bariatric surgery

An Overview of Nutrition for Bariatric Surgery

Regina Kosiba, RD, LD
Bariatric Dietitian, Del Sol Bariatric Center, El Paso, Texas

Kosiba R. An overview of nutrition for bariatric surgery [published online October 23, 2019]. Nutrition411.


As the rates of obesity continue to rise across the US population, the public is turning more toward bariatric surgery, specifically Roux-en-Y gastric bypass and vertical sleeve gastrectomy, compared with conventional weight loss methods of diet and exercise. Nutrition professionals must be well-versed in evidence-based recommendations for this route of surgical weight loss in order to prevent postoperative complications and nutrient deficiencies.

According to the National Institutes of Health, the set eligibility criteria to undergo bariatric surgical procedure includes having a body mass index (BMI) of at least 40 kg/m2 without coexisting medical problems or a BMI of at least 35 to 40 kg/m2 with at least 1 severe obesity related comorbidity, including type 2 diabetes, hypertension, hyperlipidemia, and obstructive sleep apnea.1 Prior to undergoing a bariatric procedure, patients meeting these criteria must first be educated on what part they play in achieving postoperative success. Registered dietitian nutritionists (RDNs) hold a vital role in this education, as lifestyle change starts preoperatively in order to better maintain postoperative treatment adherence.

Preoperative bariatric nutrition guidelines are similar to those described in traditional weight loss education. Examples include decreasing portion sizes by eating with a portion plate at meals, as well as choosing healthy options from each food group. RDNs should encourage daily hydration of at least 64 oz of non-carbonated, non-caffeinated, and non-caloric beverages. Physical immobility often presents as an obstacle for patients who are overweight. Therefore, recommending at least 30 minutes of “mindful movement” per day can be advantageous for patients in learning to form healthy habits.

Postoperatively, nutrition education becomes more complicated and includes stages of food texture progression, beginning with clear liquids from day 1 to day 2 post-procedure and advancing to regular textures 6 to 8 weeks post-procedure (Table 1).2 Patients are instructed to begin with clear liquids at room temperature for 24 to 48 hours after surgery, increasing the volume gradually to reach 8 cups or more per day (2 L). In addition, patients should drink liquids in small portions as tolerated, with 1 serving including no more than half of a cup. To prevent gastrointestinal upset, it is also recommended to separate liquids from solids by avoiding drinking beverages 15 minutes before or 30 minutes after eating.

Table 1: Current Texture Advancement in Clinical Practice for Noncomplicated Patients2

Diet Phase

Duration (days)

Clear liquid


Full liquid




Mechanically altered soft




Due to rapid weight loss following surgery, muscle wasting is common. It is therefore recommended to measure muscle mass at each follow-up visit to ensure decreases in muscle mass are minimal compared with overall fat loss. Studies have correlated the consumption of protein intake with maintenance of muscle mass during postoperative weight loss.3 The American Society for Metabolic and Bariatric Surgery (ASMBS) guidelines instruct healthcare providers to coach patients to consume a high protein intake of 60 to 80 g per day or 1 to 1.5 g/kg ideal body weight per day.4

Postoperative Vitamin/Mineral Supplementation for the Bariatric Patient


Nutrition-related laboratory values are closely monitored by the bariatric physician and dietitian every month in the first postoperative year, every six months in the second year, and annually thereafter.5 Reasons for depleted nutrition-related laboratory values can be attributed to a number of factors. Among these factors are a drastic decline of micro- and macro-nutrients from postoperative intake due to their decreased stomach size. In addition, a restructured gastrointestinal tract may cause malabsorption of vital micronutrients. Emesis and diarrhea caused by postsurgical gastrointestinal upset is also a common cause of micronutrient losses.


Lifelong adherence to micronutrient supplementation is vitally important, as bariatric surgery recipients are at great risk of developing nutrient deficiencies causing osteoporosis, anemia, or hair loss. ASMBS outlines evidenced-based recommendations for vitamin/mineral supplementation guidelines that are to be strictly followed postoperatively (Table 2).4,6


Table 2: AMBS Vitamin/Mineral Guidelines for Noncomplicated Postoperative Bariatric Patients


2 adult multivitamin-mineral supplements/day (200% of the RDA), containing iron, folic acid, zinc, copper, selenium, and thiamin.

Calcium Citrate:

1200–1500 mg/day. Single doses should not exceed 600 mg and must be separated by ≥2 hours from

iron supplements or a multivitamin that contains iron.

Vitamin D3 (cholecalciferol):

3000 IU/day. If depleted, titrations to reach normal concentrations of 30 ng/mL


45–60 mg elemental Iron/day; may be included in multivitamin or taken as separate supplement. Women of childbearing age are at increased risk of anemia and should consume 50–100 mg elemental Fe/day. 5


250–350 μg/day or 1000 μg/week sublingual

As noted above, nutrition-related laboratory values are closely monitored by the bariatric team. If nutrition-related depletion is evident, the healthcare professional should first investigate a patient’s compliance to their vitamin schedule. Nonadherence can often arise due to financial issues, forgetfulness, and/or taste aversions.

The bariatric dietitian is responsible for working closely with the patient and encouraging daily supplementation in various ways. A Letter of Medical Necessity can be provided to the patient’s insurance company to assist the patient financially with purchasing supplements. Daily reminders such as pillboxes and phone alarms, may also be helpful in reminding patients of supplementation timing and dosage. Lastly, taking supplements with a small snack or before bed may assist in alleviating supplement-associated nausea.

Special Populations


Due to overall food restriction and/or malabsorption, protein status is a continual concern for all bariatric patients, but especially for the bariatric athlete. In order to preserve and maintain muscle mass, it is crucial to encourage a high-protein diet along with high-quality protein supplements to assist the bariatric athlete in meeting recommended protein needs.3

As with all athletes, hydration before, during, and after physical activity is necessary to prevent dehydration. Sweat and decreased pouch size can hinder bariatric athletes from consuming enough fluid and sodium to replace those lost in sweat during physical activity. To combat dehydration, RDNs should encourage bariatric athletes to choose foods high in both energy and water content, such as Greek yogurt with fruit. RDNs should also encourage patients to consume salty foods after intense exercise to replace sodium losses from sweat.

Bariatric athletes have increased nutrient requirements, and thus are at greater risk of developing deficiencies if adequate intake and vitamin/mineral supplementation are not ensured. Iron deficiency is especially common among bariatric female athletes of childbearing age. A multivitamin with iron or separate iron supplement, along with a high-iron diet, is recommended.

Before beginning to exercise postoperatively, it is necessary for the patient to receive medical clearance. Bariatric patients are instructed to conduct aerobic exercise for 150 minutes per week, with a long-term goal of 300 minutes per week.6,7 In order to help preserve muscle mass, they are also directed to add strength training 2 to 3 times per week.6,7


Bariatric patients are cautioned to avoid pregnancy during the first 18 months after undergoing their procedure. This time frame allows the patient to reach weight loss goals and for their weight to become stabilized. At 18 months post-procedure, regular textures are now tolerable, and patients are able to adhere to their vitamin/mineral schedule, resulting in nutrition-related laboratory values within normal ranges.

The pregnant bariatric patient requires their laboratory values to be reviewed every trimester for possible nutrient depletions, as this patient population is at increased risk of nutrient deficiency. It is often advised that pregnant bariatric patients continue using bariatric specific vitamins rather than an over-the-counter prenatal vitamin. This recommendation is due to the maximal absorption and increased potency of bariatric-specific products sourced from reputable companies.

Renal Patients:

One of the most challenging patient populations to monitor following bariatric surgery are those receiving hemodialysis. To avoid nephrotoxicity, the bariatric dietitian and renal team must collaborate in order to ensure the patient’s nutritional needs are met. Their daily vitamin and mineral schedule must be altered from the standard bariatric regimen secondary to the danger of renal overload of fat-soluble vitamins and magnesium, as well as the loss of water-soluble vitamins during hemodialysis. As with all hemodialysis patients, their sodium, potassium, and phosphorus levels must be closely monitored. Nutritional recommendations for these patients do not follow the standard guidelines created by ASMBS, but are based on the individual patient’s laboratory values. Supplement titrations are to be referred to their nephrologist and renal dietitian.

Key Takeaways

As RDNs, our goal is to assist patients in leading healthier lives through improved dietary techniques and lifestyle changes. Bariatric surgery can be a beneficial tool to aid patients in achieving their weight loss goals and improving their overall health. However, this life-altering surgery is multifaceted, and the most challenging work must be completed by patients themselves. Key points for the bariatric dietitian to enforce with patients include monitoring micronutrient deficiencies, emphasizing portion control, and meeting protein and fluid requirements.

It is essential for bariatric dietitians to educate patients on the specifics of pre- and post-bariatric surgery nutritional guidelines. Even above the indispensable piece of nutrition education, a dietitian must exemplify empathy, encouragement, and emotional support throughout the rigorous bariatric surgery journey.


  1. Mechanick JI, Youdim A, Jones DB, et al. Clinical practice guidelines for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric surgery patient--2013 update: cosponsored by American Association of Clinical Endocrinologists, the Obesity Society, and American Society for Metabolic & Bariatric Surgery. Endocr Pract. 2013;19(2):337-72. doi: 10.4158/EP12437.GL.
  2. 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 ;4(5 Suppl):S73-108. doi: 10.1016/j.soard.2008.03.002.
  3. Raftopoulos I, Bernstein B, O'Hara K, Ruby JA, Chhatrala R, Carty J. Protein intake compliance of morbidly obese patients undergoing bariatric surgery and its effect on weight loss and biochemical parameters. Surg Obes Relat Dis. 2011; 7(6): 733-742. doi:10.1016/j.soard.2011.07.008
  4. Mechanick JI, Youdim A, Jones DB, et al. Clinical practice guidelines for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric surgery patient: cosponsored by American Association of Clinical Endocrinologists, the Obesity Society, and American Society for Metabolic & Bariatric Surgery. Surg Obes Relat Dis. 2013; 9.S159-191. doi:10.1002/oby.20461.
  5. Thibault R, Huber O, Azagury DE, Pichard C. Twelve key nutritional issues in bariatric surgery. Clin Nutr. 2016;35(1):12-7. doi:10.1016/j.clnu.2015.02.012.
  6. Sherf Dagan S, Goldenshluger A, Globus I, et al. Nutritional recommendations for adult bariatric surgery patients: clinical practice. Advances Nutr. 2017;8(2): 382-394. doi:10.3945/an.116.014258.
  7. Adapted from U.S. Department of Health and Human Services. 2008 Physical Activity Guidelines for Americans. Washington (DC): U.S. Department of Health and Human Services; 2008. Available at: Accessed August 6, 2015.