Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and non-eating, ranging from time-restricted feeding daily to alternating days of very low calorie intake. This approach prompts the body to regulate its energy sources, requiring adjustments to blood sugar levels. For most healthy people, the body’s internal systems are highly effective at maintaining stable blood glucose, even during extended periods without food. This article explores the relationship between IF and low blood sugar, known as hypoglycemia, and identifies the specific circumstances where the risk becomes a concern.
Understanding Hypoglycemia and Its Warning Signs
Hypoglycemia is a condition where the amount of glucose in the blood drops below the level needed to fuel the body’s cells, especially the brain. While the precise threshold varies, a blood glucose reading below 70 milligrams per deciliter (mg/dL) is generally considered an alert level. When blood sugar falls too low, the body releases hormones like adrenaline, which trigger physical symptoms.
These warning signs include feeling shaky or tremulous, excessive sweating, and a rapid or irregular heartbeat. As the brain is deprived of its primary fuel source, symptoms can progress to difficulty concentrating, confusion, dizziness, and irritability. Recognizing these early signals is important because an untreated episode can lead to seizures, loss of consciousness, and requires emergency medical attention.
Glucose Homeostasis During Intermittent Fasting
The body maintains a stable supply of glucose to the brain and other organs during fasting through a process called glucose homeostasis. When a fast begins, the body first taps into readily available glucose stores in the liver, stored as glycogen. This process, known as glycogenolysis, is the primary source of glucose during the initial hours of a fast.
As a fast extends beyond 12 to 24 hours, the liver’s glycogen reserves deplete. The body then transitions to a backup mechanism called gluconeogenesis. During gluconeogenesis, the liver, and to a lesser extent the kidneys, synthesize new glucose molecules from non-carbohydrate sources. These precursors include lactate, amino acids derived from muscle protein, and glycerol from fat breakdown.
This metabolic flexibility, driven by hormonal changes like reduced insulin and increased glucagon, ensures a steady, albeit lower, level of glucose is released into the bloodstream. For a healthy individual with a fully functioning liver and endocrine system, this process prevents blood sugar from dropping into the hypoglycemic range, even during extended intermittent fasts.
Specific Risk Factors That Cause Hypoglycemia
While intermittent fasting does not typically cause hypoglycemia in healthy people, it poses a risk for those with pre-existing conditions, particularly diabetes managed with medication. The highest risk occurs in individuals taking insulin or oral medications called sulfonylureas. These drugs force the pancreas to release insulin or enhance glucose uptake, which is dangerous when no food is consumed.
When a person on these medications fasts, the drug continues to drive glucose out of the bloodstream, overriding the body’s natural homeostatic mechanisms. This pharmacological effect can lead to a steep and rapid drop in blood sugar. Fasting increases the rate of hypoglycemia in people with Type 2 diabetes who use these glucose-lowering medications.
Other Contributing Factors
Other factors can exacerbate the risk of low blood sugar during a fast, even without diabetes medication. Strenuous or prolonged exercise while fasted accelerates the utilization of stored glucose and depletes glycogen reserves. Additionally, underlying health issues that affect gluconeogenesis, such as severe liver or kidney disease, can impair the backup system needed to maintain blood glucose during food deprivation.
Safety Measures and Monitoring
Anyone considering intermittent fasting, especially those with a chronic medical condition, should first consult a healthcare provider to assess their personal risk. For individuals with diabetes, this consultation is crucial for adjusting the timing and dosage of glucose-lowering medications. Adjustments are necessary to prevent a drug-induced hypoglycemic event during the fasting window.
Frequent blood glucose monitoring is necessary for those with diabetes who fast, with experts recommending checks every two to four hours when starting the regimen. If hypoglycemia symptoms appear, the fast must be immediately broken. Standard treatment involves consuming approximately 15 grams of a fast-acting carbohydrate, such as glucose tablets, fruit juice, or a tablespoon of honey. Recheck blood sugar levels after 15 minutes to ensure they have returned to a safe range.