Fasting Improves Mood, Sleep, and Well-Being in 1,422 People: 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 wanted to understand what actually happens to people's mood, sleep, energy, and physical wellbeing during medically supervised extended fasting — using daily measurements across a large group. Most prior studies on fasting and subjective wellbeing had used small samples or short timeframes. This study tracked over 1,400 adults across fasting periods of 4–21 days, asking a simple question: does prolonged fasting make people feel better or worse, and which specific dimensions change? For context on the mechanisms involved, see our article on what happens to your body during intermittent fasting and how intermittent fasting affects the brain.

Who Was Studied

Participant profile: Adults attending the Clinica Buchinger Wilhelmi, ranging broadly in age and health status. Participants included people with chronic conditions (metabolic syndrome, musculoskeletal disorders) as well as healthy individuals seeking preventive health care.

How the Buchinger fasting protocol worked in this study: Participants consumed no solid food and limited caloric intake to approximately 200–250 kcal per day from vegetable broth, herbal teas, and small amounts of diluted fruit juice. They engaged in daily light exercise (walking), relaxation practices, and received regular medical monitoring. This is a more structured and calorically minimal form of fasting than typical intermittent fasting protocols.

What the Researchers Found

Subjective Well-Being

Participants rated their physical and emotional wellbeing daily on validated scales. Both dimensions improved progressively from the first day of fasting:

Key findings:

• The vast majority of participants reported improved general wellbeing by the end of the fasting period — improvements in both physical and emotional dimensions were statistically significant
• Sleep quality improved from the very first day of fasting — one of the most consistent and early-onset findings in the study
• Hunger was low and continued declining after the first day — contrary to the common assumption that extended fasting would produce escalating hunger
• Mood enhancement was particularly notable from around day 4, consistent with the timeframe in which the body typically completes the metabolic transition into ketosis

Adverse Events

Most adverse events occurred in the first 1–2 days of fasting and resolved spontaneously. The overall safety profile was described by the authors as favourable.

Physical Health Outcomes

• Body weight decreased at a consistent rate throughout the fasting period
• Blood pressure decreased significantly in participants with elevated baseline levels
• Reports of musculoskeletal pain and other chronic symptoms improved progressively

What Did Not Change

• No significant increase in anxiety or negative mood states at the group level
• No deterioration in cognitive function during fasting
• No muscle-related concerns at the supervised intensity level with light daily exercise

What the Researchers Concluded

The authors concluded that medically supervised prolonged fasting is safe in a large, mixed-health-status population and that it consistently produces improvements in subjective wellbeing across physical, emotional, and sleep dimensions. They noted that the progressive improvement in mood and wellbeing across the fasting period, combined with the rapid decline in hunger after day one, challenges the assumption that extended fasting is a predominantly negative experience.

What This Means If You Fast

• The "suffering" narrative about fasting isn't supported by data. In this study of over 1,400 people, wellbeing improved, sleep quality improved, and hunger subsided quickly — even in fasts lasting up to three weeks. Most people's fears about fasting are worse than the actual experience.
• Sleep improvements appear quickly. This study found sleep quality improved from day 1 of the fast — consistent with the explanation that reducing late-evening insulin and gut activity allows sleep to deepen. If your sleep has been poor, addressing your eating window timing may be more impactful than you expect.
• Mood takes a few days to improve. The most pronounced emotional wellbeing gains appeared from around day 4 — consistent with the timeline for entering stable ketosis. For shorter intermittent fasting protocols (16:8, 18:6), this mechanism is compressed but the same principle applies: the mood benefits become clearer after metabolic adaptation.
• Hunger resolves faster than expected. One of the most striking findings is that hunger was already low by day 1 and continued declining. This is consistent with what practitioners of OMAD and extended fasting consistently report: genuine hunger resolves quickly once the transition is complete.
• The safety profile is reassuring. Adverse events were mild, mostly confined to the first 48 hours, and none were serious. Headache, weakness, and dizziness in the first days of fasting are common and transient — typically resolved by electrolyte management.
• The wellbeing improvements were broad. Both physical and emotional dimensions improved, and chronic pain and musculoskeletal symptoms also improved. This multi-dimensional improvement is consistent with fasting's effects on systemic inflammation.

Study Limitations

• No control group: As a prospective observational study, there was no matched group not fasting. Reported wellbeing improvements could partly reflect expectation effects, the relaxing clinic environment, supervised care, or the structured daily exercise — not fasting alone.
• Specialised setting: All participants fasted at a dedicated clinic with medical supervision and daily monitoring. Results may not directly transfer to unsupervised home fasting.
• Self-reported outcomes: Wellbeing and sleep quality were based on participant self-report rather than objective measures (polysomnography for sleep, validated biomarkers for mood).
• No long-term follow-up: The study measured wellbeing during the fast, not sustained changes at 3 or 6 months post-fast.
• Participant selection: People who voluntarily attend a fasting clinic are likely highly motivated and positively predisposed to fasting — which could inflate reported wellbeing improvements versus a general population sample.
• Caloric restriction vs. strict fasting: The Buchinger protocol (200–250 kcal/day) is not identical to strict water fasting or standard intermittent fasting, and differences in outcomes between these approaches cannot be determined from this study.

Source

Wilhelmi de Toledo F, Grundler F, Bergouignan A, Drinda S, Michalsen A. (2019). Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLOS ONE, 14(1): e0209353. PMID: 30601864

Frequently Asked Questions

What exactly is Buchinger fasting?

Buchinger fasting is a medically supervised form of prolonged fasting developed at the Clinica Buchinger Wilhelmi in Germany. Participants consume approximately 200–250 kcal per day from vegetable broth, herbal teas, and diluted juices — essentially no solid food. It is accompanied by light exercise, relaxation, and regular medical monitoring. It is more intensive and longer than standard intermittent fasting but shares the same core principle of giving the digestive system an extended rest.

Did participants actually feel well during a multi-week fast?

Yes — and this surprised many readers of the study. By around day 4, emotional wellbeing scores had improved significantly from baseline and continued improving. The pattern observed — initial mild difficulty in the first 1–2 days followed by progressive wellbeing improvement — is consistent with the metabolic transition into ketosis, during which the brain shifts from glucose to ketones as its primary fuel.

Why would sleep improve from day 1 of fasting?

Sleep quality improved from the very first day, which suggests the mechanism does not depend on full ketosis or extended fat adaptation. The most likely explanation is a rapid reduction in late-evening insulin levels and the quieting of gut activity overnight — both of which allow the hormonal cascade supporting deep sleep to function without disruption. Eating less food, and none late at night, removes interference from sleep architecture almost immediately.

Can these results be expected with everyday intermittent fasting (16:8, OMAD)?

The Buchinger protocol is more intensive than standard 16:8, but the underlying mechanisms are shared. Clinical and community data from standard intermittent fasting consistently shows similar directional improvements in mood, sleep, and wellbeing — typically appearing over weeks rather than days, in line with the slower metabolic adaptation of shorter fasting windows.

How significant were the adverse events?

Mild and mostly confined to the first 48 hours. Headache (8.4%), weakness (7.9%), and dizziness (6.8%) were the most common. These resolve spontaneously for most people and are largely attributable to electrolyte shifts and the body's initial adjustment to switching fuel sources. No serious adverse events were reported across 1,422 participants.

Related Research and Articles

• Intermittent fasting and brain health: the neuroscience
• Does intermittent fasting affect sleep?
• Intermittent fasting and inflammation: the research explained
• What happens to your body during intermittent fasting?
• Electrolytes and intermittent fasting
• Intermittent fasting and longevity: what the science says
• How intermittent fasting promotes autophagy

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