Fasting Reduces Anxiety and Depressive Symptoms Without Increasing Fatigue: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Researchers at Aix-Marseille University wanted to answer a question that millions of people who fast have wondered about: does restricting when or how much you eat affect your mood, anxiety, or stress levels — and if so, in which direction? This meta-analysis pulled together 11 controlled studies involving 1,436 participants to produce a pooled statistical answer. It also examined whether fasting was associated with increased fatigue — a common concern raised by critics of fasting protocols. Interested in how fasting affects the brain more broadly? See our articles on intermittent fasting and brain health and does fasting improve brain function and focus?

Who Was Studied

Participant profile: The included studies covered a range of adults across different ages, health statuses (including participants with type 2 diabetes), and countries. Fasting types included intermittent fasting protocols (daily time-restricted eating, 5:2 fasting), Ramadan-style fasting, and longer structured fasting interventions.

Important methodological note: The primary meta-analytic findings cited below were drawn from the subset of studies identified as randomised controlled trials (RCTs) with low risk of bias — the most methodologically rigorous subgroup within the full review. This distinction matters: the effect of fasting on mood was clearest when the studies were of highest quality.

What the Researchers Found

Anxiety Symptoms

• Fasting produced a statistically significant reduction in anxiety symptoms compared to control groups (b = −0.508, p = 0.038) when analyses were limited to RCTs with low risk of bias.
• The effect was consistent across different fasting types included in the high-quality subset.

Depressive Symptoms

• Fasting produced a statistically significant reduction in depressive symptoms compared to controls (b = −0.281, p = 0.012) in the low-risk-of-bias RCT subset.
• The depression effect was somewhat smaller in magnitude than the anxiety effect but remained statistically robust.

Fatigue and Energy

• Fasting did not increase fatigue — a common clinical concern that the data did not support.
• The researchers found no significant increase in fatigue in fasting groups compared to controls.
• This finding directly challenges the assumption that restricting eating leads to energy depletion affecting mood.

BMI and Body Weight

• Fasting groups had lower BMI compared to control groups, which was an expected secondary finding.
• The reduction in body weight associated with fasting may have contributed to mood improvements via reduced inflammation, improved metabolic markers, and enhanced self-efficacy — though the meta-analysis did not test these mediating pathways directly.

What Did Not Change

• No significant increase in fatigue — the most important null finding in this study for practical fasters
• No statistically significant harm signals even in participants with type 2 diabetes

Safety Note

The researchers specifically examined safety in metabolically vulnerable populations. Fasting interventions were found to be safe even in patients with type 2 diabetes — though this does not eliminate the need for medical supervision in that population.

What the Researchers Concluded

The authors concluded that fasting interventions are associated with significantly lower anxiety and depression levels compared to control conditions in RCTs with low risk of bias, without increasing fatigue. They noted that the available evidence has limitations (heterogeneity of fasting protocols, variation in outcome measures, relatively small individual study sizes) but that the overall signal is sufficiently consistent to warrant further high-quality investigation, particularly dedicated RCTs with standardised fasting protocols and validated psychiatric outcome measures.

What This Means If You Fast

• Anxiety may genuinely improve with fasting. The statistically significant reduction in anxiety across multiple studies suggests this is a real biological effect, not placebo. Mechanisms likely include lower inflammatory cytokines, stabilised blood sugar (which reduces cortisol-driven anxiety), and increased BDNF production.
• Fasting is unlikely to worsen your mood. The absence of a fatigue increase is important — it means the energy restriction inherent in fasting does not appear to translate into worsened mental state in most people. Learn how fasting boosts brain-derived neurotrophic factor (BDNF).
• The first week is the exception. The studies in this meta-analysis covered established fasting participants, not people in the difficult initial adaptation period. The first 7–10 days of fasting can involve mood fluctuations — irritability, low energy, difficulty concentrating — before the improvements set in.
• Depression effects are real but modest. The effect size for depression (b = −0.281) is smaller than for anxiety (b = −0.508). Fasting should not be positioned as a replacement for treatment of clinical depression, but it may be a useful complementary strategy.
• Blood sugar stability is the likely mechanism. Many mental health improvements linked to fasting track closely with improved insulin sensitivity and blood sugar regulation — both of which reduce the hormonal stress signalling that drives mood instability. Read more about fasting and inflammation research.

Study Limitations

• Heterogeneity of fasting protocols: The included studies used different fasting types (IF, Ramadan, prolonged fasting), making it difficult to attribute effects to one specific protocol.
• Variation in outcome measures: Different studies used different validated scales for anxiety and depression (PHQ-9, BDI, HADS, etc.) — the meta-analysis had to standardise across these.
• Publication bias: While the authors reported no statistically significant publication bias, this is always a concern with meta-analyses.
• Limited long-term data: Most included studies were short-duration; the sustained effect of fasting on mood over 12+ months is less well-characterised.
• Population variability: Studies included healthy adults, people with metabolic conditions, and people undergoing Ramadan — generalising to any single population requires caution.
• Sex and age breakdown: The meta-analysis does not appear to have had sufficient data to stratify findings by sex — an important gap given known differences in how fasting affects women and men hormonally.
• No active control for diet quality: Some improvements may partly reflect better overall nutrition choices that accompany structured fasting regimens.

Source

Berthelot E, Etchecopar-Etchart D, Thellier D, Lancon C, Boyer L, Fond G. (2021). Fasting Interventions for Stress, Anxiety and Depressive Symptoms: A Systematic Review and Meta-Analysis. Nutrients, 13(11), 3947. PMID: 34836202

Frequently Asked Questions

Does intermittent fasting help with anxiety?

Based on this 2021 meta-analysis of 11 studies and 1,436 participants, yes — fasting was associated with significantly lower anxiety compared to controls (b = −0.508, p = 0.038) when analysis was restricted to low-risk-of-bias RCTs. The effect was consistent across different fasting types.

Does intermittent fasting help with depression?

The meta-analysis found a statistically significant reduction in depressive symptoms in fasting groups compared to controls (b = −0.281, p = 0.012). The effect is real but modest, and fasting should be considered a supportive tool rather than a standalone treatment for clinical depression.

Will fasting make me tired or low energy?

This meta-analysis specifically examined fatigue outcomes and found that fasting did NOT significantly increase fatigue compared to control conditions. This finding held even in participants with type 2 diabetes. That said, the initial adaptation period (first 7–14 days) can involve temporary energy fluctuations before the body adapts to fat burning.

How does fasting improve mood — what's the mechanism?

Researchers propose several overlapping mechanisms: reduced neuroinflammation (lower CRP, IL-6), improved neuronal insulin sensitivity, increased production of BDNF (brain-derived neurotrophic factor which supports mood regulation), stabilised blood sugar (reducing cortisol-driven anxiety), and the psychological benefits of improved metabolic control and body composition.

Is fasting safe for people with anxiety or depression who are on medication?

This meta-analysis found fasting to be safe even in patients with type 2 diabetes. However, psychiatric medication — particularly antidepressants and anxiolytics — can interact with fasting via changes in absorption timing, blood sugar effects, and pharmacokinetics. Anyone on psychiatric medication should consult their prescribing doctor before starting a fasting protocol.

Related Research and Articles

• Intermittent fasting and brain health: the neuroscience
• Intermittent fasting and inflammation: the research explained
• Does fasting improve brain function and focus?
• Intermittent fasting and longevity: what the science says
• What happens to your body hour by hour when you fast

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