Does keto spike cortisol? A detailed look at the diet's effect on stress hormones

October 14, 2025 •

4 min read

Research shows that short-term ketogenic diets can temporarily increase resting and post-exercise cortisol levels during the first few weeks of adaptation. But does keto spike cortisol long-term, or does it eventually normalize? Understanding this hormonal response is key to a successful keto journey and managing potential side effects.

Quick Summary

The ketogenic diet can cause a temporary rise in cortisol during the initial adaptation period as the body adjusts to using fat for fuel. However, these levels typically normalize over time with sustained ketosis. Individual responses vary, influenced by factors like electrolyte balance, overall stress, and exercise intensity.

Key Points

Initial Spike is Normal: During the first 1-3 weeks of keto, cortisol can increase as the body switches from using carbs to fat for fuel.
Normalization Occurs: For most, resting cortisol levels return to normal or even decrease after the initial adaptation period.
Electrolytes are Crucial: Inadequate sodium intake can trigger adrenal stress and increase cortisol, so proper electrolyte balance is essential.
Exercise Matters: Post-workout cortisol may remain higher on a low-carb diet due to depleted glycogen stores, but moderation can help.
Caution for Adrenal Issues: Individuals with existing adrenal fatigue may find that keto adds too much stress and should approach the diet with caution.
Supportive Strategies Work: Practices like getting adequate sleep, managing stress, and proper hydration are key to minimizing negative hormonal responses on keto.
Individual Responses Vary: Hormonal reactions to the ketogenic diet are not universal and are highly dependent on individual health, genetics, and lifestyle factors.

The Initial Cortisol Spike: The 'Keto Flu' Phase

During the initial phase of transitioning to a ketogenic diet, many people experience a cluster of symptoms known as the 'keto flu'. These can include headaches, fatigue, and irritability, and are often accompanied by a temporary increase in the stress hormone cortisol. This initial spike is a normal physiological response as your body adjusts from burning glucose to primarily using fat and ketones for energy.

There are a few reasons for this early hormonal shift:

Energy Switch: With limited carbohydrates, the body needs a fallback mechanism to maintain blood sugar levels for critical functions, particularly for the brain. It does this by increasing gluconeogenesis (the creation of new glucose) from protein, a process driven by cortisol.
Adaptive Stress: The metabolic shift to ketosis is a form of adaptive stress on the body. For some, especially those who are already stressed, this can be an added burden that triggers a more pronounced cortisol response.
Dehydration and Electrolyte Loss: When you first restrict carbs, your body sheds water and with it, important electrolytes like sodium. A significant drop in sodium can signal the adrenal glands to increase cortisol, alongside other fluid-regulating hormones.

Why Hydration and Electrolytes Are Critical

Maintaining proper hydration and electrolyte levels is one of the most effective ways to mitigate the initial cortisol spike. A diet with adequate sodium will likely not alter cortisol to a significant extent, while salt restriction during a ketogenic diet can cause adrenal stress. Simple strategies can make a big difference, such as:

Adding extra salt to your food.
Consuming electrolyte-rich bone broth.
Including mineral-rich foods like avocados, spinach, and leafy greens in your meals.

Long-Term Effects on Cortisol Levels

Fortunately, for most individuals, the initial elevation in cortisol is temporary. Studies show that resting cortisol levels tend to return to baseline or may even decrease after the initial adaptation phase, which typically lasts around three weeks. Once the body becomes 'fat-adapted' and efficiently uses ketones for fuel, the constant demand for gluconeogenesis decreases.

Stable Energy Source: Ketones provide a stable and consistent energy source for the brain and body, which can reduce the need for cortisol spikes to regulate blood sugar.
Potential for Reduced Stress: Some research suggests that long-term, well-formulated ketogenic diets can actually have a positive effect on stress control and mood. This may be due to the diet's ability to modulate certain neuroendocrine systems and provide a more stable emotional state.

Managing Post-Workout Cortisol

One area where cortisol can remain elevated even after the adaptation phase is post-exercise. Research indicates that during workouts on a low-carb diet, cortisol levels may increase more compared to other diets. This is likely due to the body relying on cortisol to facilitate gluconeogenesis and lipolysis (fat breakdown) to fuel the activity, especially when muscle glycogen stores are low.

Exercise Moderation: Individuals can manage this by moderating exercise intensity, particularly during the initial adaptation period. Avoid overtraining, which can be a significant stressor on the body and potentially exacerbate cortisol issues.
Strategic Carbohydrates: For some athletes, strategies like carb cycling—incorporating carbs on workout days—can help manage hormonal balance and reduce post-exercise cortisol.

Who Needs to be Cautious? Adrenal Concerns

While keto can be beneficial for many, it’s not suitable for everyone, especially those with pre-existing adrenal issues. For individuals already dealing with chronic stress or adrenal dysfunction, the initial stress of a strict ketogenic diet can be too much for their system to handle, potentially worsening their symptoms.

HPA Axis Dysfunction: The hypothalamic-pituitary-adrenal (HPA) axis regulates the body's stress response. If this system is already overworked, introducing a drastic dietary change like keto can be an additional stressor.
Easing In: For those with adrenal concerns, a slower, more gradual transition into a lower-carb diet is often recommended over an abrupt switch to keto.

How to Support Adrenal Health on Keto

For a smoother transition and better long-term success, consider these tips:

Prioritize Sleep: Aim for 7-9 hours of quality sleep nightly, as sleep is crucial for regulating cortisol and stress hormones.
Manage Stress: Incorporate mindfulness, meditation, or other relaxation techniques into your daily routine.
Balance Macros: Ensure you are not undereating. Inadequate calorie intake is a stressor that can keep cortisol levels high.
Consider Carb Cycling: For some, especially women, cycling carbs strategically can reduce hormonal stress.

Cortisol Response: Short-Term vs. Long-Term Keto


Factor	Short-Term Keto (Adaptation Phase)	Long-Term Keto (Fat-Adapted)
Cortisol Levels	Temporarily elevated (resting and post-exercise)	Generally normalized or decreased (resting)
Energy Source	Transitioning from glucose to ketones.	Primariy utilizing fat and ketones for fuel.
Primary Stressor	Metabolic stress from restricting carbohydrates.	Minimal metabolic stress.
Gluconeogenesis	Higher demand for new glucose creation.	Reduced demand for new glucose.
Electrolytes	Increased risk of depletion due to water loss.	Stability depends on consistent, adequate intake.

Conclusion

While it is true that the ketogenic diet can cause a temporary spike in cortisol, this effect is largely confined to the initial adaptation phase and is a natural part of the body’s metabolic transition. With proper management of electrolytes, hydration, and overall stress, resting cortisol levels typically normalize in the long run. However, the response is highly individual and can be influenced by factors like exercise intensity and pre-existing adrenal conditions. For those with adrenal concerns, a gradual approach may be a safer path. By understanding these dynamics, individuals can better navigate the dietary changes and achieve a more balanced and sustainable approach to their health. Consulting a healthcare professional is always advised before starting any restrictive diet, especially if you have hormonal or adrenal issues.

Frequently Asked Questions

A ketogenic diet can temporarily increase cortisol because your body interprets the severe carbohydrate restriction as a mild stressor, especially during the initial adaptation phase. Cortisol is released to help produce new glucose through gluconeogenesis to fuel essential organs like the brain, as it is still adjusting to using ketones.

The initial cortisol spike on keto typically subsides after the first few weeks as the body becomes 'fat-adapted.' Studies show that resting cortisol levels generally normalize after about three weeks for most individuals.

While temporary, high cortisol can potentially hinder weight loss by increasing appetite and promoting fat storage, especially visceral fat. However, this effect is often temporary. For long-term success, managing overall stress and supporting hormonal balance is key.

During the initial phase of keto, the body loses more water and electrolytes. Low sodium levels, in particular, can prompt the adrenal glands to release more cortisol and other hormones, adding to stress. Ensuring adequate electrolyte intake helps regulate fluid balance and reduce this stress response.

Individuals with pre-existing adrenal issues should be cautious with the keto diet. The initial stress of the metabolic shift can exacerbate an already stressed system. A gradual transition or a less restrictive low-carb approach may be more appropriate for those with adrenal concerns.

Yes, some evidence suggests that women may experience a sharper cortisol response, particularly during the initial adaptation, possibly influenced by factors like caloric intake and over-exercising. Individual hormonal differences mean the response can vary significantly.

Once fat-adapted, a stabilized cortisol level can support better sleep. Studies have also shown that a keto diet can potentially increase deep sleep and lead to improvements in overall sleep quality. However, some individuals may experience temporary insomnia during the initial phase.