Why a liquid diet before bariatric surgery?

Steph Wagner MS, RDN

January 19, 2024

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Berry Cream Protein Shake | Bariatric Liquid Diet | FoodCoach.Me
Berry Cream Protein Shake

You’ve probably noticed by now…every bariatric program is DIFFERENT. Some programs will require a liquid diet before surgery, but another program might require weight loss before surgery.

It’s super confusing when your sister had surgery down the street and her doctor tells her different information then yours. What gives?!

Having gone through a recent pregnancy, I’m reminded that it’s not a one size fits all when it comes to doctors recommendations. My friend’s doctor prescribed her something for nausea¬†while my doctor didn’t recommend that drug. Why are the guidelines so different!?

Clinical judgement and different medical approaches

The recommendations are different because doctors are different. They are also different because bariatric surgery is a new-ish field AND research is always changing the way we do things.

One major difference between programs is whether or not you have a pre-op diet OR a pre-op weight loss requirement.

One bariatric surgeon may ask you to lose 5-10% of your starting weight. This might be 15-30 pounds for you. It could be more, it could be less. This can be deflating when you think “I’m here because I can’t lose weight, and now this doctors wants me to lose weight before the surgery?”

Another doctor may say “you don’t need to lose weight but we recommend you don’t gain anything.” But, as surgery nears you start hearing about a 2 week liquid diet before surgery.

For those of you keeping score, that could ean you have a 1-2 week liquid diet after surgery too…now you are looking at up to 4 weeks of protein shakes and water. YIKES.

Why all the liquids? Is that even healthy?

It’s a different approach to the same thing. Your doctor wants to shrink the size of your liver to make for an easier operation. Many studies show pre-op weight loss speeds up your recovery time and make surgery safer. Liquid diets that shrink the liver will allow for a shorter operation time, which leads to a faster recovery.

Some surgeons will require more weight loss or a more restrictive pre-op diet for a higher BMI. Patients with a BMI of 50 or more might have more prep for a safe surgery than patients with a BMI above 40.

Whether you’re asked to lose 5-10% of your weight during your 3-6 months of supervised weight loss visits OR you are put on a 2 week pre-op diet, they both have their pros and their cons.

My preference is to lose weight over the course of your pre-op season. It helps you stay focused on the upcoming surgery and allows you to start making the changes you inevitably need to make to be successful. But. I’m not your doctor :)

If you are thinking of having a weight-loss surgery, this would be a great question to ask of the program you’re considering! While you’re at it, ask if they have a dietitian on staff to help you with the pre and post-op nutrition. Some clinics have a dietitian on site and others will refer out. Sometimes it’s more about what you have access to, but if you can find a clinic that has providers in one spot it does enhance your care.

All my best,


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