Macro and micronutrient needs of bariatric surgery patients: a review

Featured article in the Winter 2016 Nutrition Close-Up; written by Meagan Moyer, MPH, RDN, LD

Bariatric surgical procedures for the treatment of morbid obesity are becoming increasingly prevalent since their inception in the 1970s. According to a survey by the International Federation for the Surgery of Obesity and Metabolic Diseases (IFSO), 468,609 bariatric procedures were performed in 2013, up 37% from 2011. In 2013, more cases were performed in the United States and Canada (154,276) than any other region of the world. The IFSO predicts that the number of bariatric surgical procedures will continue to rise.1

The most common bariatric surgical procedure performed in 2013 was the Roux-en-Y gastric bypass (RYGB) at 45% of all cases. This was followed by the sleeve gastrectomy (SG) procedure at 37% and the adjustable gastric band (AGB) at 10% of all cases worldwide. Given the rise in popularity of bariatric surgery, it is likely health professionals will encounter these individuals as a patient or client. This article serves as a review of the most common nutritional concerns in individuals who have had RYGB or SG.


Macro and micronutrient needs

All bariatric surgeries restrict the amount of food a person can eat at one time, which helps promote weight loss. RYGB and SG also affect the secretion of gut hormones that lead to decreased hunger and increased satiety. The gastric manipulation involved with RYGB and SG also result in micronutrient malabsorption.2  Therefore, the restrictive and malabsorptive nature of RYGB and SG procedures place patients at a relatively high risk for nutritional deficiencies, both immediately post-op and long-term.



Protein malnutrition is not commonly seen in RYGB and SG patients unless oral intake is poor. The goal for protein recommendations after surgery is to preserve lean body mass and minimize muscle loss. Exact protein recommendations have not been defined, but most bariatric physicians and dietitians agree on a protein goal of 60-80 grams per day or 1-1.5 grams per kilogram of ideal body weight per day.3


It is not necessary for bariatric surgery patients to consume more protein than the recommended amounts. Due to decreased stomach volume, consuming too much protein will likely limit their intake of needed carbohydrates, fat, and micronutrients. Nutrition counseling should therefore encourage a balanced diet of all macronutrients once protein needs are met.3


Vitamin B-12

Bariatric surgery patients absorb less vitamin B-12 from dietary protein due to a reduction in gastric acids needed to cleave the vitamin from the protein source. Vitamin B-12 needs are especially increased in RYGB patients because the section of the duodenum where B-12 attaches to intrinsic factor (IF) for absorption is bypassed. Vitamin B-12 should be supplemented with 350 micrograms sublingually once a day, 500 micrograms intranasally once a week or 1000 micrograms intramuscularly once a month.2

Vitamin B-12 is stored in the body for up to two years and deficiencies are often not seen until long after bariatric surgery. Therefore, patients who do not adhere to supplementation recommendations and/or are not routinely monitored by healthcare professionals are at the greatest risk for vitamin B-12 deficiency.2


Calcium and Vitamin D3

Calcium and vitamin D requirements are slightly higher for RYGB and SG patients than the general population due to decreased dietary absorption. After bariatric surgery, the calcium requirement for men and premenopausal women is 1,200 mg per day and 1,500 mg per day for postmenopausal women. Calcium citrate is the preferred form of supplemental calcium because it does not require a highly acidic environment for absorption.2


Vitamin D3 should be taken with calcium to aid in absorption of both micronutrients. Studies have shown an intake of less than 2,000 IU of vitamin D3 per day may lead to deficiency.  It is recommended RYGB and SG patients take 3,000 IU per day of vitamin D3. This can be achieved through multivitamin/mineral and calcium with vitamin D3 supplementation.2



As with calcium, iron needs are higher after RYGB and SG due to decreased stomach acid needed for absorption. After RYGB, the major sites of iron absorption (duodenum and proximal jejunum) are bypassed. If patients are taking two multivitamins per day with at least 18 mg of iron in each tablet (36 mg per day total), iron supplementation is likely sufficient. However, pre-menopausal women may require an additional 50 to 100 mg of elemental iron per day. It is important for patients to separate intake of iron-containing supplements and calcium supplements by at least two hours for maximum absorption.2



The nutrition needs of individuals who have bariatric surgery are unique. Short-term and long-term monitoring of nutrition-related labs is essential to preventing deficiencies. The restrictive and malabsorptive nature of RYGB and SG require life-long micronutrient supplementation for optimal health and weight loss outcomes.



Meagan Moyer, MPH, RDN, LD is the Coordinator of Nutrition Services at Emory Bariatric Center based  at Emory University Hospital in Atlanta, Georgia.



  1. Angrisani L, Santonicola A, Iovino P, et al. Bariatric Surgery Worldwide 2013. Obes Surg. 2015;25:1822-1832.
  2. Mechanick JI, Kushner RF, Sugerman HJ, et al. AACE/TOS/ASMBS guidelines: American Association of Clincal Endocrinologists, the Obesity Society, and American Society for Metabolic and Bariatric Surgery medical guidelines for clinical practice for the perioperative nutritional, metabolic and non-surgical support of the bariatric surgery patient. Endrocr Pract. 2008;14(Suppl. 1):S1-S70.
  3. Academy of Nutrition and Dietetics Evidence Analysis Library. Bariatric Surgery Nutrition Care. Internet: Accessed October 23, 2015.



Key Messages:

  • Rates of bariatric surgery procedures for the treatment of morbid obesity are rising in the United States and worldwide.
  • Protein plays a crucial role in healing and in the preservation of lean body mass after bariatric surgery.
  • Due to alterations of the gastrointestinal tract in bariatric surgery, patients will require lifelong micronutrient monitoring and supplementation.
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