How much water after Gastric Sleeve or Bypass

Steph Wagner MS, RDN

August 9, 2022

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How much water after Gastric Sleeve or Bypass

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Water is essential after gastric sleeve, bypass or duodenal switch

You may have heard water after gastric sleeve or bypass (or DS, SIPS/SADI or other bariatric surgeries) is a HUGE deal. Why?

Water is a macronutrient. Yes, a macro!

If you’ve heard anything about macros, you might think of protein, carbohydrate and fat. Which would be true.

But the fourth macro is water. Water is one of the body’s essential nutrients. Every cell in your body needs water.

Water is also a natural appetite suppressant. Our brains confusing hunger cues and thirst cues. It is very common we mistake our need for water for hunger. Staying hydrated allows you to understand your body cues.

Hydration also helps you burn fat more efficiently. The kidneys need water to work properly and without water they put some of their work onto the liver. One of the livers main functions is to metabolize (or burn) fat. If it takes on work from the kidney, it can’t focus on its burn burning job as effectively.

Drinking plenty of water will also help with constipation and with water retention.


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Dehydration is the number one reason for readmission to the hospital after bariatric surgery

You may have been told this in your pre-op classes and it is TRUE! Water after Gastric Sleeve or Bypass is super, super important.

The good news is, the most common reason why someone needs to go back is easily fixed. There are a few reasons why patients get dehydrated after surgery.

It is hard to get in a lot of water with a healing, inflamed stomach.

If you are experiencing post-op nausea, liquids are a challenge to drink.

You aren’t eating as much and food contains water.

The biggest trick, in my experience, is when someone starts to get behind on water.

It reminds me of staying ahead of pain control. If you get behind on medication after surgery to control pain, it can be really hard to get pain back down to a comfortable level.

Our body doens’t hit ‘reset’ at midnight. If you were behind on water on Tuesday, you go into Wednesday low in water. If that trend continues, mild dehydration can make you feel a little nauseated.

Water can start to sound worse when you are dehydrated. Which is problematic because you need water!

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How much water to drink after Gastric Sleeve or Bypass

Programs will differ slightly on this.

I tend to be on the higher side of recommendations and would recommend at least 64 ounces of hydrating fluids but even better to get towards 96 ounces.

The Academy of Nutrition and Dietetics Pocket Guide to Bariatric Surgery recommends 48 to 64 ounces.

Another way to calculate fluid needs is to drink one ounce per kilogram of body weight. For those of us who use pounds for body weight, we divide our weight by 2.2 to get kilograms.

This means 64 ounces of water is technically for someone who weighs 140 pounds. Considering less than 5% of bariatric surgery patients lose to a BMI of 25 or less, it is safe to say 64 ounces is not the right number for most!

While that might be an overwhelming number (one ounce per kilogram) I use it to illustrate that most of us feel better at a higher intake of water. Though if you really struggle with water and you’re doing your best to get 48 ounces, the AND does state this will help most avoid the need for IV fluids.

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Symptoms of dehydration

If you are not getting at least 48 ounces of water a day and have any symptoms of dehydration, call your surgery center today. 

flushed face
extreme thirst
dark urine
dizzy or weak
cramping in arms and legs
sleepy or irritable feeling
dry mouth, dry tongue

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What counts as water after bariatric surgery

Again, programs will differ slightly but traditionally hydrating fluids consist of any liquid that is:

not caffeinated
not carbonated
less than 15 calories per 8 ounces (not sugar containing)

Below is a list of fluids that can count as water (there are more than on the list!)

Flavored Water
Gatorade or Powerade Zero
Diet Snapple
Diet Lipton Green Tea
Crystal Light
Sugar-free Kool-aid
Ocean Spray Diet Cranberry
Smart Water
SOBE LifeWater Zero
Decaf coffee (unless loaded with creamer!)
Decaf tea
Sugar-free lemonade
True Lemon or True Lime packets
Chicken, beef or vegetable broth
Sugar free popsicles or jello

Need recipe ideas for the liquid phase diet after bariatric surgery? This blog has 26 of them! 


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Other tips to drink enough water after Gastric Sleeve or Bypass

As simple as it may seem, there are small tweaks that can make a big difference to get more fluid in your day.

Many patients over the years have explain to me their water MUST be cold. Another patient will tell me it has to be room temperature since surgery. Another will tell me they notice getting in a lot more when it’s warm like herbal tea. Try different temperatures and notice if it makes a difference for you!

Water bottle:
Ask around what water bottle people prefer. It may seem silly but we tend to gravitate to a certain water bottle that fits us best. You might want it to be large to help you count down how many ounces you need.

Or instead you may prefer something smaller and less intimidating. You might want an insulated bottle to keep it really cold (see temperature above) or something that fits in your cupholder. Write down things like this before you start shopping for a bottle. Having a favorite water bottle is SO helpful to drinking more!

Lid off:
If you have a bottle with a removable lid or straw, many patients report needing to keep the lid off especially if they are sitting at a desk. Water could be sitting next to them all morning, untouched with the lid on. Compare this to something with a straw or lid that pops up and you may be more likely to lift and drink.

Straws are okay: 
There are some misnomers about bariatric surgery that have changed through the years. Straws have not been shown to be a significant issue after surgery. Certainly take note if drinking through a straw causes any discomfort, gas, bloating or belching. For many patients, however, they find it helps them drink more water when they have a straw!

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Situations that require you to drink even more water

There are times when our body needs even more water! Our water needs will go up in these conditions:

✔️ exposure to extreme temperature (hot or cold) as the body works to maintain normal temperature
✔️ strenuous work or exercise
✔️ airplane travel (or other instances of recirculated air)
✔️ during pregnancy and breastfeeding (here is a blog series on that topic!)
✔️ during sickness (fever, diarrhea, vomiting)

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