Vitamin B12 After Metabolic and Bariatric Surgery

Vitamin B12 After Metabolic and Bariatric Surgery - Bariatric Fusion

You probably know that metabolic and bariatric surgery (MBS) can support weight loss goals and positively affect the outcome of many obesity-related conditions.

You might not know that after surgery, your body has a harder time absorbing many essential nutrients, putting you at risk for certain vitamin deficiencies. That’s why abnormal vitamin and mineral levels are much higher in the bariatric population.

Fortunately, the American Society for Metabolic and Bariatric Surgery (ASMBS) has designed research-based nutritional guidelines to support optimal bariatric health, including the recommendation of lifelong bariatric supplements.*

In this article, we’ll explain why vitamin B12 (cobalamin) is a common bariatric vitamin deficiency and why it can have lasting effects on your body if not treated. We’ll list common symptoms of vitamin B12 deficiency and recommend the best bariatric vitamin supplements to consider.*

The Role of Vitamin B12

Your body needs vitamin B12 for the proper function of the nervous system, healthy red blood cells, and making DNA, so it’s critical that you get enough. (1)

You can get this water-soluble vitamin from animal products like fish, meat, eggs, dairy, fortified foods, or as a dietary supplement.

The vitamin B12 absorption process starts in your mouth but mainly occurs in your stomach and small intestine with the help of intrinsic factor, a protein that helps your body assimilate.

Why There’s a Higher Risk of Vitamin B12 Deficiency After MBS

The risk of micronutrient deficiencies varies based on the type of metabolic and bariatric procedure undergone. Common deficiencies include vitamin B1, folic acid, vitamin D, iron, copper, and of course, vitamin B12. (2) To support optimal health, it is often suggested that you take bariatric supplements for life.*

There are a few reasons why there’s such a risk for vitamin B12 deficiency. First, your body needs to absorb and use vitamin B12, but malabsorption and the lack of intrinsic factor can result in less-than-optimal amounts of vitamin B12. (3)

You also eat smaller portions after MBS and may have difficulty eating enough whole foods to get your daily fill.

Patients who have undergone MBS are more likely to experience long-term nutritional deficiencies when compared to the general population. These long-term issues include a higher occurrence of iron deficiency for men and a higher occurrence of vitamin B12 deficiency for women. (4)

Symptoms of Vitamin B12 Deficiency

There are a few things to look for that indicate a vitamin B12 deficiency. The list includes (but is not limited to) the following symptoms:

  • Anemia
  • Constipation
  • Fatigue
  • Headaches
  • Mouth lesions
  • Irritability
  • Neurological issues

What are the ASMBS Guidelines for Supplementing?*

The ASMBS recommends that metabolic and bariatric surgery patients get 350 mcg - 1000 mcg of vitamin B12 daily from food and supplements. Of course, this number can differ depending on your individual needs.*

Generally, it’s suggested that MBS patients take higher supplemental doses of vitamin B12 to compensate for the loss of stomach acid and intrinsic factor following a gastric procedure, such as roux-en-y gastric bypass (RYGB) or gastric sleeve.*

It’s often recommended that you take a bariatric-specific multivitamin for life. In some cases, you may need to take a separate vitamin B12 supplement in addition to your bariatric multivitamin to support additional health needs.*

Vitamin B12 Supplement Forms (and Why They Matter)*

There are multiple forms of vitamin B12 supplements on the market, including methylcobalamin and cyanocobalamin.

The liver converts cyanocobalamin into methylcobalamin – the more biologically active form of vitamin B12. Currently, one form isn’t recommended over another for metabolic and bariatric surgery patients, though it should be noted that methylcobalamin doesn’t require further conversion by the body to be absorbed.

There are different ways to receive vitamin B12 supplementation, from nasal sprays and B12 injections to sublingual or quick-dissolving tablets. (5) Based on the route of administration, vitamin B12 can be absorbed directly into the bloodstream, through the small intestine, or a small percentage can be passively absorbed without intrinsic factor.*

Only take dietary supplements as recommended by your healthcare team.*


Vitamin and mineral deficiencies are notably higher in patients after metabolic and bariatric surgery. All nutrients are essential for daily body functions and wellness.

Dietary sources of nutrients are always recommended before supplementation, except in metabolic and bariatric surgery, when it’s harder for your body to absorb nutrients from food properly.*

The formulation of most bariatric-specific multivitamins includes vitamin B12 levels that support optimal health. But before you take any supplements, consider working with a dietitian for a personalized long-term nutritional plan.*



  1. National Institutes of Health (NIH). 2022
  2. Annu Rev Nutr. 2013; 33:183-203 [PMID: 23642197]
  3. Obes Surg. 1995; 5(2):154-158 [PMID: 10733805]
  4. Int J Environ Res Public Health. 2021; 18(9):4541 [PMID: 33922904]
  5. SOARD. 2020; 16(2):175-247 []

*These statements have not been evaluated by the Food & Drug Administration (FDA). These products are not intended to diagnose, treat, cure or prevent any disease.

This blog is for information and education purposes only. This information is not intended to substitute professional medical advice, diagnosis, or treatment. Please consult with your bariatric surgeon or another qualified healthcare provider with any questions in regards to a medical condition. A qualified healthcare professional can best assist you in deciding whether a dietary supplement is suitable based on your individual needs.

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