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Gastric Bypass Surgery Can Lead to Low Blood Sugar

Gastric Bypass Surgery Can Lead to Low Blood Sugar

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      Gastric bypass surgery can help many people lose weight and lower their risk of diabetes (1). Not to mention, that it can help those with diabetes wean off their medications. However, in some people, gastric bypass surgery can cause episodes of low blood sugar (2). These episodes can be dangerous if left untreated.

      In patients that experience episodes of low blood sugar regularly after gastric bypass, some treatment options may help. For example, certain diet modifications and medicines may help reduce gastric bypass blood sugar episodes. Read on to learn more about gastric bypass surgery, how it can impact blood sugar levels after surgery and treatment options.

      Fast facts about gastric bypass surgery

      Also known as Roux-en-Y, gastric bypass surgery is a weight loss surgery that can reduce the size of the stomach (1). In addition, the surgery connects the smaller stomach pouch to the middle half of the small intestine.

      Gastric bypass surgery can produce significant weight loss (3). This weight loss can be successful at lowering the risk of obesity-related conditions like heart disease, diabetes, and breathing issues like sleep apnea (1,3).

      How can gastric bypass surgery help blood sugar levels and diabetes?

      Experts report that gastric bypass surgery can be an effective weapon against type 2 diabetes. One may suspect that this is due to the significant weight loss that the surgery produces. However, it’s also due to the metabolic changes that occur after surgery like (4):

      • effects on tissue-specific insulin sensitivity
      • changes in beta-cell function
      • changes in bile acid composition and flow
      • modifications of gut microbiota
      • changes in intestinal glucose metabolism
      • increased brown adipose tissue metabolic activity

      According to the American Society for Metabolic and Bariatric Surgery (ASMBS), bariatric surgery improves type 2 diabetes in 90-percent of patients, specifically for gastric bypass, around 80% of patients go into remission(5). It helps improve symptoms, reduce the need for diabetes medications, and lowers blood sugar.

      Gastric bypass and low blood sugar

      Beer being poured into a glass.
      Alcohol should be avoided after gastric bypass surgery to lower risk of hypoglycemia.

      It’s important to note that along with the treatment of diabetes through gastric bypass surgery, comes the risk for low blood sugar - hypoglycemia (2). Researchers suggest that this is likely due to the lack of improvement of beta-cell sensitivity to blood glucose levels after gastric bypass surgery (6). In turn, the body responds with inappropriately high insulin secretions that can lead to hypoglycemia.

      Some experts also suggest that after gastric bypass surgery, the rapid passage of nutrients in the body causes a rapid rise in blood glucose levels (7). This leads to high post-meal insulin levels that can cause hypoglycemia. This may be due to the phenomenon known as dumping syndrome in which your food or the sugar from the food you eat empties into the small intestine faster than usual (8).

      This type of hypoglycemia is also known as reactive hypoglycemia. It can occur in patients a year or more out of gastric bypass surgery (9). Symptoms of low blood sugar of this kind include:

      • shakiness
      • hunger
      • dizziness
      • cold sweats
      • confusion
      • anxiety
      • possible loss of consciousness

      You can treat these symptoms by consuming a carbohydrate-rich food or drink. However, it’s important to know that hypoglycemia after gastric bypass surgery can be life-threatening. This is because it can lead to seizures, altered consciousness, or accidents (10).

      How can I treat gastric bypass low blood sugar?

      Hourglass with red sand running through it.
      It’s important to take time to chew food well for at least 30 to 60 minutes to lower risk of low blood sugar levels.

      Although some cases of low blood glucose after gastric bypass may require medication, you can prevent many episodes with diet changes (7). Besides eating frequent small meals throughout the day, you can avoid low blood sugar by also (9,11):

      • eating a small carbohydrate choice equaling about 5 grams of carbohydrate with a small serving of protein when you first start to feel any weakness or dizziness that could be related to low blood sugar levels
      • consuming glucose tablets if you experience more severe hypoglycemic symptoms
      • avoiding sugary foods that can trigger the release of insulin
      • not consuming alcohol since it can prevent blood sugar regulation in the liver and contribute to low blood sugar

      For your overall diet regimen after gastric bypass surgery, you should focus on specific foods to prevent low blood glucose. This means eating mostly whole, unprocessed foods like lean proteins, high-fiber fruits and vegetables, and unrefined whole grains. It would help if you were eating such foods every 3 to 4 hours to prevent low blood glucose levels.

      Salad on a plate.
      Make sure to balance protein and carbs at mealtime to reduce risk of hypoglycemia.

      Other ways you can prevent low blood sugar levels

      Woman drinking water from a glass.
      It’s important to avoid drinking fluids while eating after gastric bypass surgery to lower risk of low blood glucose levels.

      Besides those diet changes listed above, you can also follow the guidelines below to prevent hypoglycemic episodes (11,12).

      • Eat protein sources at each meal and snack time like beef, chicken, turkey, tuna, seafood, nuts, seeds, or dairy products like milk, yogurt, or cheese.
      • Avoid skipping meals and snacks, which can lead to low blood sugar. Also, skipping meals can cause you to eat more concentrated sources of carbohydrates at the next mealtime. This, in turn, can increase levels of insulin secretion.
      • Avoid or limit caffeine since it can rapidly increase blood glucose via reduced glucose uptake into skeletal muscle.
      • Include heart-healthy fats in each meal and snack since they do not trigger insulin secretion. Such foods include nuts, nut butter, avocado, olives, plant-based oils like olive and sunflower oil, most seeds, and oily fish like salmon, tuna, and sardines.
      • Chew food more thoroughly. Not only can chewing your food more per bite (about 20 to 25 times per bite) help keep you from overeating at once. However, it can also help prevent low blood glucose levels by preventing food from emptying too fast into your stomach.
      • Avoid liquids while eating. It’s important not to drink liquids too much while eating after gastric bypass surgery. This is because drinking liquids while eating can make food release flow faster to the intestine. This can lead to increased glucose absorption and insulin secretion. Therefore, try to eat each meal or snack slowly over 30 to 60 minutes and separate eating from drinking by at least 30 minutes.

      It’s also important that if you experience low blood glucose symptoms after gastric bypass surgery, that you start checking your blood sugar levels. You can receive more information on this from your healthcare provider.

      Take home message

      Person taking blood from their finger.
      If you experience low blood sugar symptoms often after gastric bypass surgery, it may be time to start checking your blood glucose levels at home.

      Gastric bypass surgery can be life-changing surgery for those who need to lose weight or have diabetes. However, like with any surgery, there can be risks. One such risk after gastric bypass surgery is low blood sugar. Although it may seem harmless, low blood sugar can be dangerous to your health if left untreated.

      That’s why it’s important to see your doctor right away if you experience any low blood sugar symptoms after surgery. Then, if you receive a diagnosis of low blood sugar, a low carbohydrate diet regimen or medicine could help reduce or resolve your low blood sugar episodes.In severe cases of hypoglycemia, you may need to consult endocrinology for more intense medical treatment or, in extreme cases, when symptoms are impossible to control - surgical reversal might be an option. Please consult your health care provider to find out if this could be a consideration for you.


      1.       Mayo Clinic (December 28, 2017) “Gastric bypass (Roux-en-Y).”

      2.       Mayo Clinic (September 7, 2018) “Hypoglycemia.”

      3.       UCLA Health (accessed August 29, 2019) “Gastric Bypass Surgery.”

      4.       Koliaki, C., Liatis, S., le Roux, C.W., and Kokkinos, A. (August 2017) “The role of bariatric surgery to treat diabetes: current challenges and perspectives.” BMC Endocr Disord., 17(1):50.

      5.       American Society for Metabolic and Bariatric Surgery (accessed August 29, 2019) “Surgery for Diabetes.”

      6.       Capristo, E., et al. (June 2018) “Incidence of Hypoglycemia After Gastric Bypass vs Sleeve Gastrectomy: A Randomized Trial.” The Journal of clinical endocrinology and metabolism, 103(6): 2136-2146.

      7.       Kirby, J.L. and O’Donnell, K. (June 2016) “Hyperinsulinemic Hypoglycemia After Gastric Bypass Surgery.” Practical Gastroenterology, pgs. 22-27.

      8.       Cleveland Clinic (accessed August 29, 2019) “Dumping Syndrome.”

      9.       Ridgeview Medical Center (accessed August 28, 2019) “Reactive hypoglycemia post-gastric bypass.”

      10.   Goldfine, A.B. and Patti, M.E. (June 2016) “How common is hypoglycemia after gastric bypass?” Obesity (Silver Spring), 24(6):1210-1.

      11.   St. Joseph’s Healthcare Hamilton (accessed August 28, 2019) “Reactive Hypoglycemia After Bariatric Surgery.”

      12.   Suhl, E., Anderson-Haynes, S.E., Mulla, C., and Patti, M.E. May 2017) “Medical nutrition therapy for post-bariatric hypoglycemia: practical insights.” Surg Obes Relat Dis., 13(5):888-896.

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        Staci Gulbin, MS, MEd, RD


        Staci has been a registered dietitian with the Commission on Dietetic Registration since 2010 and has over a decade of experience in the nutrition and dietetics industry.

        Gintas Antanavicius, MD, FACS, FASMBS

        Medical Reviewer

        Dr. G is a co-founder of BariBuilder. A US-based expert surgeon with over 10 years of bariatric experience, he regularly publishes research in medical journals like SOARD, Obesity Surgery, etc.