What Is Reactive Hypoglycemia?

Reactive hypoglycemia, also called postprandial hypoglycemia, is a drop in blood glucose (blood sugar) levels. This typically happens within four hours after eating and is not related to diabetes.

Usually, a definitive cause of reactive hypoglycemia cannot be determined, although there are a handful of medical diseases and conditions known to be associated with it. In those cases, treating the underlying issue will put an end to post-meal low blood sugar.

Otherwise, managing reactive hypoglycemia starts with recognizing the symptoms, which can range from mild (shaking, rapid heart rate, anxiety, hunger) to serious (confusion, vision difficulties, behavioral changes, seizures, or even loss of consciousness).

Symptoms

Reactive hypoglycemia can cause symptoms that range from common ones that are mild and unsettling to less frequent symptoms that can become serious and even life-threatening if the condition isn't treated.

Common Symptoms

• Shaking or tremors
• Hunger
• Rapid heartbeat
• Anxiety or panic
• Tingling near the mouth
• Sweating
• A headache
• Fatigue
• Inability to concentrate
• Dilated pupils
• Irritability
• Restlessness
• Nausea
• Dizziness
• Weakness
• Loss of muscle control

Severe Symptoms

• Confusion
• Changes in behavior
• Slurred speech
• Clumsy movements
• Blurry or double vision
• Seizures
• Loss of consciousness

Diagnosis

Reactive hypoglycemia can be diagnosed by measuring the amount of glucose in a person's blood while they're having symptoms that develop after eating as well as by observing whether or not those symptoms resolve once glucose levels return to normal.

If testing reveals a postprandial blood glucose level below 70 milligrams per deciliter (mg/dL), a doctor may order a mixed meal tolerance test (MMTT). For this test, a person downs a beverage that contains protein, carbohydrates, and fat such as Ensure or Boost.

Before ingesting the beverage and every 30 minutes for five hours, his or her blood will be tested to check levels of glucose as well as insulin, proinsulin (a precursor to insulin), and a substance produced in the pancreas along with insulin.

Causes

For the majority of people who experience reactive hypoglycemia, there's no apparent or diagnosable reason for the characteristic blood sugar dips. However, there are a few known potential causes:

• Insulinoma, a rare, usually benign tumor made up of abnormal beta cells—the cells that produce insulin needed to maintain normal blood sugar
• Excessive intake of insulin by someone who has diabetes
• Gastric bypass surgery, which may cause food to pass so quickly through the digestive system that not all of it is digested and therefore is absorbed as glucose into the bloodstream
• Hernia surgery
• Certain inherited metabolic disorders—specifically known as endogenous hyperinsulinism linked to non-insulinoma pancreatogenic hypoglycemia syndrome (NIPHS) or very rarely, inherited fructose intolerance
• Enzyme deficiencies that interfere with the body's ability to break down food

Treatment

If it's determined that an underlying medical issue is causing reactive hypoglycemia, treating that disease or condition should put an end to post-meal dips in blood glucose. In the case of an insulinoma, surgical removal of the tumor should put an end to post-meal hypoglycemia.

For all other cases, there are two distinct aspects of treating reactive hypoglycemia. The first is knowing what to do to alleviate symptoms when they occur. The second is making lifestyle changes and taking other steps to prevent blood sugar drops after meals to occur in the first place.

Dealing With an Episode

The symptoms of reactive hypoglycemia can be mitigated by taking certain steps to return blood glucose levels to normal:

First, follow the "15-15 Rule," which involves eating 15 grams of fast-acting carbohydrates and checking your blood sugar after 15 minutes. If it’s still below 70 mg/dL, have another serving.

Once your symptoms have resolved, eat a small snack or meal to prevent your blood sugar from spiking and dropping again. Some good options are:

• Glucose tablets (see instructions)
• Gel tube (see instructions)
• 4 ounces (1/2 cup) of juice or regular soda (not diet)
• 1 tablespoon of sugar, honey, or corn syrup
• Hard candies, jellybeans, or gumdrops—see food label for how many to consume

Prevention

The cause of most cases of reactive postprandial hypoglycemia cannot be determined. Even so, certain dietary and lifestyle changes are known to help prevent it:

• Limit foods that have a high glycemic index, such as sugary ones and processed simple carbs like white bread and pasta—especially on an empty stomach. For example, eating a doughnut first thing in the morning can trigger a hypoglycemic episode.
• Eat small, frequent meals and snacks that include fiber and protein. Don't go longer than three hours without eating.
• If you drink alcohol, always eat while you imbibe. Don't use sugary soft drinks as mixers.
• Eat a balanced and varied diet that includes protein, whole-grain carbs, vegetables, fruits, dairy foods, and lots of fiber.
• Exercise regularly: Physical activity increases the amount of glucose taken up by the blood which in turn prevents the release of excessive insulin.

A Word From Verywell

If you experience the symptoms of low blood sugar levels after you eat, see your doctor. Some symptoms can be similar to those of other conditions, such as heart disease, so you'll want to be certain a potentially serious medical problem isn't responsible for your post-meal dips in glucose. Once it's clear you're experiencing reactive hypoglycemia, even if your doctor can't find a specific reason it should be a relief to know that there are simple measures you can take to handle, and prevent, episodes from occurring.