Does Low Carb Diet Affect Cortisol Levels? An In-Depth Look at the Hormonal Impact

October 29, 2025 •

3 min read

According to a 2022 systematic review and meta-analysis, resting cortisol levels can moderately increase during the first three weeks of a low-carbohydrate diet. This finding prompts a critical question for many dieters and fitness enthusiasts: Does low carb diet affect cortisol levels? The answer is nuanced, depending on diet duration, exercise, and individual factors.

Quick Summary

A low-carb diet can cause an initial, short-term increase in resting cortisol during the adaptation phase. While long-term resting levels typically normalize, post-exercise cortisol can remain elevated. The body uses cortisol for glucose regulation in the absence of carbohydrates, and this hormonal response can be influenced by diet severity, protein intake, and physical activity levels.

Key Points

Initial cortisol spike is common: During the first three weeks of a low-carb diet, resting cortisol can increase as the body adapts to glucose restriction.
Long-term resting cortisol normalizes: After the initial adaptation period (around 3 weeks), resting cortisol levels tend to return to baseline.
Post-exercise cortisol remains elevated: Even with long-term low-carb adherence, the hormonal stress response to exercise, especially long-duration activity, is higher.
The body uses cortisol for glucose production: Cortisol is released to facilitate gluconeogenesis (creating glucose from protein) when carbohydrates are scarce.
Diet severity, protein intake, and activity matter: The extent of the cortisol effect is influenced by how strict the carb restriction is, the amount of protein consumed, and the type of exercise performed.
Management is possible: Strategies like prioritizing sleep, timing carbs, and practicing relaxation techniques can help manage cortisol on a low-carb diet.

Understanding the Link Between Low-Carb Diets and Cortisol

Cortisol, produced by the adrenal glands, is known as the “stress hormone” and is crucial for regulating metabolism, blood sugar, and inflammation. Restricting carbohydrates, the body's primary energy source, can be perceived as physiological stress, leading the body to release cortisol.

The Short-Term vs. Long-Term Cortisol Response

Studies indicate that the body's cortisol response to a low-carb diet changes over time.

Initial Spike (Short-Term): During the first few weeks, especially with very low-carb or ketogenic diets, the body increases gluconeogenesis (creating glucose from non-carbohydrate sources). A 2022 meta-analysis showed a moderate increase in resting cortisol during this initial three-week period. This spike is part of the body's adaptation.
Normalization (Long-Term): After about three weeks, as the body adapts to using fats and ketones for fuel, resting cortisol levels often return to near normal. However, this normalization doesn't apply equally to all situations.

The Lingering Effect on Post-Exercise Cortisol

Even after adapting to a low-carb diet, exercise can trigger a different hormonal response. Post-exercise cortisol levels can remain elevated, especially after prolonged or intense activity. Lower glycogen stores on a low-carb diet mean less readily available energy for intense exercise. Cortisol aids in gluconeogenesis during and after exercise to provide glucose to the brain and promotes the breakdown of fats to support energy needs. This suggests that exercise on a low-carb diet can involve a higher degree of metabolic stress compared to a higher-carbohydrate diet.

Factors That Influence the Low-Carb and Cortisol Relationship

The impact of a low-carb diet on cortisol varies based on several factors, including the severity of restriction, protein intake, physical activity, and potentially gender. Stricter diets, high protein intake alongside low carbs, and frequent intense exercise are associated with more pronounced hormonal changes.

How to Mitigate Elevated Cortisol on a Low-Carb Diet

To manage cortisol while on a low-carb diet, consider strategies such as prioritizing 7–9 hours of sleep nightly, practicing stress reduction techniques like meditation, optimizing macronutrient intake, and choosing nutrient-dense foods. Consuming a moderate amount of carbohydrates strategically may also help manage cortisol levels.

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


Feature	Short-Term (<3 weeks)	Long-Term (≥3 weeks)
Resting Cortisol	Increases moderately during the initial adaptation period.	Returns to or near baseline levels after the body adapts.
Post-Exercise Cortisol	Increases significantly more than on a high-carb diet, especially after longer exercise.	Remains elevated after exercise, suggesting continued metabolic stress during activity.
Hormonal Driving Force	Body perceives carb restriction as stress, uses cortisol for glucose regulation (gluconeogenesis).	Body adapts to ketosis, reducing the need for gluconeogenesis and stabilizing resting cortisol.
Metabolic State	Transition period, potential fatigue, mood swings, and "keto flu" symptoms.	Adapted state (ketosis), but still altered hormonal response to physical activity.

Conclusion

While a low-carbohydrate diet can initially increase resting cortisol, this generally normalizes as the body adapts. However, the cortisol response to exercise may remain elevated. This suggests a level of metabolic stress from low-carb diets that is influenced by exercise intensity, diet strictness, and individual factors. To manage potential cortisol issues, prioritize sleep, manage stress, and focus on a nutrient-rich, balanced approach to low-carb eating. Consulting a healthcare professional before major dietary changes is recommended. For more information, {Link: PubMed pubmed.ncbi.nlm.nih.gov/35254136/} provides an overview.

Frequently Asked Questions

A low-carb diet typically causes a temporary increase in resting cortisol during the initial weeks, but this does not usually lead to chronically high resting cortisol long-term. However, a constant elevation of cortisol could result from sustained, severe calorie restriction, excessive exercise, or psychological stress combined with a restrictive diet.

Yes, the severity of carbohydrate restriction affects the cortisol response. Very low-carb or ketogenic diets often trigger a more significant hormonal shift than more moderate low-carb plans. A high-protein low-carb diet can also have different hormonal effects compared to a moderate-protein version.

To lower cortisol on a low-carb diet, prioritize adequate sleep, reduce psychological stress through relaxation techniques like meditation or yoga, ensure a well-balanced diet rich in nutrients like magnesium and omega-3s, and time your exercise and meals effectively.

For most people, a very small amount of carbohydrates can be beneficial, particularly for active individuals. Strategic timing of carbs, such as eating them post-workout or in the evening, can help manage cortisol and support recovery without compromising the benefits of a low-carb approach.

Signs of a negative cortisol response can include persistent fatigue, poor sleep quality, mood swings, increased anxiety, stalled weight loss despite a calorie deficit, and a 'wired but tired' feeling. If you experience these symptoms, it's wise to evaluate your diet and lifestyle.

Yes, exercise, particularly long-duration or high-intensity activity, causes a higher and more prolonged cortisol spike on a low-carb diet compared to a high-carb diet. This is due to the body's need for glucose during exertion and its reliance on cortisol to produce it.

The term "adrenal fatigue" is not a medically recognized diagnosis, though it is used colloquially. The correct medical term for dysregulation of the HPA axis due to chronic stress is HPA axis dysfunction. While low-carb diets can act as a stressor, more evidence is needed to confirm a direct link to chronic HPA axis issues from dieting alone.