients. 

Calcium and Vitamin D

Starting with calcium and vitamin D, a deficit in these two vitamins have been observed along with overactive parathyroid glands in patients with recent gastric bypass surgery.

The body tries hard to balance calcium, vitamin D, and parathyroid hormone levels. But, gastric bypass alters the levels of calcium, vitamin D, and parathyroid hormone. So, they all need to be closely watched.

According to the FDA, the recommended daily value for calcium is 1300 mg per day, and for vitamin D, it is 20 mcg per day. Good dietary sources of calcium can come from leafy green vegetables, nuts, fortified foods, and dairy. Typically, supplements are needed for bariatric patients because they have an increased need. This is due to having a reduced small intestine surface to absorb vitamins and minerals.

In order to avoid vitamin deficiencies, it is important to take vitamins to ensure proper health following bariatric surgery.


Moving onto copper, this nutrient acts as an antioxidant in the human body.

Meat, vegetables, legumes, and whole grains all contain copper. The recommended daily value for copper in adults is 0.9 mg per day.

Copper deficiency can occur alongside iron deficiency. Symptoms can be difficulty walking, heart enlargement, nerve damage, skin changes, and increased muscle tone or spasticity.

In general, a copper deficiency can lead to a variety of neurological and psychiatric disorders.

Paying attention to this mineral is crucial because copper absorption happens mainly in the small intestine, which is bypassed during gastric bypass surgery. Therefore, it is important to keep up the supplement routine prescribed by your doctor and dietitian.

Folate/Folic Acid and Zinc

Folic acid or folate is an important nutrient for the body because it helps make new cells, like neurons and red blood cells. Fortified cereals, legumes, fruits, leafy greens, and other vegetables contain this nutrient.

Folate deficiency can show up as anemia, as well as nervous system and psychiatric problems. For women trying to become or are currently pregnant, folate is vital to the fetus's healthy development. Deficiency in folate while pregnant can result in birth defects. As for zinc, any process that disrupts the intestinal wall, like gastric bypass surgery, can reduce zinc absorption and cause deficiency.


Iron is an essential nutrient for the body. Both vegetables and meat contain iron.

●    Non-heme iron in vegetables

●    Heme iron in meat

The body absorbs heme iron quickly in comparison to non-heme iron. According to the FDA, the daily value for iron is 18 mg per day for adults. Both the duodenum and the jejunum, which are parts of the small intestine, play a vital role in the absorption of iron in the body. Therefore, gastric bypass surgery will significantly affect iron absorption.

Iron deficiencies can be dangerous for bariatric patients. 

Iron deficiency shows up as anemia, general weakness, irritability, pica, fatigue, and brittle nails. Staying on your recommended iron supplementation regimen will help prevent any symptoms of vitamin deficiency after gastric bypass.

Vitamin B12

Vitamin B12 plays an important role in nervous system function and helps with the growth and replication of cells. It is commonly found in meat products and dairy. The current recommended daily value for vitamin B12 is 2.4 micrograms per day. Vitamin B12 deficiency is one of the most common among people who have had gastric bypass surgery.

The symptoms of vitamin B12 deficiency can show up as anemia, neuropathy, and cognitive difficulties.  The absorbing vitamin B12 involves both the duodenum, which is bypassed during gastric bypass surgery and the ileum. Therefore, if vitamin B12 deficiency is seen, an oral supplement or injection of the vitamin may be needed.


When considering the overall pros and cons of gastric bypass surgery, remember the risks and consequences involved. For example, complications can occur if aftercare instructions are not followed. One of these complications includes vitamin and mineral deficiencies.

Above all, it is important to follow the dietary and supplement advice from your dietitian and doctor. Doing so will help you avoid common nutrient deficiencies after gastric bypass. Some nutrients to keep in mind are copper, vitamin B12 and D, calcium, folic acid, and zinc. If you notice any symptoms related to vitamin deficiency, please consult with your doctor to figure out the next steps.

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Kaelyn Johnson, MPH, RD


Kaelyn Johnson is a Registered Dietitian who earned her Master of Public Health degree from Loma Linda University. She has worked in both a skilled nursing facility and an outpatient dialysis center.

Gintas Antanavicius, MD, FACS, FASMBS

Medical Reviewer

Dr. G is a co-founder of BariBuilder. A US-based expert surgeon with over 10 years of bariatric experience, he regularly publishes research in medical journals like SOARD, Obesity Surgery, etc.