Hypoglycemia occurs when blood glucose levels dip below normal ranges (i.e., less than 50 milligrams of glucose per deciliter of blood, or mg/dL).^[1][2] Reactive hypoglycemia (RH) is a subtype of hypoglycemia which is often defined by a dip in blood glucose that occurs 2–5 hours after a meal (postprandial). Since RH is not fully understood, its definition varies and sometimes also includes a dysfunctional response to insulin and/or to the consumption of specific foods. RH may occur in both individuals with and without diabetes and may lead to insulin resistance.^{[3][4][5] [6][7][8][9][10]} RH has been categorized into at least three forms, which depend on how quickly symptoms appear after eating: RH that occurs 2–3 hours post meal is considered alimentary, 3–4 hours after a meal is idiopathic, and longer than 4 hours post meal is called late RH.^[6][7]

RH shares characteristic symptoms with mild hypoglycemia (low blood sugar), which stem from the activation of the autonomic nervous system and may include the following symptoms: heart palpitations, pale skin, tremors, high blood pressure, anxiety, perspiration, hunger, nausea, and/or the sensation of “pins and needles”.^[9][2]

As blood glucose levels dip below the concentrations needed to power vital organs (50 mg/dL), vision disturbances, cognitive changes, mood changes, lightheadedness, fatigue, headache, and seizures may occur.^[10][6][2]

Diagnosis and definition of RH can be difficult since it requires first ruling out other conditions (e.g., diabetes, hormonal dysregulation, peptic ulcer disease, alcoholism).^[11][5][12] Currently, there are no standardized biochemical tests or procedures that can definitively diagnose RH.^[11][8][9]

The timing and presentation of hypoglycemia relative to meals is a key feature of RH, so a comprehensive symptom and medical history are requisite steps in diagnosis.^[11][6][5] Blood glucose assessment helps to confirm hypoglycemia, though there is still some debate as to which test is most suitable for the diagnosis of RH.^[11][5] While the presence of hypoglycemia may be established by tests such as continuous glucose monitoring, mixed-meal tolerance tests, oral glucose tolerance tests, and ambulatory glucose testing,^{[5][12][13][9][2]} no specific level of blood glucose has been established as a cutoff for the diagnosis of RH.^[11][8][9]

When RH occurs as a result of an identifiable underlying medical condition, treating that condition is the first line of care.^[1]

Otherwise, although there are currently no dietary guidelines in place for RH management, lifestyle, and dietary modifications may reduce the severity of symptoms.^[8] Dietary changes may include balancing meal composition (combining complex carbohydrates, proteins, and fats), eating more frequently, reducing meal sizes, avoiding trigger foods (simple sugars and processed carbohydrates), and increasing fiber consumption.^[7][8][3][9] Lifestyle modifications, such as regular exercise, may also be recommended when appropriate.^[1]

Currently, no supplements are known to be studied for RH specifically, but supplements that are effective for another, possibly overlapping condition known as dumping syndrome may also be effective for RH (see Other FAQs for further clarification).^[12][14] Supplements have also been studied for more general blood glucose regulation, but these have not been specifically studied for RH.

Regarding dumping syndrome, one systematic review found that bulking/thickening supplements, such as guar gum, pectin, and glucomannan, could reduce symptoms by slowing gastric emptying. However, these supplements can be poorly tolerated, due to side effects like gas and bloating.^[12] Traditional Chinese herbs have also been explored for symptomatic improvement, but more studies of higher quality are required before any conclusions can be drawn regarding their efficacy and safety.^[14]

Diet plays a critical role in RH, as the types and timing of food consumption impact blood sugar levels. Evidence suggests that avoiding meals high in simple carbohydrates, refined sugars, and alcohol consumption may reduce RH symptoms. ^[15][11][9] Meal composition, balance, frequency, timing, and portion size are some of the most commonly cited methods of controlling blood sugar fluctuations.^[8] Evidence also suggests that diets that manage glycemic control and/or contain high fiber may also be helpful under the right circumstances.^[12][3] However, due to the potential variability in underlying causes of RH, these dietary adjustments may not be suitable for everyone.

Treatment approaches may depend on the particular factors that incite hypoglycemic episodes in the person with RH. Pharmaceuticals such as metformin and acarbose may be recommended.^[6][7][16] When RH occurs as a result of gastric bypass surgery, a low-glycemic-index diet along with alpha-glucosidase inhibitors may be considered; if symptoms persist, surgical correction may be warranted.^[2][14][12]

RH is a complex condition, and the exact causes are still not yet understood. After a meal, especially one high in simple carbohydrates, glucose enters the bloodstream, which triggers a release of insulin.^[17] However, in RH, this response is faulty, and hypoglycemia results.^[6][4] The autonomic nervous system is activated when blood glucose drops too low, leading to the signs and symptoms of RH.^[2][4]

RH is defined by its association with meals, but several internal factors may be to blame. Possible causative factors include enlarged insulin-producing islet cells, increased numbers of islet cells, anti-insulin antibodies causing fluctuations in insulin production, altered glucose regulation in the liver, tumors, neuropsychiatric diseases, and digestion/insulin dysfunction (particularly those resulting from gastric surgery).^{[2][18][7][3][10]}