Preoperative Very Low Energy Diet (VLED) for Bariatric Surgery

Very lowenergy diets (VLEDs) are structured dietary regimens that provide 400800kcalday1, typically through commercially prepared liquid or semisolid formulas. They are increasingly used in the weeks before bariatric surgery to improve operative safety and postoperative outcomes.

Why a VLED Before Surgery?

• Liver size reduction: A fatty liver can occupy up to 30% of the abdominal cavity. A 2week VLED can shrink liver volume by 1525%, creating more working space for the surgeon.
• Decrease intraabdominal pressure: Less liver bulk translates into lower intraabdominal pressure, reducing the risk of bleeding and organ injury.
• Improved metabolic control: Rapid weight loss improves insulin sensitivity and glycaemic control, especially important for patients with type2 diabetes.
• Enhanced patient motivation: Seeing early weight loss can boost confidence and adherence to the postoperative diet.

Typical Protocol

Most centres prescribe a VLED for 24weeks before the scheduled operation. The exact duration depends on baseline liver size, comorbidities, and patient tolerance.

1. Product selection

Commonly used formulas include:

• Proteinonly shakes (e.g., Optifast, ProSure)
• Lowcarbohydrate, highprotein soup blends
• Modified mealreplacement bars for occasional solid intake

2. Calorie distribution

Typical macronutrient split: 35% protein, 35% carbohydrate, 30% fat. Protein provision is usually 1.21.5gkgideal body weight to preserve lean mass.

3. Monitoring

• Baseline and weekly weight check.
• Blood tests at start and end (electrolytes, renal function, liver enzymes, HbA1c).
• Assessment for dehydration, constipation, or intolerance.

Evidence Summary

Systematic reviews and randomized trials have consistently shown that a preoperative VLED leads to:

• Average liver volume reduction of 1822% (p<0.01).
• Shorter operative time (mean 1520min less).
• Lower intraoperative blood loss (30ml reduction).
• No increase in perioperative complications when properly supervised.

[1] R. Chang et al., Preoperative VLED and liver size in bariatric patients,Surg Obes Relat Dis, 2022.

[2] C. B. Scopinaro et al., Impact of preoperative diet on surgical outcomes,Obes Surg, 2020.

Practical Tips for Patients

1. Stay hydrated: Aim for at least 2L of water daily; add electrolytes if recommended.
2. Eat slowly and chew thoroughly: Even liquid meals can cause discomfort if consumed too quickly.
3. Watch for warning signs: Dizziness, severe nausea, or dark urine require immediate medical review.
4. Plan meals around the clock: Typical schedule three 200ml shakes plus one small snack each day.
5. Maintain physical activity: Light walking or stretching helps preserve muscle mass.

Potential Risks & Contraindications

While VLEDs are safe for most patients, they are not suitable for:

• Pregnant or lactating women.
• Severe renal impairment (eGFR<30ml/min/1.73m).
• Uncontrolled electrolyte disorders.
• Patients with a history of eating disorders without specialist supervision.

Common sideeffects (usually mild) include constipation, transient headache, and metallic taste.

Transition to Postoperative Diet

After surgery, the VLED is typically phased out over 12weeks, moving to a proteinrich, lowcalorie solid diet (e.g., 60g protein per day, 500800kcal). The rapid shift is easier because the gastrointestinal tract is already accustomed to a reduced volume of intake.

Key Takeaways

• A short preoperative VLED is an evidencebased strategy to shrink liver volume and improve operative conditions.
• Proper selection of formula, regular monitoring, and patient education are essential for safety.
• The diet should be individualizedduration and calorie level adjusted to patient needs and comorbidities.
• When implemented correctly, VLED does not increase complication rates and may enhance early weightloss outcomes.

For more detailed protocols or to enrol in a preoperative diet program, please contact your bariatric surgery centre.