The mental benefits of prolonged fasting

Prolonged fasting is the voluntary abstinence from food for more than 24 hours. This form of intermittent fasting has received a lot of attention in recent years. The focus is often on physical effects such as weight loss and metabolic health. But there is also growing scientific interest in what fasting does to the mind.

Two major review studies show that the psychological impact of fasting is complex: it can have both positive effects on mood, stress, and cognition, as well as risks depending on context and individual factors.[1][2]

In this blog we briefly explore that nuance: what are the real psychological benefits of prolonged fasting and where are its limits?

Mood and depressive symptoms: small but consistent improvements

One of the most studied effects of fasting is its influence on mood. Both clinical studies and meta-analyses show that fasting can lead to improvements in depressive symptoms and overall well-being.

The cited studies show that calorie restriction and fasting interventions in multiple studies were associated with improvements in mood and quality of life. This was especially seen in healthy adults and older populations.

The explanation is partly biological: during fasting the body temporarily switches to ketones as an energy source. These substances influence brain processes involved in neuroplasticity and mood, including through BDNF (brain-derived neurotrophic factor).

Important detail: the effects are usually modest and are mainly beneficial when combined with other lifestyle factors. In short, fasting is not an antidepressant, but it can have a supportive effect within a broader lifestyle.

Stress and the body: from stimulus to resilience

In the short term, fasting is a stressor. The body responds with increased cortisol levels and activation of the stress system. But here it becomes interesting: with repeated or controlled fasting periods, the system appears to adapt.

Studies show that longer or repeated fasting may lead to lower baseline cortisol levels and improved autonomic balance (greater parasympathetic activity).

This phenomenon is also called a “hormetic effect”: a small stressor ultimately makes the system stronger. In practical terms, this may translate into better stress regulation and a greater sense of mental resilience.

Meta-analytic evidence supports this view: fasting interventions are associated with improvements in perceived stress and emotional stability, although effect sizes vary widely between studies.

Cognition and focus: evolutionary sharpness

A commonly reported claim is that fasting improves mental clarity. Science partially supports this.

Under controlled conditions, improvements have indeed been found in executive functions such as attention and working memory.

The evolutionary explanation is plausible: in times of food scarcity, humans needed to remain alert to find food. Ketones also provide an efficient energy source for the brain.

Conclusion: expect mild cognitive benefits, but they depend strongly on duration, experience, and context.

Self-control and psychological meaning

An often underestimated effect of fasting is its impact on self-regulation and meaning-making.

Fasting requires suppressing impulses and maintaining a goal. Successfully completing a fasting period can therefore strengthen the sense of self-control. People report greater discipline and increased confidence in their ability to regulate behavior.

Context also plays a major role. Religious fasting periods are often associated with meaning, reflection, and emotional regulation.

This points to an important insight: the psychological benefits of fasting arise not only from biology but also from interpretation and intention; in short, from experience.

Individual differences: why one person thrives and another does not

Not everyone experiences fasting the same way. In fact, the variation is large.

Research shows that factors such as personality, emotional stability, and prior fasting experience play an important role. More experienced individuals report fewer negative emotions and less stress during fasting than beginners. So it is worth experimenting carefully.

It is also unsurprising that psychological traits matter. Individuals with better emotion regulation and lower impulsivity seem to experience more positive effects.

This highlights that fasting is not a “one size fits all” intervention. The effect strongly depends on who you are and how you apply it.

Paleo perspective

From an evolutionary perspective, prolonged fasting is seen as a recurring and normal condition in human history.

Early Homo sapiens lived in environments where food availability varied greatly due to seasonal changes, hunting success, and periods of drought. Food shortages were likely common, making the ability to function without food for extended periods a clear survival advantage.

In this context, metabolic flexibility developed: the body can switch from glucose metabolism to fat oxidation and ketone production when food is scarce. This mechanism, often referred to as “metabolic switching”, is considered an important adaptation that allowed both physical and cognitive functioning during scarcity.

From a paleo perspective, this metabolic flexibility was also likely accompanied by behavioral and cognitive adaptations. During fasting, humans had to actively search for food, requiring increased alertness, motivation, and efficient decision-making despite low energy availability. Some researchers argue that this evolutionary pressure helped preserve brain function under energy shortage conditions.

At the same time, it is noted that the modern environment differs strongly from this evolutionary reality: food is almost constantly available, and prolonged scarcity is rare.

As a result, fasting today can be seen both as a reactivation of ancient adaptive systems and as a stimulus that sometimes conflicts with modern lifestyle and physiological regulation. In a sense, it disrupts familiar patterns on multiple levels.

Summary

Prolonged fasting has measurable psychological effects. It may contribute to:

• slight improvement in mood
• better stress regulation
• increased mental focus
• stronger sense of self-control and meaning

However, these benefits depend on factors such as experience, context, and intention. It is not suitable for people with eating disorders, including those prone to muscle dysmorphia. When applied consciously and carefully, prolonged fasting can provide psychological benefits.

References

[1] Bonaccorsi, V., & Romeo, V. M. (2025). Psychological and psychiatric consequences of prolonged fasting: Neurobiological, clinical, and therapeutic perspectives. Nutrients, 18(1), 60. https://doi.org/10.3390/nu18010060

[2] Halson, S. L., et al. (2022). Fasting interventions for stress, anxiety and depressive symptoms: A systematic review and meta-analysis. Nutrients, 14(6), 1275