Does Undereating Increase Cortisol? The Link Between Caloric Restriction and Stress

October 12, 2025 •

4 min read

Research has consistently shown a link between caloric restriction and increased cortisol production, a primary stress hormone. This article explores the physiological mechanisms behind this phenomenon and how undereating can significantly impact the body's stress response system.

Quick Summary

Caloric restriction, particularly severe or prolonged undereating, activates the body's stress response, leading to elevated cortisol levels. This hormonal shift affects metabolism, promotes fat storage, and disrupts blood sugar control, ultimately hindering weight loss efforts and compromising overall health.

Key Points

Undereating Increases Cortisol: Severe or chronic caloric restriction triggers the body's stress response (HPA axis), leading to elevated levels of the stress hormone, cortisol.
Cortisol Promotes Fat Storage: Chronically high cortisol levels contribute to increased fat storage, especially visceral fat around the abdomen.
Metabolism Slows Down: Undereating and high cortisol can suppress thyroid function and metabolic rate as the body enters a protective 'famine' mode.
Appetite Hormones Imbalanced: The stress response from undereating increases hunger hormones (ghrelin) and decreases satiety hormones (leptin), driving increased cravings and hunger.
Sleep is Disrupted: Elevated cortisol in the evening can interfere with the natural sleep-wake cycle, leading to insomnia and poor sleep quality.
Muscle Loss is Accelerated: Cortisol's catabolic effects can break down muscle tissue for energy during caloric restriction, hindering body composition goals.
Balanced Diet is Crucial: Counteract the cortisol spike by consuming a nutrient-dense diet rich in magnesium, vitamin C, and omega-3s, and avoid excessive restriction.

The Body's Survival Response: Why Undereating Raises Cortisol

In prehistoric times, a lack of food triggered the body's survival mechanisms. The hypothalamic-pituitary-adrenal (HPA) axis, our central stress response system, would activate, flooding the body with cortisol to help cope with the perceived 'famine'. While modern undereating is often intentional, driven by dieting, the body's ancient response remains the same. When a person restricts calories significantly, especially over a prolonged period, the body perceives this as a threat to survival. The adrenal glands, prompted by the HPA axis, increase cortisol production to ensure a ready supply of glucose for the brain.

This elevation of cortisol, while an essential survival function, has several negative consequences in the context of modern dieting. Chronically high cortisol levels can promote weight gain, particularly around the midsection, and lead to other health issues such as insulin resistance and impaired immune function.

The Vicious Cycle: Cortisol, Metabolism, and Appetite

When undereating elevates cortisol, it creates a feedback loop that makes sustained dieting difficult. High cortisol levels can increase cravings for high-calorie, high-sugar foods, making it harder to stick to a restricted diet. This can trigger cycles of restriction followed by overeating or bingeing, which further destabilizes hormones and metabolic processes.

Furthermore, the increase in cortisol is often accompanied by other hormonal changes. The body's thyroid function can be suppressed, leading to a slower metabolism as the body tries to conserve energy. Simultaneously, hunger hormones like ghrelin increase while satiety hormones like leptin decrease, amplifying feelings of hunger and making it even harder to control food intake.

Cortisol's Impact on Different Bodily Functions

Blood Sugar and Insulin: Cortisol counteracts insulin, causing a rise in blood sugar levels. This can lead to decreased insulin sensitivity over time and increase the risk of developing type 2 diabetes.
Fat Storage: Elevated cortisol promotes the storage of visceral fat, the dangerous fat that accumulates around abdominal organs. This is a survival mechanism to save energy stores for the perceived emergency.
Muscle Mass: Cortisol has catabolic effects, meaning it breaks down tissues for energy. In a state of undereating, cortisol can cause the body to break down muscle tissue to convert its amino acids into glucose, leading to muscle wasting.
Sleep Quality: As cortisol naturally peaks in the morning and dips at night, chronic stress from undereating can disrupt this circadian rhythm. Elevated evening cortisol levels can interfere with sleep onset and quality, contributing to insomnia and a feeling of being 'wired but tired'.

The Difference Between Acute Fasting and Chronic Undereating

While both fasting and chronic undereating involve calorie restriction, the body's response can differ depending on the duration and severity.


Feature	Acute Fasting (e.g., 24-48 hours)	Chronic Undereating (long-term, moderate-to-severe deficit)
Cortisol Response	Often shows a sharp, but transient, increase in cortisol levels.	Leads to a persistent, chronically elevated cortisol output.
Metabolic Shift	Body adapts by increasing gluconeogenesis and ketogenesis to provide fuel.	Can lead to a metabolic slowdown and suppression of thyroid function to conserve energy.
Fat Storage	Minimal impact, as the body is mobilizing energy stores for immediate use.	Promotes visceral fat storage, driven by chronically high cortisol and metabolic resistance.
Hormonal Adaptation	Hormones like ghrelin and leptin fluctuate temporarily.	Causes long-term imbalances in appetite and sex hormones, often contributing to fatigue and weight regain.
Psychological Impact	Can cause temporary stress and mood changes, often manageable.	Associated with increased anxiety, irritability, and potential development of eating disorders.

How to Mitigate the Cortisol Spike During a Deficit

If a caloric deficit is necessary for health reasons, it is possible to manage the cortisol response to minimize negative effects. This is not about 'beating' the stress response but rather working with your body in a healthier way.

Prioritize Nutrient-Dense Foods: A balanced diet rich in fruits, vegetables, lean proteins, and healthy fats provides the body with the necessary nutrients to function without triggering a famine response. Key nutrients like magnesium, vitamin C, and omega-3 fatty acids can help regulate cortisol.
Manage Stress Levels: Incorporate mindfulness, meditation, yoga, or other relaxation techniques to actively lower stress. Since the body perceives both physical and emotional stress similarly, addressing the psychological component is crucial.
Focus on Adequate Sleep: Cortisol levels naturally decrease at night, but insufficient or poor-quality sleep keeps them elevated. Establishing a consistent sleep schedule and optimizing your sleep environment can significantly help.
Don't Fear Carbohydrates: Particularly during caloric restriction, adequate carbohydrate intake can prevent a crash in blood sugar that would otherwise prompt a cortisol release. Balanced macronutrient intake is key.
Moderate Exercise: While regular exercise helps manage stress, excessive or high-intensity workouts during a caloric deficit can further increase cortisol. Opt for moderate, consistent activity to support your body without overtaxing it.

Conclusion

Undereating is a significant stressor on the body, triggering an evolutionary survival mechanism that elevates cortisol levels. This can lead to a vicious cycle of hormonal imbalance, weight plateaus, and increased cravings, sabotaging long-term health and weight management goals. By understanding this complex relationship, individuals can adopt a more mindful and sustainable approach to nutrition. Instead of severe restriction, focusing on a balanced, nutrient-dense diet, incorporating stress-reducing practices, and prioritizing sleep offers a more effective pathway to improved metabolic health and well-being.

For more information on the endocrine system and stress response, you can explore the comprehensive physiology resources provided by the National Center for Biotechnology Information (NCBI) on their website.

Frequently Asked Questions

Yes, dieting can raise your cortisol levels, especially if the calorie deficit is too severe or prolonged. The body perceives significant calorie restriction as a form of stress, activating the HPA axis to increase cortisol production.

High cortisol can hinder weight loss by promoting visceral fat storage, slowing metabolism, and increasing cravings for high-calorie foods. It can create a vicious cycle where dieting leads to higher cortisol, which in turn makes further weight loss more difficult.

Beyond weight-related issues, high cortisol from undereating can lead to poor sleep, anxiety, mood swings, insulin resistance, and accelerated muscle tissue breakdown.

To lower cortisol while dieting, focus on a moderate, rather than extreme, calorie deficit. Prioritize stress management techniques like mindfulness, ensure adequate sleep, and consume a nutrient-dense, balanced diet rich in fruits, vegetables, and healthy fats.

Yes. While short-term fasting can cause a temporary spike in cortisol, chronic undereating leads to persistently high levels. The body's hormonal and metabolic adaptations to these two states are different.

Yes, it can. Chronically high cortisol levels trigger physiological responses that promote fat storage, especially in the abdominal area, and can disrupt appetite and metabolism, potentially leading to weight gain.

Yes, prolonged undereating can lead to deficiencies in key nutrients like magnesium, vitamin C, and B vitamins, all of which are important for regulating the body's stress response and adrenal function.