What to Know About Reactive Hypoglycemia

Medically Reviewed By Mia Armstrong, MD
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Low blood sugar levels about 4 hours after eating a meal is a sign of reactive hypoglycemia. The symptoms may include shakiness, sweating, and fatigue. This condition may require diet and lifestyle changes, as well as continuous glucose monitoring (CGM). Reactive hypoglycemia is not the same as hypoglycemia, which is low blood sugar (glucose) that can occur when you are not eating enough or intentionally fasting.

The exact cause of reactive hypoglycemia is not known, but it may be due to excess insulin production or due to how the body responds to insulin. Insulin is a hormone that allows glucose from the bloodstream to enter cells. Your cells use the glucose for energy.

Having more insulin than your body needs could cause a dangerously low drop in blood glucose. According to the Endocrine Society, this can happen in people with diabetes who must take insulin or other medications to lower their blood glucose level.

The Endocrine Society says that non-diabetic hypoglycemia, including reactive hypoglycemia, is rare.

Treating reactive hypoglycemia may involve a combination of dietary changes and medications.

This article will explain regular changes in blood glucose and what happens with reactive hypoglycemia. You will learn about the signs of reactive hypoglycemia, possible causes, and what may help if you have reactive hypoglycemia.

Understanding hypoglycemia and reactive hypoglycemia

man in hot growing house with hand on head indicating fatigue
Milles Studio/Stocksy United

Hypoglycemia is the general term to describe blood glucose levels below the normal range. It is a blood glucose value of less than 70 milligrams per deciliter (mg/dl), according to the American Diabetes Association (ADA). The reason why hypoglycemia is rare in people not taking insulin for blood glucose management is because the body has an intricate way of regulating blood glucose.

Blood glucose regulation

Your blood sugar level is constantly changing throughout the day as your body expends energy and adapts to regular activities. People do not usually notice typical fluctuations in blood glucose.

After you eat, your body breaks down food into simpler substances, including glucose, that it can use for energy. This increases the amount of glucose in the blood.

When glucose levels rise, your pancreas releases insulin. This drives glucose into your cells and blood glucose levels decrease. When blood glucose reaches a threshold level, the pancreas releases the hormone glucagon. This makes the liver release stored glucose into the bloodstream, which raises blood glucose.

This cycle of insulin and glucagon maintains regular blood glucose concentrations.

Learn more about glucose here.

Different categories of hypoglycemia include diabetic, fasting, and reactive.

Diabetic hypoglycemia

Many people know that diabetes is a condition in which blood glucose reaches high levels — called hyperglycemia. To prevent this, people with diabetes need to take insulin or other medications. There are three types of diabetes:

  • Type 1 diabetes is when your pancreas does not make insulin or does not make enough of it. People with this type must take insulin.
  • Type 2 diabetes is when you do not make enough insulin or it is not used effectively. People with this type may need to take insulin.
  • Gestational diabetes is diabetes during pregnancy. Insulin injections may be necessary to manage glucose levels.

Under some circumstances, these treatments can decrease blood glucose too much, resulting in hypoglycemia. According to the ADA, low blood sugar levels are common for people with type 1 diabetes but can also affect patients with type 2 diabetes who are taking insulin or medications. When this happens, the person needs to eat something or take glucose tablets to raise their blood glucose quickly. If this happens regularly, the person may need to adjust their treatment.

People with diabetes monitor their blood glucose levels at regular intervals as a way of maintaining glucose in the normal range or one agreed upon with their physician.

Learn how insulin helps people with diabetes here.

Fasting hypoglycemia

Fasting hypoglycemia usually only happens if you do not eat when you need to or you intentionally skip a meal. Other causes include certain medications, illnesses, and low levels of certain hormones.

Reactive hypoglycemia

If you have reactive hypoglycemia, the amount of glucose in your blood gets dangerously low several hours after a meal. This typically occurs within 2–5 hours after eating. Another term for it is postprandial hypoglycemia. Without treatment, your body will not have enough energy to function.

What are the symptoms of reactive hypoglycemia?

Common physical symptoms of reactive hypoglycemia include

Extremely low glucose levels in the brain may cause additional signs and symptoms, such as:  

Seek medical attention right away (call 911) for seizures, loss of consciousness, or other worsening symptoms.

What causes reactive hypoglycemia?

A 2019 review article suggests reactive hypoglycemia can possibly derive from an excess of insulin production or an increase in the body’s response to insulin after food consumption. Insulin causes the glucose to enter cells, resulting in hypoglycemia, which means there is less circulating glucose in the bloodstream. However, the exact cause of reactive hypoglycemia for most people is not clear. This is called idiopathic reactive hypoglycemia.

Factors that can increase the chance of developing reactive hypoglycemia include: 

How do you diagnose reactive hypoglycemia?

If you have symptoms of reactive hypoglycemia, your doctor will perform a medical evaluation and order lab tests to determine whether low blood sugar is the direct cause of your symptoms and whether raising your blood sugar resolves symptoms.

The diagnostic workup for postprandial hypoglycemia may involve a prolonged oral glucose tolerance test (OGTT) or mixed meal tolerance test (MMTT). These tests measure the amount of glucose in a sample of your blood after you fast and then after you consume liquid or solid glucose, respectively. Fasting mean nothing to eat or drink except for water for at least 8 hours.

The OGTT is one of several methods doctors use to diagnose diabetes and prediabetes, a condition in which your blood glucose levels are higher than normal but not as high as in diabetes. Another test is the fasting plasma glucose (FPG) test, which measures the level of glucose in the plasma portion of your blood at a single point in time after you fast for at least 8 hours.

Your doctor may evaluate you for prediabetes and diabetes alongside testing for reactive hypoglycemia. This is because reactive hypoglycemia can be associated with prediabetes.

The following diagnostic values for prediabetes and diabetes are from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). All glucose values are in mg/dl except where noted.

DiagnosisA1CFasting plasma (blood) glucoseOGTTRandom plasma glucose test
Normalbelow 5.7%99 or below139 or below
Prediabetes5.7–6.4%100 to 125140 to 199
Diabetes6.5% or above126 or above200 or above200 or above

Learn about diabetes and A1C test results here.

Oral glucose tolerance test for reactive hypoglycemia

The OGTT to aid in a prediabetes or diabetes diagnosis has these steps:

  • Fast for at least 8 hours.
  • Get a blood draw from a vein in your arm.
  • Drink a liquid containing 75 grams of glucose.
  • Get a blood draw at 1-hour intervals for 2–3 hours.

To evaluate reactive hypoglycemia, your doctor may continue the test for 5 hours.

You may be diagnosed with reactive hypoglycemia if your blood glucose is less than 60 mg/dl 4–5 hours after glucose consumption, according to a 2019 article. However, the article states that OGTT can generate false positive results and may not be an accurate way to diagnose or exclude a diagnosis of reactive hypoglycemia.

Mixed meal tolerance test

The MMTT is like the OGTT except you consume a solid meal of specific amounts of protein, carbohydrates, and fat. The meal represents what you might consume in a typical meal.

A blood glucose value of less than 60 mg/dl 4–5 hours after glucose consumption is a sign of reactive hypoglycemia, but it is not required for a diagnosis. A 2021 study shows that the MMTT may produce a false negative result in people with suspected reactive hypoglycemia. This is because blood glucose levels did not fall below the threshold level, even though the people in the study were experiencing symptoms of hypoglycemia.

The doctor may also want to monitor your glucose levels over a few days to confirm whether symptoms disappear after your blood sugar returns to normal levels. Maintaining a consistent eating schedule and food diary can help identify specific symptoms before and after every meal.

What are some ways to treat and prevent reactive hypoglycemia? 

Reactive hypoglycemia does not require a specific clinical treatment. Depending on symptoms and medical history, your doctor can recommend dietary and lifestyle changes for prevention.

Diet 

The following dietary recommendations may help improve symptoms: 

  • Include high fiber foods and whole grains in your diet.
  • Limit alcohol consumption, or do so in small amounts with a meal.
  • Limit your intake of foods and beverages with refined sugar on an empty stomach. 
  • Plan ahead to eat small meals throughout your day, as this can keep your blood sugar stable.
  • Limit your caffeine consumption to 1 cup per day and check labels, as tea and sodas may contain caffeine.

You may also work with a registered dietitian to learn more about how to make nutritional choices.

Lifestyle 

According to the Centers for Disease Control and Prevention (CDC), at least 20–25 minutes of daily physical activity can help control blood sugar levels and may lower your risk of heart disease, lower your risk of chronic conditions, and improve mental health. Start with 10 minutes per day until you increase and reach 150 minutes per week. 

A few suggestions to incorporate physical activity include: 

  • riding a bicycle 
  • attending dancing classes
  • doing yoga and Pilates 
  • walking around your neighborhood 
  • gardening or mowing the lawn

It is important to be aware of your mental health too, since stress levels can affect your overall well-being. Find activities that promote wellness, such as walking outside, breathing exercises, and creative hobbies. 

Medication 

According to this 2019 article, some people with reactive hypoglycemia can benefit from taking metformin, an antidiabetic drug. If your symptoms are due to prediabetes, your doctor may recommend this medication. 

If you are experiencing a sudden episode of hypoglycemia, an intake of 15 grams of carbohydrates can stabilize your blood sugar levels. You can eat candy, glucose tablets, or drink juice. Symptoms should improve after 20 minutes.

Learn more about glucose tables and when to take them here.

What is the outlook? 

Although reactive hypoglycemia does not represent a prediabetes or diabetes diagnosis, pay attention to your symptoms and follow your doctor’s recommendations.

Medications, preexisting conditions, diet, and stress can affect blood sugar levels. As such, it is a good idea to keep track of significant changes in your health and life events and how they may affect your symptoms. Wearing a glucose meter can be helpful when managing symptoms of reactive hypoglycemia. 

Maintaining a moderate weight can help prevent irregular glucose levels and other health conditions.

Learn how pain relievers can affect blood sugar levels here.

Summary

Reactive hypoglycemia is a type of hypoglycemia that occurs when you experience low blood sugar levels 2–5 hours after eating a meal. People who are overweight, have had gastric surgery, or have a metabolic disease may be prone to the condition.

Keeping a balanced diet, eating small but frequent meals throughout the day, limiting alcohol consumption, and incorporating physical activity can help improve symptoms.

If necessary, your doctor can create a specific prevention plan and recommend medication to help manage your blood glucose levels.

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Medical Reviewer: Mia Armstrong, MD
Last Review Date: 2022 Jun 6
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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