Bariatric Pre op Diet

The Complete Guide to Bariatric Surgery Pre-Op Diets

Preparing for bariatric surgery requires dedication, discipline, and significant changes to your lifestyle. A critical part of that preparation is the pre-operative diet, typically started 2-4 weeks before your scheduled surgery date. This intense diet jumpstarts weight loss prior to surgery, while shrinking your liver size to ensure the operation can be conducted as safely and effectively as possible. Some bariatric surgeons recommend the low calorie diet, but some also will recommend an all-liquid diet for the 2 weeks immediately leading up to surgery. This guide is here to show you a typical pre-op diet, but be sure to strictly follow your physician and surgeon's recommendations.

What Exactly is a Pre-Op Diet?

A bariatric surgery pre-operative diet refers to the strict meal plan that must be followed in the weeks leading up to your procedure. The purpose of this diet includes:

  • Shrinking the size of your liver - This gives the surgeon clearer access and visibility during the operation for your safety. It also reduces risk of complications.
  • Initiating quick weight loss - Losing some excess pounds before surgery jumpstarts your weight loss journey and makes the procedure simpler for the surgical team.
  • Improving surgical outcomes - Appropriately preparing with the pre-op diet helps lead to better results long-term post-surgery.
  • Evaluating your ability to follow recommendations - Your commitment to the pre-op diet also shows your healthcare team how compliant you can be following surgery guidelines. This is indicative of your likely capability to achieve sustainable success in the future after your operation.

The typical bariatric pre-surgery diet is very low in calories, carbohydrates, sugars, and fats. It instead prioritizes high protein, nutrient-dense foods without excess calories. Portion control is also strict. But following these guidelines before surgery can truly pay off after your procedure and lead to effective long-term weight loss.

bariatric patient talking to doctor about bariatric pre op diet


When Should You Start the Pre-Op Diet?

Most bariatric surgery programs will instruct patients to begin the structured pre-operative diet 1-2 weeks prior to the scheduled procedure. However, some clinics are moving towards longer pre-op diet periods of 4-8 weeks before surgery in certain cases, and then switching to liquid only diet around 1 week before surgery.

Why start so soon?

Beginning the diet earlier continues weight loss momentum and ensures the liver is not enlarged for a safer operation. It also assesses how well you can stick to strict nutritional guidelines long-term.

Starting too late reduces the diet's effectiveness for surgical preparation and doesn't allow enough time for the clinician to observe your compliance.


Pre-Op Diet Basics: What You Can Eat

The bariatric pre-op diet focuses on specific types of foods to shrink your liver while providing important nutrients. Here’s an overview of what a typical daily meal plan looks like:

  • Protein goal: At least 60-80 grams of high quality lean protein per day. Great options include eggs, chicken, turkey, fish, shellfish, tofu, low-fat dairy, and bariatric protein shakes/powders.
  • Vegetables: Fill half your plate with low starch vegetables including broccoli, spinach, carrots, zucchini, peppers, and greens. Go easy on high sugar veggies like corn and potatoes.
  • Fruits: Stick to lower sugar fruits in small portions like berries and green apples. Avoid bananas, grapes, pineapple and other sweeter fruits.
  • Grains: Avoid processed refined grains like bread, rice, pasta and baked goods. Small amounts of whole grains like brown rice or quinoa may be allowed.
  • Fats & oils: Include small amounts of healthy fats like olive oil, avocado, nuts, seeds, and nut butters. Avoid fried foods and fatty cuts of meat.
  • Beverages: 64+ ounces of calorie-free liquids like water, unsweetened tea, black coffee, and protein shakes. Stay away from alcohol, juice, soda, and other sugary drinks.
  • Daily calories: 1000-1200 calories total, made up of high protein low refined carb foods & veggies primarily. Portions will seem very small to stay in this strict calorie range.
Bariatric Preop Diet

Prepping with an All-Liquid Diet

Some bariatric surgery programs take the pre-op diet a step further by requiring an all-liquid meal plan 3-5 days immediately before surgery. This intense "liquid diet" has all the same goals of shrinking the liver, initiating weight loss, and evaluating patient compliance.

Here are the key characteristics of a typical pre-op liquid diet:

  • Usually 3-5 days in length, starting after your last pre-op clinical appointment
  • Drastically low in calories, carbs, fats to accelerate liver shrinkage
  • Strictly liquid-only foods including:
    • Protein shakes & dairy-free liquid meal replacements
    • Low sodium broths and consommés
    • Sugar-free gelatin and popsicles
    • Small amounts of unsweetened juice diluted with water
    • Decaf tea/coffee and calorie-free beverages
  • Provides fast results but can be challenging for hunger levels
  • Easing symptoms via hot liquids, protein priority, and small frequent "meals"

Think of this liquid diet period as the final preparation push before surgery after completing the standard 2+ week pre-op eating plan. While difficult, embracing the all-liquid days helps ensure surgical success!


Check out this guide to learn more about an All-Liquid Bariatric Pre-op Diet


Bariatric Preop Liquid Diet


Supplements and Support for Success

To meet micronutrient needs on such a strict diet, bariatric patients take supplements even before surgery. Follow your clinic’s advice, but common recommendations include:

  • Multivitamin: Essential to provide enough vitamins and minerals when drastically reducing intake. Choose a complete formula made for bariatric patients.
    Bariatric Multivitamin
  • Calcium citrate: 1000-1200 mg daily helps support bone health and metabolism. Stomach acid reduction after surgery inhibits calcium absorption, so citrate forms are preferred.
  • Vitamin D: 3000 IU per day minimum aids calcium absorption and immunity. Deficiency is extremely common after bariatric procedures.
  • Iron: Anemia risk increases after surgery, so iron may be recommended. Take in separate doses from calcium as they interfere with absorption.
  • B-Complex: Supports energy, metabolism, nerve health and more. Specific B12 supplementation is also commonly advised.


Check out this article to learn about the Top Recommended Bariatric Multivitamins

Best Bariatric Multivitamins

Additional Ways to Support Yourself

The pre-op diet is challenging. Here are tips to stay on track:

  • Meal prep your weekly meals to remove temptation
  • Join an online or in-person bariatric support community
  • Consider working with a dietitian or nutrition coach
  • Explore recommended recipes from your surgical clinic
  • Remind yourself constantly of why you are doing this!

Staying focused on your end goal of long-term improved health will give you the motivation you need. You’ve got this!

Author: Carrie H.

Carrie is a passionate health and nutrition writer who transforms complex medical research into accessible, evidence-based content to empower readers to make informed choices about their wellbeing. With a background in science and a dedication to helping others live healthier lives, she provides thoughtful analysis of the latest studies and practical, actionable advice readers can apply to their own lives.

Reviewed By: Dr. Kevin Huffman

Dr. Huffman is an accomplished board-certified bariatric physician with extensive clinical experience and expertise in treating obesity. He has trained countless healthcare providers and founded American Bariatric Consultants to develop highly sought-after protocols, training materials and continuing education used widely by medical societies, hospitals and physicians. Dr. Huffman's impact reaches far beyond direct patient care, as he actively prepares the next generation of physicians to achieve board certification in bariatrics, thereby exponentially expanding access to this vital medical treatment.

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