Reactive Hypoglycemia After RNY

Reactive Hypoglycemia After RNY: Causes, Signs, and Treatments

February 9, 2018

Following gastric bypass surgery, some patients report experiencing the condition reactive hypoglycemia.  The name, reactive hypoglycemia, defines what is happening.

Why Reactive Hypoglycemia After RNY Occurs?

Reactive indicates that the body is reacting or responding to a change, and this reaction is typically caused by eating sugar or simple carbohydrates.

Hypoglycemia means that the body’s blood sugar drops too low, causing the patient to experience symptoms of low blood sugar. These symptoms range from jittery shakes, numbness, and/or dizziness to fatigue, foggy thinking, heart palpitations and even loss of consciousness. It is, in the simplest of terms, a sugar crash.¹

So we ask: Why is reactive hypoglycemia more common following gastric bypass?  It is more common because of the changes and the responses that follow the bypass operation.  Let’s better understand what has changed.

The Stomach

The first change:  The average capacity of our normal stomach is 1,000 – 1250 cc's – about the size of a football.  After gastric bypass, the new stomach’s capacity is 15-30 cc's, or about 2% the size of the previous normal stomach.

The second change:  Our normal stomach has an outlet “valve” termed the pylorus which functions to slowly release ingested food, liquids, and sugars from the stomach into the digestive system.  Following gastric bypass, the new stomach (pouch) does not have an outlet valve but is always open.  This opening is small, 1.2 – 1.5 cm in size, allowing liquids and sugars to flow through easily while slowing the transit of food.  That’s why it is important, after gastric bypass, to chew one's food or crush one's pills so either solids or medication can pass easily through this fixed small opening.

Small Intestine and Sugar

The third change:  After gastric bypass, the small open stomach is rerouted to directly connect to the small intestine instead of traveling through a digestive channel called the duodenum. The function of our small intestine is absorption.  After gastric bypass when one consumes sugar, the sugar passes quickly through the open small stomach into the small intestine and is absorbed, without delay, by their small intestine.  This results in a rapid rise in their blood sugar.

The Pancreas

The pancreas is located just below the stomach.  It has numerous digestion functions including the regulation of our body’s blood sugar. When blood sugars rise, the pancreas responds by releasing the hormone insulin.  Insulin stimulates the tissues and cells to absorb excess sugar, bringing blood sugar back down into a normal range.  This regulation is what fails in the disease of diabetes.  In Type 1 diabetes, the pancreas is not capable of releasing insulin anymore.  In Type 2 diabetes, the body is not responding to the insulin released.  This is why diabetes is a condition of abnormally and consistently high blood sugars.

The Brain

The brain’s fuel source is sugar.  Sugar, (glucose), is what drives all of our brain functions.  Our brain is unable to use fats, proteins or other fuels for energy, which is different from other organs and tissues of our body.  When blood sugars drop too low, our brain runs out of fuel, much like a car running out of gas.  Brain starvation is what causes the symptoms of hypoglycemia including jittery shakes, numbness, dizziness, fatigue, foggy thinking, heart palpitations and even loss of consciousness.

The Problem is Not What Has Changed, but What Has Not

What has not changed is that our pancreas and its release of insulin is programmed to react to our normal stomach.  I repeat, our pancreas and its release of insulin are programmed to react to our normal stomach – to the original size stomach with its slow release valve (the pylorus), and the normal digestive channel that follows prior to entering our small intestine.

Normally sugar, when consumed, will be delayed every step of the way.  However, after gastric bypass, when sugar is consumed, this sugar passes quickly through the small open stomach, entering directly into the small intestine, absorbed immediately by such, resulting in a rapid rise in ones’ blood sugar.  Their pancreas responds to this rapid rise by releasing insulin. Because of the pancreas’s programming, it is expecting more sugar to follow over a much longer period of time.  The pancreas reaction is that too much insulin is released for too long.  This too much insulin signals ones’ body to absorb, and absorb, and absorb, all of their blood sugar, resulting in a sugar crash because there is no fuel left for their brainViola!!! Reactive Hypoglycemia.

Bring on the Candy Bar…A True and Somewhat Scary Story

When my RNY patient, decided to eat a candy bar this, is what followed.  She is a compliant patient, so I am sure that she chewed that candy bar to applesauce consistency.  She ate that candy bar quickly because she wanted a quick snack before she started driving her work vehicle.  The candy bar, being mostly sugar and well chewed, liquefied quickly, easily flowing through her always open stomach into her small intestine.  Her small intestine absorbed the sugar immediately, causing a rapid rise in her blood sugars.  Her pancreas responded by releasing insulin.   Of course, the programmed pancreas released too much insulin and for too long.  She absorbed all of her blood sugar, again and again, leaving no fuel for her brain (hypoglycemia). Her brain is starved. A sugar crash followed.  She became symptomatic.  Her symptoms were severe.  She passed out (reaction).  Unfortunately, she was driving at the time. What? Thank goodness she was okay and no one was hurt.

This is an extreme example of reactive hypoglycemia. More often, patients will have symptoms of low blood sugar which range from shakiness, and fatigue to palpitations, depending on how low their blood sugars fall.  It can be as subtle as just feeling like they need a nap.

How do you avoid reactive hypoglycemia?  The best advice is to eat three to four protein-forward, balanced meals daily - spaced three to four hours apart.  Ultimately, almost every patient finds their own balance and their food choices and timing that work best for them.

What Happens if You Do Experience Reactive Hypoglycemia?

The good news is that it will pass.  You may feel terrible, but once your blood sugar normalizes, you feel better.  In the short term, your symptoms might be reduced by drinking a small amount of juice or introducing another simple sugar (sugar tab), and in most cases, the symptoms will pass quickly.  A lesson well learned by many but one that has a lasting impact on what not to do in the future.

Do patients think this is a good thing?  Some have.  The answer is: Hopefully not.  Let me clarify.  I have been with practices throughout my career that understand and stress the importance of diet, exercise and making good food choices following gastric bypass surgery.

This education includes the importance of choosing quality nutritious foods that provide the most bang for your buck. With education, patients can be more mindful, choosing foods that will provide good nutrition, maximize fullness while limiting adverse reactions.  Protein-forward meals, coupled with complex carbohydrates, do just that - providing fullness, slower transit, a slower breakdown in the digestive system, avoiding a rapid rise in blood sugar and limiting problems like reactive hypoglycemia.

Still Experiencing Reactive Hypoglycemia Symptoms?

That said, if you find yourself following this advice, paying attention to your education, eating adequate protein balanced meals while limiting sugar and simple carbohydrate consumption but still are experiencing reactive hypoglycemia symptoms, then you need to contact your physician or bariatric surgeon. Why?  Because there are other less common, causes of reactive hypoglycemia.   Some examples include stomal dilatation, exogenous insulin exposure, insulinoma disease.

For patients that are trying to decide if the benefits of the Roux en Y gastric bypass outweigh the risks such as reactive hypoglycemia, my advice, is unequivocally yes! Mindful eating and using the tools that you will be given will guide you through this weight loss journey. No doubt it will be a lot of work and effort on your part but the reason you are having weight loss surgery is to become a healthier person.  Making healthy choices is the key to that success, and in so doing, you can keep reactive hypoglycemia at bay.


  1. The Wikipedia definition is as follows:  reactive hypoglycemia is a medical term describing recurrent episodes of symptomatic hypoglycemia occurring within 4 hours[1] after a high carbohydrate meal in people who do not have diabetes.[2] It is thought to represent a consequence of excessive insulin release triggered by the carbohydrate meal but continuing past the digestion and disposal of the glucose derived from the meal.
Jeffrey Baker


Dr. Jeffrey Baker is a board-certified physician specializing in bariatric surgery. He has performed over 2,500 weight loss surgeries since specializing in bariatrics in 2003. He sits on the review boards of two international state-of-the-art medical device companies developing new technologies for bariatric innovations.

Read more articles by Dr. Baker!