Can Not Eating Cause an Insulin Spike? The Dawn Phenomenon Explained

October 28, 2025 •

3 min read

For some individuals, especially those with diabetes, a natural hormonal surge in the early morning can lead to a rise in blood sugar, known as the dawn phenomenon. This can result in an insulin spike, even when no food has been consumed for several hours. Understanding this biological process is key to managing blood glucose levels effectively.

Quick Summary

This article explores the science behind the 'dawn phenomenon', detailing how natural hormonal fluctuations, particularly cortisol and growth hormone, can trigger a spike in blood sugar and subsequent insulin release during fasting. It clarifies this metabolic response for people with and without diabetes, distinguishing it from the Somogyi effect, and offers insights into managing morning hyperglycemia.

Key Points

Normal fasting response: When not eating, the pancreas lowers insulin and releases glucagon to prompt the liver to release stored glucose, keeping blood sugar stable.
The Dawn Phenomenon: For those with diabetes, a natural hormonal surge of cortisol and growth hormone in the early morning can trigger a blood sugar spike, leading to an insulin response.
Cortisol's Role: High levels of cortisol, a stress hormone, increase glucose production and reduce insulin sensitivity, contributing to elevated blood sugar.
Distinguishing the Somogyi Effect: Unlike the dawn phenomenon, the Somogyi effect involves high morning blood sugar resulting from a rebound after an overnight low caused by too much insulin.
Management Strategies: Ways to manage morning spikes include altering medication timing, exercising in the evening, eating earlier dinners, and using CGM for consistent monitoring.
Impact of Intermittent Fasting: For many, intermittent fasting improves insulin sensitivity and lowers fasting insulin levels, but individual hormonal responses should be monitored.
Hormonal Balance: The balance between insulin, glucagon, cortisol, and other hormones is critical for regulating blood sugar, with disruptions leading to metabolic issues.

Understanding the Hormonal Response to Fasting

When you don't eat, your body's energy regulation shifts dramatically. Instead of using glucose from food, your body relies on stored energy reserves. In a healthy individual, this is a well-managed process. As blood glucose levels begin to drop after several hours without food, the pancreas reduces its insulin output. Simultaneously, it increases the secretion of another hormone, glucagon. Glucagon's role is to signal the liver to convert stored glycogen back into glucose and release it into the bloodstream, preventing blood sugar from dropping too low. This is a normal, healthy metabolic function designed to maintain a steady energy supply between meals.

The Dawn Phenomenon and Morning Hyperglycemia

While the baseline hormonal regulation during fasting is designed to keep blood sugar stable, a different process occurs in the early morning hours, particularly for those with diabetes. This is known as the dawn phenomenon, which affects more than 50% of people with type 1 or type 2 diabetes.

Between approximately 3 a.m. and 8 a.m., the body releases a surge of counter-regulatory hormones, including cortisol, growth hormone, and adrenaline. In non-diabetic individuals, the body simply produces enough insulin to counteract this hormonal surge and keep blood sugar stable. However, for those with diabetes, the pancreas either doesn't produce enough insulin or the body is more insulin-resistant. This causes the liver to release more glucose into the bloodstream than the body can manage, resulting in elevated morning blood sugar levels—and a subsequent insulin spike as the body attempts to compensate.

Cortisol and Its Impact on Insulin Sensitivity

Cortisol, often called the 'stress hormone', is a key player in the dawn phenomenon and general glucose regulation. When released, it promotes the production of glucose by the liver and intentionally makes fat and muscle tissues less sensitive to insulin. This mechanism is part of the body's 'fight or flight' response, ensuring quick access to energy. Chronic, long-term stress can keep cortisol levels elevated, leading to a state of sustained insulin resistance, which can worsen glucose control over time and increase the risk of an insulin spike during fasting.

Distinguishing the Dawn Phenomenon from the Somogyi Effect

It is crucial to differentiate the dawn phenomenon from another cause of high morning blood sugar: the Somogyi effect.

Comparison: Dawn Phenomenon vs. Somogyi Effect


Feature	Dawn Phenomenon	Somogyi Effect
Primary Cause	Natural hormonal surge (cortisol, growth hormone) in early morning.	Excessive insulin or medication dose causing overnight hypoglycemia.
Underlying Mechanism	Liver releases more glucose, and the body's insulin response is insufficient.	Body overcompensates for low overnight blood sugar by releasing counter-regulatory hormones.
Timing of Hypoglycemia	No overnight low blood sugar is present.	Hypoglycemia occurs overnight, followed by a rebound high.
Diagnosis	Consistent morning high readings without overnight lows, often detectable with a CGM.	Requires checking blood sugar during the night to identify the preceding low.

How to Address Fasting-Induced Hyperglycemia

Managing morning blood sugar spikes requires a tailored approach, especially for those with diabetes. Strategies often involve lifestyle adjustments and, for some, medication changes.

Eat an earlier dinner: Pushing dinner earlier can prevent an overnight high from a late-night carbohydrate load.
Increase physical activity: Evening exercise can increase insulin sensitivity and help utilize excess glucose.
Adjust medication or insulin timing: Healthcare providers may recommend changing the dose or timing of medication to better manage morning highs.
Monitor blood glucose: Using a continuous glucose monitor (CGM) or checking levels in the early morning can help confirm the pattern and distinguish it from other causes.
Manage stress and sleep: Consistent sleep patterns and stress-reduction techniques (like breathwork or meditation) are essential, as stress hormones directly impact glucose regulation.

Conclusion

Ultimately, the question of whether not eating can cause an insulin spike has a nuanced answer. While fasting typically leads to lower insulin levels, a pre-dawn hormonal surge can cause the liver to release glucose, triggering a compensatory insulin response, especially in people with diabetes. This physiological reaction, known as the dawn phenomenon, is distinct from other metabolic issues and requires specific management strategies. By understanding the intricate hormonal interplay, individuals can work with their healthcare providers to effectively regulate blood sugar and improve metabolic health.

Visit the International Diabetes Federation for more information on managing diabetes and fasting.

Frequently Asked Questions

The 'dawn phenomenon' is a natural hormonal event where a surge of hormones, like cortisol and growth hormone, is released in the early morning (around 3 a.m. to 8 a.m.), causing the liver to produce more glucose. For people with diabetes, whose bodies cannot produce or use insulin effectively, this leads to a spike in blood sugar and a subsequent insulin response, even when fasting.

While fasting typically lowers blood sugar, a rise can occur due to the release of hormones that stimulate the liver to convert stored glycogen into glucose. For some, especially those with diabetes, this hormonal action in the early morning hours can cause an increase in blood glucose that their body cannot regulate efficiently, leading to a rise in blood sugar.

If left unmanaged, the consistent morning high blood sugar from the dawn phenomenon can contribute to higher A1C levels over time, increasing the risk of long-term diabetes complications such as heart disease, kidney disease, and neuropathy. Consistent management is important for overall health.

The dawn phenomenon is a rise in morning blood sugar caused by a natural hormonal surge, without a preceding low. The Somogyi effect, in contrast, is a rebound high caused by the body overcompensating for an episode of low blood sugar that occurred overnight, typically from too much injected insulin.

For most people, intermittent fasting, particularly longer fasts, can significantly lower insulin levels and improve insulin sensitivity over time. However, the dawn phenomenon can still occur in the early morning regardless of whether you are fasting. Some studies also note a temporary cortisol spike in longer fasts, though benefits generally outweigh this for improved sensitivity.

Cortisol, the stress hormone, promotes the production of glucose by the liver and reduces the body's sensitivity to insulin. This helps provide a quick energy source during times of stress. Chronic stress can keep cortisol levels high, contributing to sustained insulin resistance and higher fasting blood glucose levels.

Common symptoms of the dawn phenomenon include consistently high blood sugar readings in the early morning, increased thirst, frequent urination, headaches, and blurred vision upon waking. Monitoring is necessary to confirm the cause of morning high blood sugar.

The hormonal surge that causes the dawn phenomenon occurs in everyone. However, in people without diabetes, the pancreas responds by producing enough insulin to counteract the effect, preventing a significant rise in blood sugar. The spike and subsequent insulin response are problematic primarily for those with impaired insulin regulation.