Overview
31
Grade A
Very strong
Very strong
42
Grade B
Strong
Strong
72
Grade C
Not strong
Not strong
101
Grade D
Expert opinion
Expert opinion
Patient eligibility criteria
BMI ≥40 kg/m²
No comorbidities required Grade A
BMI ≥35 + ORC
One or more severe obesity-related complications Grade C
BMI 30–34.9
T2D with inadequate glycaemic control Grade B
Asian patients
Adjust cutoffs: overweight ≥23, obesity ≥25 kg/m² Grade D
Waist circumference
Measure all patients esp. when BMI <35; ethnic-specific cutoffs apply
Evidence grade distribution
Key 2019 updates relevant to dietitians
New (R4)
Ethnicity-specific BMI adjustments incorporated into eligibility
New (R13)
Lifestyle medicine checklist required as part of medical clearance for all candidates
New (R34–36)
ERABS (Enhanced Recovery After Bariatric Surgery) protocols — prehabilitation and carbohydrate loading
New (R67)
Commercial supplement quality: many products adulterated/mislabelled — advise USP-verified brands
New (R70–71)
Close monitoring of diabetes medication and thyroid hormone dosing post-op
New (R73)
GERD management after sleeve gastrectomy — PPI therapy; conversion to RYGB if refractory
New (R76)
Anastomotic ulcer prophylaxis: PPI 90 days to 1 year post-RYGB depending on risk
RD role
Mandatory consultation pre- and post-op. Diet progression, supplement monitoring, follow-up coordination. Grade A, BEL 1
Bariatric procedures
Four primary procedures endorsed by ASMBS. Laparoscopic approach preferred over open (lower morbidity and mortality).
Sleeve gastrectomy
SG / LSG
25–30%
Total body weight loss
Most performed (58%)
No anastomosis
Fewer nutrient deficiencies vs RYGB
Versatile for high-risk populations
GERD risk 20–30%
Leaks difficult to manage
Limited data beyond 5 years
Roux-en-Y gastric bypass
RYGB / LRYGB
30–35%
Total body weight loss
Strong metabolic effects
Effective for GERD
Standardised technique
<5% major complication rate
Long-term micronutrient deficiencies
Internal hernias possible
Marginal ulcer risk
Biliopancreatic diversion / duodenal switch
BPD/DS
35–45%
Total body weight loss
Highest weight loss
Very strong metabolic effects
Durable long-term
Highest deficiency risk
3–5% protein-calorie malnutrition
Technically challenging
Laparoscopic adjustable gastric band
LAGB
20–25%
Total body weight loss
Reversible & adjustable
No anatomic alteration
Lowest complication rate
High explant rate
Declining use (3.5% of procedures)
High re-operation rate
US procedure prevalence (2016)
Weight loss by procedure
T2D remission rates
BPD/DSHighest remission
RYGB~72% at 2 years → ~30% at 15 years
SGComparable to RYGB short-term
LAGBLowest; requires significant weight loss first
Note"Remission" not "cure" — T2D returns in >50% within 10 years
Nutrition & supplementation
Minimum daily supplementation by procedure
| Supplement | LAGB | SG | RYGB | BPD/DS | Grade |
|---|---|---|---|---|---|
| Multivitamin + minerals containing iron, folate, thiamine — chewable initially |
1 tablet | 2 tablets | 2 tablets | 2 tablets | B |
| Calcium (elemental, as citrate) in divided doses; citrate preferred — can take without food |
1200–1500 mg | 1200–1500 mg | 1200–1500 mg | 1800–2400 mg | B |
| Vitamin D titrate to 25-OH-D >30 ng/mL; D3 preferred over D2 |
≥2000–3000 IU/day (all procedures) | A | |||
| Iron (elemental) separate from calcium; add Vitamin C to enhance absorption |
18 mg | 45–60 mg | 45–60 mg | 45–60 mg | A |
| Vitamin B12 sublingual, disintegrating tablet, liquid or IM |
350–1000 µg/day oral OR 1000 µg IM monthly | B | |||
| Thiamine (B1) ≥12 mg/d all; 50–100 mg/d in high-risk groups |
≥12 mg/day via multivitamin (minimum) | C | |||
| Zinc ratio: 8–15 mg zinc per 1 mg copper supplemented |
8–11 mg | 8–11 mg | 8–22 mg | 16–22 mg | C |
| Copper gluconate or sulfate preferred source |
1 mg | 1 mg | 2 mg | 2 mg | D |
| Vitamin A water-miscible form for malabsorptive procedures |
5000 IU | 5000–10000 IU | 5000–10000 IU | 10000 IU | D |
| Folate 800–1000 µg/day for women of childbearing age |
400–800 µg/day via multivitamin | B | |||
Nutrient deficiency risk
Folate
Up to 65% post-op. Screen all patients. Extra attention for childbearing-age women.
Very high
Vitamin D / Ca
Up to 100% of patients. Routine screen all. 25-OH-D is preferred assay.
Very high
Iron
LAGB 14%, SG <18%, RYGB 20–55%, BPD 13–62%. Can occur despite routine supplementation.
High
Vitamin A
Up to 70% within 4 years post-RYGB & BPD/DS. Screen first post-op year.
Moderate–high
Zinc
BPD/DS up to 70%, RYGB up to 40%, SG up to 19%. Annual screen after RYGB & BPD/DS.
Moderate
Copper
BPD/DS up to 90%, RYGB 10–20%. Annual screen even without symptoms.
Moderate
Vitamin B12
RYGB <20%, SG 4–20% at 2–5 yrs. Screen annually; q3 months first year.
Moderate
Thiamine (B1)
<1–49% depending on procedure and timeframe. Screen high-risk groups.
Variable
Vitamin E / K
Uncommon. Screen only if symptomatic (haemolytic anaemia, excessive bleeding).
Low
Protein targets
Minimum60 g/day
Standard targetUp to 1.5 g/kg ideal body weight/day
High-need (individualised)Up to 2.1 g/kg IBW/day
GuidanceIndividualised by RD per gender, age, and weight. Grade D
Fluid goals
Daily minimum>1.5 L/day
Timing30 min before or after meals; sip slowly
Early post-opAt least 60 oz (1800 cc) daily within days of surgery
Deficiency deficiency chart
Post-operative diet progression
Staged progression supervised by an RD. Timing may vary by surgeon, institution, and patient tolerance. Patients not progressing on schedule should be evaluated for anastomotic ulcer, stricture, or obstruction.
Diet stages
Day 0–1 · Stage 1
Clear liquids
Sugar-free, low-calorie. Begin night of surgery. ~400 kcal/day. Sip slowly. Avoid caffeine, carbonation, alcohol. Emphasise hydration.
Days 1–14 · Stage 2
Full liquids
Sugar-free/low-sugar. Include protein sources (25–30 g/serving). Advance from POD 1–3. Minimum 60 oz (1800 cc) daily. Continue 10–14 days.
~2 weeks · Stage 3
Pureed / soft texture
Food requiring no chewing. Soft, moist, diced, ground, or pureed protein sources 3–5×/day. Continue for ~1 week then advance.
~3–4 weeks · Stage 4
Mechanically altered soft
Minimal chewing required. Chopped, ground, mashed. Progress to solids 600–800 kcal/day by weeks 3–4.
~6–8 weeks · Stage 5
Regular solid foods
Most solid foods tolerated. Begin with only a few bites. Avoid bread/rice/pasta until protein and vegetable goals are met consistently.
6 months+ · Long-term
Balanced maintenance diet
1200–1500 kcal/day target; ~1500–1800 kcal/day at 6 months. ≥5 servings fruit & vegetables daily. Avoid concentrated sweets (especially RYGB).
Eating behaviour principles
Meal pattern3 small meals per day. No grazing.
ChewingChew thoroughly to smooth consistency before swallowing
SatietyStop eating as soon as satiety is reached
Fluids & mealsNo drinking during meals; wait 30 min after eating before resuming fluids
AvoidConcentrated sweets, carbonated beverages, fruit juice, high-fat fried foods, alcohol (early stages), caffeine (early stages)
RYGB specificEliminate concentrated sweets to minimise dumping syndrome
MedicationsUse crushed or liquid rapid-release formulations early post-op for maximal absorption
Caloric intake over time
Long-term dietary guidance
Fruit & vegetables≥5 servings/day for fibre and phytonutrients
BPD/DS dietSmall, nutrient-dense meals high in protein; include fruits, vegetables, whole grains, omega-3s; avoid concentrated sweets
LAGB long-termGenerally resume normal diet soon after surgery; frequent band adjustments needed
Simple sugarsLimit to <10% of daily caloric intake (all procedures)
Follow-up & monitoring
Follow-up schedule by procedure
| Item | LAGB | SG | RYGB | BPD/DS |
|---|---|---|---|---|
| Visit schedule initial, then intervals until stable | 1, 1–2, 12 mo | 1, 3, 6, 12 mo | 1, 3, 6–12 mo | 1, 3, 6 mo |
| SMA-21 & CBC | Every visit (with iron studies at baseline and as needed) | |||
| Iron studies | Within 3 months post-op, q3–6 months to 12 months, then annually | |||
| Vitamin B12 MMA ± homocysteine optional for metabolic deficiency | Annually (q3 months first year) | |||
| Folate, 25-OH-D, iPTH | — | — | Annually | Annually |
| Vitamin A | — | — | Optional | Initially + q6–12 mo |
| Zinc, Copper, Selenium | If clinical findings | If clinical findings | Annually | Annually |
| Thiamine | If symptomatic or risk factors present | |||
| HbA1c & TSH | Long-term follow-up | |||
| Bone DXA | At 2 years post-op | |||
| 24 h urinary calcium | — | — | — | 6 months then annually |
| Lipids | q6–12 months based on risk and therapy | |||
| Lifestyle medicine eval | Each visit — eating index, fitness, sleep, alcohol, substance use, community | |||
Physical activity goals
Minimum aerobic150 min/week moderate-intensity Grade A, BEL 1
Target aerobic300 min/week
Strength training2–3 sessions per week
TechnologyWearables and activity monitors recommended — positive effect on physical activity behaviours Grade B
Sarcopenia riskWeight loss (esp. bariatric) increases skeletal muscle loss — resistance training is essential
Weight regain evaluation
Step 1Assess dietary adherence with lifestyle modification
Step 2Evaluate medications associated with weight gain or impairment of weight loss
Step 3Assess for maladaptive eating behaviours and psychological complications
Step 4Radiographic or endoscopic evaluation (pouch enlargement, anastomotic dilation, gastrogastric fistula, band issues)
Intervention orderDietary change → PA → behavioural therapy → pharmacotherapy → surgical revision
Support & adherence strategies
Support groupsEncourage participation in ongoing support groups Grade B
Self-monitoringDaily self-weighing with smart scales linked to improved weight-loss outcomes Grade B
Mobile technologyText messaging, e-mail, diet tracking apps, virtual reality software — strong RCT evidence Grade B
TelemedicineUse to reduce follow-up attrition (up to 89% attrition reported without active retention strategies)
PregnancyAvoid for 12–18 months post-op. If pregnant, screen every trimester for iron, folate, B12, vitamin D, calcium (+ fat-soluble vitamins after malabsorptive procedures)
Clinical red flags
Alerts for dietitians in post-bariatric follow-up. Items marked with a danger indicator require urgent clinical escalation.
Urgent
Wernicke encephalopathy risk: Suspect thiamine deficiency in any patient with nausea/vomiting, neuropathy, encephalopathy, or visual changes post-op — including after purely restrictive procedures (LAGB, SG, IGB). Treat before lab confirmation. IV thiamine 500 mg/day × 3–5 days, then 250 mg/day × 3–5 days, then 100 mg/day orally indefinitely. Intramuscular if IV unavailable.
Severe protein malnutrition / hypoalbuminaemia: Unresponsive to oral or enteral protein supplementation → consider parenteral nutrition. PN formulation should be hypocaloric with relatively high nitrogen (1.2 g/kg actual or 2–2.5 g/kg ideal weight amino acids). Monitor closely for refeeding syndrome (BPD/DS especially).
Monitor closely
Weight regain or plateau: Comprehensive evaluation of dietary adherence, weight-gain medications, maladaptive eating (binge eating, grazing, night eating), psychological factors, and structural changes. Intervene with dietary modification + PA + behavioural therapy before pharmacotherapy or surgical revision.
Post-bariatric hypoglycaemia: Confirm postprandial hypoglycaemia with symptoms. First-line dietary management: low-carbohydrate, low-glycaemic index diet with adequate protein and heart-healthy fats; restrict alcohol and caffeine. Most patients respond to dietary modification or pharmacological intervention before surgical options are needed.
Persistent nausea, vomiting, or dysphagia: If diet stages are not progressing — suspect anastomotic ulcer, stricture, or mechanical obstruction. Alert surgical team promptly. Also a major trigger for thiamine depletion; consider empiric thiamine supplementation.
De novo GERD after sleeve gastrectomy: Treat with PPI. If refractory, consider conversion to RYGB. Proton-pump inhibitor use can interfere with calcium absorption — monitor bone health accordingly.
Practice points
Zinc–copper interaction: For every 8–15 mg elemental zinc supplemented, add 1 mg copper to prevent copper deficiency — especially critical in patients supplementing zinc for hair loss or deficiency. Copper deficiency can cause anaemia, neutropenia, and myeloneuropathy.
Folate masking B12 deficiency: Supplementing >1 mg/day folate can mask B12 deficiency (and B12 status should not be assumed from serum B12 alone — check methylmalonic acid ± homocysteine). Always assess B12 in patients on higher-dose folic acid.
Supplement quality: Many commercial bariatric supplement products are adulterated or mislabelled (R67). Advise patients to use USP-verified products, or brands reviewed by their healthcare professional. Discuss all supplements at every consultation.
NSAIDs contraindicated post-op: Associated with anastomotic ulcers, perforations, and leaks (Grade C). If unavoidable, add PPI cover. Educate patients proactively before discharge and at follow-up — written notification alone is ineffective.
Pregnancy after bariatric surgery: Advise avoiding pregnancy for 12–18 months post-op. If pregnancy occurs, screen every trimester for iron, folate, B12, vitamin D, and calcium — plus fat-soluble vitamins (A, E, K) and zinc/copper after malabsorptive procedures. Vitamin A is teratogenic in excess; monitor carefully.
Alcohol use disorder: Alcohol metabolism is altered after SG and RYGB — faster peak blood alcohol concentrations, underestimation by breath analysers. High-risk groups should be advised to eliminate alcohol consumption post-op. Assess at every follow-up visit.