16:8 Intermittent Fasting Significantly Improves Quality of Life and Reduces 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 the University Medical Center of Mainz wanted to understand whether a standard 16:8 intermittent fasting protocol — 16 hours of fasting per day, at least 5 days per week — could meaningfully improve quality of life and reduce fatigue in healthy adults over a three-month period. Rather than studying metabolic disease or weight loss as the primary outcome, this study placed quality of life, fatigue, and safety at the centre — outcomes that matter to everyday people deciding whether fasting is worth doing. If you're interested in what fasting does to your energy and sense of wellbeing, rather than just your waistline, this study speaks directly to that question.

Related reading: What happens to your body hour by hour when you fast and Intermittent fasting benefits: the complete science-backed guide.

Who Was Studied

Note: This was a single-arm prospective cohort study — all participants followed the fasting protocol. There was no separate control group. Results represent within-participant changes from baseline to 3 months.

Participant profile: Healthy adult volunteers without significant chronic disease, recruited through the University Medical Center of Mainz. Participants maintained their normal lifestyle, including diet and physical activity, with the only intervention being the 16-hour daily fasting window.

How 16:8 worked in this study: Participants fasted for 16 consecutive hours each day (including overnight sleep) and restricted all eating to an 8-hour window. The specific timing of the eating window was not fixed — participants chose a window that suited their schedule. The protocol required adherence for at least 5 of 7 days per week over the full 3-month study period.

What the Researchers Found

Quality of Life (SF-36 and WHO-5)

Quality of life was assessed using two validated questionnaires: the Short Form-36 (SF-36), which measures physical and mental health across eight domains, and the WHO-5 Well-Being Index. Both improved significantly over the 3-month fasting period, with participants reporting better overall health status, energy levels, and emotional wellbeing compared to their baseline measurements.

Fatigue (FAS and FSS)

Fatigue was measured with two scales: the Fatigue Assessment Scale (FAS) and the Fatigue Severity Scale (FSS). Both showed significant reductions over the three months.

Key findings:

• Mental fatigue fell by nearly 2 points on the FAS scale — a clinically meaningful reduction achieved without any additional intervention beyond fasting
• Total fatigue burden also fell significantly, with p-values of 0.002 indicating strong statistical confidence
• Fatigue reductions were observed at both intermediate time points (short-term) and at the 3-month mark (long-term), suggesting the benefit was not merely a novelty effect

Body Weight

Participants lost body weight over the three-month period, consistent with findings in other intermittent fasting studies. The study was not designed primarily as a weight-loss trial, and the focus was on quality of life outcomes, but the weight reduction was noted as an additional benefit.

What Did Not Change

• Laboratory safety parameters: No clinically significant changes were detected in blood tests. The researchers concluded that 16:8 fasting maintained a good safety profile with no adverse effects on key metabolic or haematological markers.
• Adverse events: No participants reported serious adverse events attributable to the fasting protocol.

What the Researchers Concluded

The authors concluded that 16:8 intermittent fasting practiced for three months significantly improved several aspects of quality of life and reduced fatigue in healthy adults, while maintaining a good safety profile. The combination of improved wellbeing and reduced fatigue — without calorie counting, special foods, or structured exercise — positions intermittent fasting as an accessible and practical health behaviour for the general population.

What This Means If You Fast

• Fatigue reduction is a documented benefit, not just anecdote. The statistically significant falls in both mental and total fatigue scores confirm what many people report subjectively: that fasting makes them feel less tired and more mentally clear after the initial adaptation period.
• Quality of life improves over time, not just acutely. The 3-month design showed that benefits persisted and grew over time, suggesting that the adaptation phase (often the first 1–2 weeks) leads to longer-term gains.
• 16:8 appears safe for healthy adults. No clinically significant lab changes were observed. This supports the broader body of evidence that standard intermittent fasting does not carry hidden metabolic risks for otherwise healthy people.
• The fasting window timing is flexible. Participants were allowed to choose their own 8-hour eating window. This suggests you don't need a specific window (e.g., noon–8pm) to see benefits — the consistent 16-hour fasting duration is what matters.
• You need at least 3 months to see the full picture. Short-term discomfort in weeks 1–2 gives way to meaningful fatigue reduction and quality of life improvement by 3 months. Persistence through the early adjustment phase is key. Read more about how to get through the first 10 days of intermittent fasting.
• Fasting doesn't require calorie restriction to improve wellbeing. Participants maintained their normal diet and lifestyle. The fasting window alone drove the quality of life improvements.

Study Limitations

• No control group. Without a randomised control arm, it is not possible to rule out placebo effects, seasonal changes, or natural fluctuation in quality of life over time. Participants knew they were fasting, which may have influenced self-reported wellbeing.
• Small sample size (n=30). The study population was small, limiting statistical power and generalisability. Larger trials are needed to confirm these findings across diverse populations.
• Healthy volunteers only. Results may not apply directly to people with chronic illness, obesity, or metabolic conditions.
• Self-reported outcomes. Quality of life and fatigue scores rely on participant self-assessment, which is inherently subjective.
• No long-term follow-up. The 3-month endpoint does not tell us whether improvements are maintained if fasting is discontinued or continued beyond the study period.
• Institution and recruitment bias. Participants were recruited from a single German university medical centre, which may not represent the general population.

Source

Anic, K., et al. (2022). Intermittent Fasting—Short- and Long-Term Quality of Life, Fatigue, and Safety in Healthy Volunteers: A Prospective, Clinical Trial. Nutrients, 14(19), 4216. PMID: 36235868

Frequently Asked Questions

Does intermittent fasting make you feel better?

This study found that 16:8 fasting significantly improved quality of life scores on both the SF-36 and the WHO-5 Well-Being Index over 3 months. Participants also reported meaningful reductions in fatigue. The benefits grew over time rather than fading, which suggests adaptation plays a key role.

How long does it take for intermittent fasting to improve energy levels?

Based on this study's design, participants experienced significant fatigue reductions over the 3-month period. Many people report the most difficult adjustment in the first 1–2 weeks, with improvements in energy and mental clarity becoming noticeable after the body adapts to fat-burning as a primary fuel source.

Is 16:8 intermittent fasting safe for healthy adults?

This study found no clinically significant changes in laboratory parameters (blood tests) over 3 months of 16:8 fasting in healthy volunteers, supporting a good safety profile for this protocol. This is consistent with the broader research literature on intermittent fasting in healthy populations.

What does the FAS score measure and what is a meaningful change?

The Fatigue Assessment Scale (FAS) measures both physical and mental fatigue. Lower scores indicate less fatigue. In this study, mental fatigue fell from 10.3 to 8.4 (a reduction of nearly 2 points) with high statistical significance (p=0.002), representing a clinically meaningful improvement in how tired and mentally drained participants felt day-to-day.

Can I choose my own eating window on 16:8?

Yes — this study allowed participants to choose their own 8-hour eating window based on their schedules. The findings suggest that the consistent 16-hour fasting duration, regardless of which specific hours you eat, is what drives the wellbeing benefits.

Related Research and Articles

• Intermittent fasting benefits: the complete science-backed guide
• Intermittent fasting and brain health: the neuroscience
• Does intermittent fasting improve brain function and focus?
• Intermittent fasting and inflammation: the research explained
• How to get through the first 10 days of intermittent fasting

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