Does Low-Carb Cause High Cortisol? Unpacking the Science of Diet and Stress

October 14, 2025 •

3 min read

According to a 2022 meta-analysis, low-carbohydrate diets can moderately increase resting cortisol levels during the first three weeks of implementation. This initial spike, however, does not always reflect a long-term issue, as the body undergoes metabolic adaptation, bringing resting cortisol back to baseline for many individuals. Understanding this nuanced relationship is key to determining if a low-carb diet is the right approach for your body and stress levels.

Quick Summary

This article explains the temporary rise in cortisol on a low-carb diet, its metabolic purpose, and how to manage stress while restricting carbohydrates. It examines short-term and long-term hormonal responses, the effect of exercise, and other influencing factors. It also addresses the misconception that all low-carb diets cause chronic stress.

Key Points

Initial Increase: Resting cortisol levels can rise moderately during the first few weeks of a low-carb diet as the body adapts to burning fat for fuel.
Long-Term Normalization: After approximately three weeks, resting cortisol levels typically return to baseline as the body becomes efficient at using ketones for energy.
Elevated Post-Exercise Response: Even after adaptation, post-exercise cortisol remains higher on a low-carb diet, especially following prolonged endurance exercise.
Stress Mitigation: Factors like sleep, hydration, and other psychological stressors significantly influence overall cortisol levels and can be managed to support hormonal balance.
Individual Variation: The hormonal response is not uniform; very-low-carb diets and high-protein versions can cause more pronounced effects than moderate low-carb plans.
Strategic Fueling: Athletes on a low-carb diet can consider strategic carbohydrate intake around intense workouts to help mitigate the post-exercise cortisol spike.

The link between a low-carbohydrate diet and cortisol is a topic of significant interest and some confusion. Cortisol, often called the “stress hormone,” plays a crucial role in managing the body's stress response and regulating glucose metabolism. When carbohydrate intake is severely restricted, the body's primary fuel source shifts, leading to temporary metabolic stress and an initial elevation in cortisol levels. However, the story is more complex than a simple cause-and-effect relationship.

The Science Behind the Cortisol Spike

Restricting carbohydrates causes the body to seek alternative fuel sources. This can trigger the release of cortisol, which aids in gluconeogenesis – the creation of glucose from non-carbohydrate sources like protein. This helps ensure organs like the brain have sufficient energy. This initial metabolic shift is a normal, temporary response and is part of the adaptation phase to a low-carb diet.

A 2022 systematic review found that resting cortisol moderately increased during the first three weeks of a low-carb diet but returned to normal for most people after this period. This suggests the body adapts to using fat and ketones for fuel, reducing the need for elevated cortisol.

Exercise and Its Impact on Cortisol

While resting cortisol tends to normalize, exercise on a low-carb diet can lead to a different response. The same 2022 meta-analysis observed higher post-exercise cortisol, especially after prolonged activity. This might be due to several factors:

Low glycogen stores necessitating more cortisol for gluconeogenesis and fat oxidation during long exercise.
Cortisol promoting fat breakdown for fuel.
Increased cortisol to help preserve glucose for brain function as muscles use more during exercise.

Athletes on a low-carb diet should consider this sustained post-exercise cortisol response, particularly with high-volume training.

Individual Differences and Other Stressors

Individual responses to low-carb diets vary based on factors like the degree of carb restriction, protein intake, and other lifestyle stressors.

Key considerations:

More restrictive diets may cause more significant hormonal changes.
High-protein low-carb diets (over 35% protein) can lead to more pronounced hormonal effects, potentially adverse, compared to moderate-protein versions.
Combining a low-carb diet with other stressors like poor sleep or chronic psychological stress can exacerbate hormonal responses.

Managing Cortisol on a Low-Carb Diet

If you're concerned about cortisol levels on a low-carb diet, these strategies can help:

Prioritize 7-9 hours of quality sleep to regulate circadian rhythms and cortisol.
Consider strategically timing some carbohydrate intake around intense workouts, especially for active individuals.
Ensure adequate calorie intake from healthy fats and protein to avoid adding caloric restriction as another stressor.
Utilize stress-reduction techniques like meditation or yoga.
Include healthy fats like avocado and olive oil, which can positively impact cortisol.

Low-Carb Diet and Cortisol: Comparison of Short-Term vs. Long-Term Effects


Aspect	Short-Term (< 3 weeks)	Long-Term (≥ 3 weeks)
Resting Cortisol	Moderately increased due to metabolic stress.	Returns to baseline levels once adaptation is complete.
Post-Exercise Cortisol	Higher response, especially after long-duration exercise.	Remains elevated compared to high-carb diets, though possibly less acutely.
Energy Source	Shift from glucose to ketones begins, leading to initial withdrawal symptoms.	Body becomes efficient at using fat and ketones for fuel.
Overall Feeling	Potential for "keto flu" symptoms like fatigue, headache, and irritability.	Often characterized by stable energy levels and reduced cravings.

Conclusion

The impact of a low-carb diet on cortisol is dynamic. While a temporary rise in resting cortisol is common during the initial adaptation phase, levels typically normalize within weeks. However, the cortisol response to exercise may remain elevated. Individual factors and other stressors also play a significant role. Managing sleep, overall stress, and strategically planning for exercise can support hormonal balance. Consulting a healthcare professional is recommended before making significant dietary changes. For more information on managing stress and diet, resources like the MD Anderson Cancer Center article “8 foods that impact stress” can be helpful.

Frequently Asked Questions

A low-carb diet initially increases cortisol because the body perceives the lack of its primary fuel (glucose) as a form of metabolic stress. Cortisol is released to promote gluconeogenesis, the process of creating new glucose from protein, to ensure the brain has enough energy.

No, for most people, resting cortisol levels do not stay elevated long-term. After the initial adaptation phase (around three weeks), the body becomes efficient at using ketones for fuel, and resting cortisol levels generally return to baseline.

Yes, research shows that post-exercise cortisol levels are higher on a low-carb diet, particularly after long-duration exercise. This is likely due to the body's need to facilitate fat oxidation and preserve glucose for the brain during prolonged physical activity.

Yes, high-protein, low-carb diets (≥35% of calories from protein) have been shown to cause more significant hormonal shifts, including potentially adverse endocrine effects, compared to moderate-protein low-carb diets.

To manage cortisol, focus on good sleep hygiene, stress reduction techniques like meditation, staying adequately hydrated, and ensuring sufficient calorie intake. Some individuals may benefit from strategically timing carbohydrate intake around intense exercise.

No, the degree of impact can vary. Very low-carb or ketogenic diets tend to have a more pronounced initial effect on cortisol levels compared to more moderate low-carb approaches.

Combining severe calorie restriction with a low-carb diet can increase metabolic stress and lead to elevated cortisol levels. This can potentially slow metabolism and hinder weight loss efforts.