The ketogenic diet, characterized by very low carbohydrate intake, high fat consumption, and moderate protein, shifts the body’s primary fuel source from glucose to fat-derived ketones. While this metabolic state, known as ketosis, stabilizes blood sugar, it can sometimes lead to an unexpected drop in blood glucose, a condition called hypoglycemia. Hypoglycemia is generally defined as a blood sugar reading below 70 mg/dL. Understanding how to prevent it is paramount for safely maintaining a ketogenic lifestyle, focusing on metabolic stability rather than constant carbohydrate dosing.
Understanding Blood Sugar Regulation on Keto
The primary reason hypoglycemia is a concern on a ketogenic diet is the dramatic reduction in circulating glucose and the resulting low insulin levels. Since dietary carbohydrates are largely eliminated, the body relies on the liver to produce a small, steady supply of glucose through a process called gluconeogenesis. This mechanism maintains a lower baseline blood glucose level, often in the 70–90 mg/dL range, which is normal for a keto-adapted state. True hypoglycemia occurs when this baseline drops too far, usually due to an external factor interfering with the body’s counter-regulatory response. For individuals taking glucose-lowering medication, this is called iatrogenic hypoglycemia, which is a significant safety risk. The state of nutritional ketosis itself offers a protective effect, as the brain uses ketones for fuel. Nevertheless, if blood sugar drops severely, the body’s normal defensive reaction, which includes releasing the hormone glucagon, may be blunted on a keto diet, making prevention essential.
Dietary Strategies for Preventing Low Glucose
Maintaining metabolic stability through strategic eating is the most effective preventative measure against low blood sugar. This starts with ensuring consistency in the amount and timing of the small number of carbohydrates consumed daily. Limiting total net carbohydrate intake to a personalized threshold, typically 20 to 50 grams per day, prevents the sharp insulin spikes that can lead to a subsequent blood sugar crash.
It is also important to consume adequate dietary fat, which provides the substrate for ketone production and promotes satiety, helping to stabilize energy levels throughout the day. Furthermore, protein intake should be moderate, as excessive protein can be converted to glucose through gluconeogenesis, potentially triggering an unwanted insulin response.
Electrolyte balance plays an often-overlooked role, as low insulin levels on a ketogenic diet cause the kidneys to excrete more water and minerals, particularly sodium and potassium. Symptoms of electrolyte depletion, such as lightheadedness, fatigue, and muscle weakness, can often be mistaken for low blood sugar. Proactively supplementing with sodium, potassium, and magnesium can resolve these symptoms and support overall metabolic function.
Adjusting Activity and Medication
Individuals using glucose-lowering medication, such as insulin or sulfonylureas, must work closely with a healthcare professional before and during the adoption of a ketogenic diet. The diet is so effective at lowering blood glucose that continuing medication at the previous dosage presents a very high risk of iatrogenic hypoglycemia. Medication dosages, particularly insulin, often need to be proactively reduced by 50% or more immediately upon starting the diet to prevent dangerous lows.
Exercise is another factor that requires careful management, as physical activity increases glucose uptake by the muscles. For those prone to lows, timing exercise appropriately is key. Generally, post-meal activity, such as a light walk after eating, is beneficial as it helps reduce the small postprandial glucose rise and improves insulin sensitivity.
It is advisable to avoid intense or prolonged aerobic exercise late in the evening, as this can deplete remaining glycogen stores and increase the risk of nocturnal hypoglycemia. Individuals who rely on medication should monitor blood sugar before and after exercise and may need to reduce insulin doses or consume a small, fast-acting carbohydrate before a strenuous workout. For those on SGLT2 inhibitors, consultation with a physician is important, as this class of medication can increase the risk of euglycemic diabetic ketoacidosis when carbohydrate intake is severely restricted.
Recognizing and Treating Acute Episodes
Even with careful prevention, acute hypoglycemia can still occur, and recognizing the symptoms is the first step toward effective management. Common signs include shakiness, sweating, dizziness, confusion, and a rapid heartbeat. For a person in ketosis, the standard definition of hypoglycemia (below 70 mg/dL) still applies, though symptoms can sometimes be milder because the brain utilizes ketones for energy.
When symptoms occur, the immediate treatment requires a modified version of the standard “15-15 rule.” The goal is to ingest the minimal amount of fast-acting glucose necessary to raise blood sugar without disrupting ketosis significantly. This typically means consuming 5 to 10 grams of pure glucose, such as one or two glucose tablets, rather than the standard 15 grams. Glucose tablets are preferable to juice or candy bars because they contain pure dextrose, which absorbs rapidly and allows for precise dosing. After consuming the glucose, wait 15 minutes and re-check the blood sugar level. If the level is still below 70 mg/dL, repeat the small dose. Once blood glucose is stabilized, consuming a small amount of fat and protein can help prevent a subsequent drop.