Definition

Bariatric interventions are currently the most effective therapy for obesity. These procedures can be categorized into restrictive, malabsorptive, and combined techniques. The operations are generally performed laparoscopically. According to the SMOB report analyzing data from 2001-2020, gastric bypass was the most common procedure in Switzerland, followed by sleeve gastrectomy ¹. Different procedures are associated with varying risks of malnutrition and micronutrient deficiencies.

Overview of common procedures and expected long-term weight loss ²:

• Laparoscopic Adjustable Gastric Banding (LAGB): 14.9-45.9%
• Sleeve Gastrectomy (SG): 58.3-61.1%
• Proximal Roux-en-Y Gastric Bypass (RYGB): 56.7-67%
• Biliopancreatic Diversion (BPD) with/without Duodenal Switch (DS): 74.1-79%

The goal of these interventions is long-term weight loss and the prevention of complications such as metabolic diseases, joint damage, or sleep apnea syndrome. Additionally, these procedures contribute to the improvement of pre-existing conditions like diabetes or fatty liver disease.

Impact on Nutritional Status

All procedures result in an anatomical alteration of the gastrointestinal tract. This leads to changes in digestion, nutrient absorption, taste perception, the microbiome, and energy metabolism. Consequently, the long-term nutritional status of patients is significantly impacted. There is an increased risk, particularly for protein deficiency with muscle mass loss and micronutrient deficiencies and their consequences ³. In many cases, nutrient deficiencies are already present preoperatively in this high-risk group. Therefore, lifelong micronutrient supplementation, accompanied by regular medical consultations with laboratory monitoring, is essential.

Nutrient Requirements for Post-Bariatric Patients. Adjustments may be necessary for malnourished patients, those with varying physical activity levels, and different age groups. BW = Body Weight; d = Day

Vitamins, Minerals, and Trace Elements ^{3, 5}

• Nutrient deficiencies are common after bariatric interventions, particularly following malabsorptive procedures such as Roux-en-Y gastric bypass ^{5, 9, 10}
• Daily requirements should be covered by oral vitamin supplementation (+ Vitamin B12 via subcutaneous injections)
• LAGB/SG: 100% according to D-A-CH recommendations; RYGB/BPD/DS: 200% according to D-A-CH recommendations
• Potentially critical micronutrients: Vitamins A, D, E, K, B1, B9, B12, C, Copper, Iron, Zinc

Target Levels and Approach in Case of Deficiency

Preventive Supplementation Recommendations

Information not guaranteed.

 

• Coverage of daily requirements via oral multivitamin supplements and additional Vitamin D, Calcium, and Vitamin B12 via subcutaneous injections.
• Increased requirements due to reduced absorption, particularly in RYGB, BPD/DS patients.
• Calcium 1200-1500 mg (after SG and RYGB) and 1800-2400 mg (after BPD); divided into individual supplements with 600-1000 mg, dietary intake, and multivitamin supplements; prefer calcium citrate over calcium carbonate (better absorption).
• Oral calcium helps prevent kidney stone formation by binding oxalate; therefore, it should be continued if calcium oxalate stones develop.
• Vitamin D 2000-3000 IU with target levels >30-50 ng/mL
• Thiamine 12 mg in risk groups (general malnutrition, alcohol use, GI symptoms)
• Supplemental folic acid and possibly zinc for those planning pregnancy or during pregnancy.

Goals of Nutritional Therapy:

• Maintain/Improve nutritional status and body function
• Prevent malnutrition/nutrient deficiencies
• Achieve defined weight targets
• Adapt eating habits to individual needs

Early nutritional therapy plays a central role in maintaining or improving nutritional status. Nutritional screening (Nutritional Risk Screening: NRS 2002 or PG-SGA) should be conducted preoperatively and postoperatively if malnutrition is suspected. Overweight patients already have a high risk of micronutrient deficiency preoperatively. Postoperatively, the risk increases due to anatomical changes that may cause malabsorption, along with initially significantly reduced food intake and often limited food choices. Close interdisciplinary care during this period is essential to maintain good nutritional status.

Preoperative Preparation ^{3, 5, 9}

• Nutritional assessment to estimate malnutrition risk and current nutrient intake, including laboratory monitoring
• The most common deficiencies occur in Vitamin B12, iron, folic acid, Vitamin D, and thiamine
• Obesity is generally associated with Vitamin D deficiency and secondary hyperparathyroidism
• Recommended screening: Thiamine, Vitamin B12, Vitamin A, E, K, zinc, copper
• An untreated preoperative deficiency is associated with metabolic complications
• Preoperative weight loss
• Achieved through a low-calorie diet for 2-6 weeks, up to a maximum of 3 months (studies favor a low-carb over a low-fat diet to improve insulin sensitivity and lipid profile), possibly with the use of a "very-low-calorie diet", e.g., in the form of a formula diet (up to 10% weight loss)
• Reduces peri- and postoperative complications (e.g., bleeding, leaks, infections)
• Associated with improved postoperative weight loss ¹¹
• Improves blood sugar control
• Carbo-loading can be considered immediately before the procedure, which can improve insulin resistance, reduce protein catabolism, and support digestive function postoperatively

Postoperative Care

In the initial postoperative phase, a gradual reintroduction of foods is necessary, starting with a liquid diet and progressing to pureed foods. This phase is followed by the reintroduction of solid foods approximately 10-14 days postoperatively ⁵. Patients should consume multiple small meals throughout the day, gradually increasing the quantity and consistency according to tolerance. The goal is to achieve a healthy, balanced diet. A timely transition to solid foods enhances satiety, supports weight loss, and improves nutrient composition ³.

During follow-up, it's essential to monitor for signs of nutrient deficiencies. Inadequate protein intake, alongside micronutrient deficiencies, is a common complication. Symptoms of protein deficiency may include hair loss, peripheral edema, poor wound healing, or a loss of lean body mass. The choice of protein sources should emphasize high quality, with a focus on foods high in leucine ⁶. Natural food sources are preferred over supplementation with protein powders or similar products. For carbohydrates, complex carbohydrates are recommended ⁷. Fat intake recommendations do not differ from those for the general population and should be adjusted according to the set energy target.

In addition to nutritional therapy, adequate physical activity (150-300 minutes per week, including 2-3 strength training sessions) is crucial for maintaining muscle mass and supporting weight loss. Smoking should be avoided, and alcohol consumption kept to a minimum. For those at an elevated risk of nutrient deficiencies and dehydration, complete fasting (e.g., for religious reasons) should be avoided during the first 12-18 months. Additionally, in cases of increased risk for osteoporosis, a bone density scan should be conducted every two years ⁹.

Whenever possible, the energy and protein requirements should be met through oral nutrition. If needs cannot be met through enriched foods, snacks, or oral nutritional supplements, complementary enteral nutrition should be initiated after no more than 5-7 days. Parenteral nutrition is indicated if, despite enteral nutrition, protein malnutrition and/or hypoalbuminemia persists.

Oral Nutrition

Practical Recommendations (if indicated):

• 4-6 small meals daily
• Eat slowly and chew well; stop eating when feeling full
• Focus on balanced meals with a high protein content ⁴
• Ensure adequate fluid intake (≥1.5 liters/day), separate from meals (15 minutes before, 30 minutes after)
• Daily micronutrient supplementation is essential.

Enteral and Parenteral Nutrition

Artificial nutrition is rarely necessary in post-bariatric patients. However, in cases of severe malnutrition, additional nutritional therapy may be indicated. Gastrointestinal issues or postoperative complications, such as leaks, bleeding, or persistent vomiting, may also necessitate enteral or parenteral nutrition. A hypocaloric diet with a high protein/amino acid content is recommended ¹².

Monitoring

• Lab monitoring: 3 months postoperatively, then every 6-12 months
• Recommended parameters: Blood count, electrolytes, lipid profile, liver and kidney function, vitamin and mineral status (e.g., iron, serum B12, and if necessary, methylmalonic acid, folic acid, potentially thiamine; for malabsorptive procedures like RYGB: zinc and selenium, potentially copper/ceruloplasmin).

Special Considerations ^{3, 7}

Early Dumping Syndrome

• Occurs 15-60 minutes post-meal, due to rapid gastric emptying; shifts fluid from intravascular space to the intestinal lumen, causing cardiovascular symptoms and triggering gastrointestinal and pancreatic hormone release.
• Symptoms: Abdominal pain, diarrhea, nausea, dizziness, flushing, palpitations, tachycardia, hypotension, syncope.
• Prevalence: 40-76% after RYGB and 30% after SG.
• Nutritional intervention: Small meals, avoid simple carbohydrates, combine complex carbohydrates with protein and dietary fiber in one meal, separate liquids from meals.
• Medication: Somatostatin analogs, e.g., Octreotide.

Late Dumping Syndrome

• Occurs 1-3 hours post-meal due to hypoglycemia from hyperinsulinemia.
• Often develops 2-9 years postoperatively.
• Symptoms: Sweating, hunger, palpitations, neuroglycopenia (confusion, dizziness, visual disturbances, syncope, tremors).
• Nutritional intervention: Avoid simple carbohydrates, consume complex carbohydrates and combine with protein; consider simple carbohydrates 1-2 hours after meals to correct hypoglycemia (max. 10 g glucose).
• Medications: Acarbose, somatostatin analogs, diazoxide.

GI Symptoms

• Symptoms such as fullness, constipation, or bloating are common.
• Diarrhea can indicate secondary exocrine pancreatic insufficiency (due to reduced postoperative stimulation).
• Nutritional intervention: Lactose-free diet if indicated, adequate fluid intake, eat slowly and chew well, increase dietary fiber.
• Medication: Probiotics, pancreatic enzymes, symptomatic treatment, dietary fibers.
• Nausea and vomiting are more common in the early weeks and are usually due to improper eating behavior.
• For persistent vomiting, consider a neurological evaluation and thiamine supplementation—even before laboratory confirmation of a deficiency ⁵

Dehydration

• Responsible for about a third of hospitalizations in the first three months post-surgery ¹³
• Main causes: Vomiting, reduced food and fluid intake, often due to taste changes (avoidance of water).

SIBO (Small Intestinal Bacterial Overgrowth)

• Caused by reduced stomach acid and/or altered gastrointestinal anatomy.
• Symptoms: Ranges from asymptomatic to abdominal pain, diarrhea, dyspepsia, weight loss, bloating.
• Diagnosis: H2 breath test.
• Nutritional intervention: Low-FODMAP diet.
• Medication: Antibiotics (e.g., Rifaximin), probiotics.
• High risk of recurrence, so antibiotic treatment should be carefully considered.
• Affects nutrient absorption, such as vitamin B1, B12, or fat-soluble vitamins.

Osteopenia/Osteoporosis

• Increased risk of fractures and osteoporosis due to rapid weight loss and micronutrient deficiencies (vitamin D and calcium).
• Nutritional intervention: Regular intake of micronutrient supplements.
• Bone density scan every two years.

Pregnancy

• Recommendation to wait 12-18 months postoperatively before becoming pregnant ⁸
• Requires balanced diet and stable nutrient supply.
• Classified as a high-risk pregnancy: increased risk for preterm birth, small-for-gestational-age infants, and gastrointestinal issues.
• Close interdisciplinary monitoring is essential.
• Ideally, broad micronutrient monitoring pre-conceptionally and correction of any deficiencies.
• Additional supplementation: 800-1000 µg folic acid, replace vitamin A with β-carotene.

Eating Disorders

• Many obese individuals have preoperative eating disorders, such as binge-eating disorder.
• Normalizing eating behavior is crucial for long-term weight loss success following bariatric surgery.
• Postoperatively, severe binge eating is not feasible due to the reduced stomach volume, which can make adjusting eating behavior particularly challenging for some patients.
• Psychological support is recommended ⁵