Pre-Operative Liquid Diet Before Having Bariatric Surgery

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Bariatric surgery helps morbidly obese individuals lose weight by restricting food intake. There are different types of surgeries, but they all involve dividing the stomach to reduce the amount of food you can consume. Gastric bypass surgery is a major operation and does carry some risks. Following your doctor-ordered pre-op diet helps minimize surgical risk and shorten recovery time, while preparing you for your new post-op way of eating.

Gastric Bypass Basics

A common type of bariatric surgery is the Roux-en-Y gastric bypass, or RYGB, which not only reduces the size of your stomach, but limits calorie absorption by bypassing the stomach, duodenum, and upper intestine; your new stomach is connected directly to your small intestine. After surgery, your new stomach may only hold a few tablespoons of food. Over time, your stomach -- also called your "pouch" -- may stretch, allowing you to consume about 1 cup of food at a time -- still far less than the 4 cups a normal stomach can hold. To maintain your weight loss you'll still need regular exercise and healthy eating habits.

Diet Before Surgery

Most surgeons require a strict diet before surgery. Losing as much fat as possible, especially abdominal fat, decreases surgical risk. Depending on the type of surgery you're having, your pre-op diet may start three weeks or three months before surgery. Your doctor may not be require you to be on a liquid diet that entire time, but it's common to be on a liquids-only diet for the last two weeks before your operation. This diet is typically low-calorie, often between 800 and 1,200 calories. Generally, you drink sugar-free, low-carb shakes high in protein. Protein helps preserve lean muscle mass and can help you recover after surgery. Expect to consume between 70 and 120 g of protein daily.

Following Your Pre-Op Diet

Changing your diet before surgery prepares you both physically and mentally for your new post-op lifestyle. Your willingness and ability to follow through with the recommendations made by your health care team and to carry out prescribed changes in your diet and exercise routine also help determine if gastric bypass surgery is right for you. Your doctor may postpone surgery if you don't make the necessary changes. Your diet before surgery also prepares you for your post-op diet, which limits carbs, fat and sugar.

Non-Liquid Pre-Op Diet

If you are allowed to start with a whole foods diet before progressing to a liquids-only diet, you shouldn't drink any alcoholic beverages; you should limit sweets including soda, limit carbohydrates -- especially refined grains and starchy vegetables, choose low-fat rather than full-fat dairy products, limit saturated and trans fats from fried foods and avoid binge eating. If you smoke, you should stop. Your diet should consist of lean meats, seafood, eggs, vegetables, fruit and limited high-fiber grains such as oatmeal. You may need to add a protein supplement to increase your protein intake without adding too many more calories.


If you do not completely adhere to the restricted pre-operative diet, inform your doctor right away. Your surgeon may recommend postponing your surgery to reduce any surgical or anesthesia risks.