Prolonged Daily Fasting Did Not Worsen Dry Eye Symptoms in a 2025 Study: What the Research Shows

Prolonged Daily Fasting Did Not Worsen Dry Eye Symptoms in a 2025 Study: 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

A persistent concern among people who fast for long daily stretches — including many who follow 16:8 or longer time-restricted eating windows — is whether going long hours without fluids dries out the eyes. Researchers set out to test this directly, comparing objective, instrument-measured tear film quality and subjective dryness symptoms during fasting periods versus non-fasting periods in the same group of people. You can read more about why drinking water is one of the most important rules of fasting and how to manage electrolytes during a fasting window in related articles on this site.

Who Was Studied

Participant profile: All 40 participants were assessed at two timepoints — during an active fasting period and during a non-fasting period — allowing each person to serve as their own comparison. Full demographic breakdowns (age range, sex split) were not available in the public summary of the study.

How the fasting protocol worked in this study: Participants fasted for at least 12 hours per day, including complete abstinence from both food and fluids during fasting hours, for a minimum of two weeks. This is comparable in structure to an extended time-restricted eating window, though undertaken as religious observance rather than a lab-designed weight-loss or metabolic protocol.

What the Researchers Found

Tear Film and Dry Eye Measures

Researchers used the Oculus Keratograph 5M, an instrument that objectively measures tear film stability and volume, alongside a standard patient-reported dryness questionnaire (Ocular Surface Disease Index, OSDI).

• Tear film stability (NIKBUT) was numerically better, not worse, during fasting periods — though the researchers reported this difference did not reach statistical significance
• No significant difference was found in tear volume or patient-reported dryness symptoms between fasting and non-fasting periods
• Patients used significantly fewer lubricating eye drops during fasting periods than during non-fasting periods

What Did Not Change

• Objective tear film break-up time did not worsen with fasting
• Tear meniscus height (a marker of tear volume) showed no significant change
• Subjective dryness symptom scores (OSDI) showed no significant change

What the Researchers Concluded

The study authors concluded that prolonged fasting — including complete abstinence from fluid intake during fasting hours — did not lead to significant ocular dryness, either objectively or subjectively, in this cohort.

What This Means If You Fast

• Long fasting windows are unlikely to meaningfully dry out your eyes. This study directly tested the concern and found no significant worsening of tear film quality or dryness symptoms during prolonged daily fasting.
• Reduced eye drop use during fasting is a useful data point. Participants needed fewer lubricating drops while fasting, suggesting no increase — and possibly even a slight easing — in dryness symptoms.
• Hydration during your eating window still matters. This study does not mean fluid intake is irrelevant — it suggests the body appears to compensate reasonably well for the fasting hours themselves. See our guide on why drinking water is the most important rule of fasting for practical hydration timing.
• If you already have dry eye disease, individual results may differ. This cohort's baseline eye health wasn't detailed in the available summary, so people with pre-existing significant dry eye conditions should still monitor their symptoms and consult an eye care professional if fasting coincides with worsening symptoms.
• This adds to a broader pattern in fasting research: many commonly feared side effects of extended fasting windows (like this one) turn out to be smaller in controlled measurement than anecdote suggests.

Study Limitations

• Small sample size — 40 participants is enough to detect a large effect but may miss more subtle changes
• Detailed demographic data (age range, sex distribution) was not available in the public study summary used for this article
• Observational, within-subject design, not a randomized controlled trial — participants were not randomly assigned to fast or not fast
• Religious/cultural fasting context — findings come from prolonged daily religious fasting rather than a fasting protocol designed specifically for weight loss or metabolic research, which may affect how directly the results generalise to all time-restricted eating approaches
• A confirmed PubMed PMID for this study could not be located at the time of writing — this article cites the PubMed Central (PMC) record instead

Source

Alomari AF, Issa S, Musleh A, Abusamak M, Bdair O, AlRyalat SA, Al-Wakfi A, Jaber M, Alloubani A, Sahawneh H, El-Faouri M, Abdul Aziz A, Al Bdour M. (2025). Impact of religious fasting on ocular dryness: objective and subjective assessment. Frontiers in Medicine. View on PubMed Central →

Frequently Asked Questions

Does intermittent fasting cause dry eyes?

This 2025 study found no significant increase in dry eye symptoms or tear film instability during prolonged daily fasting compared to non-fasting periods, even when fasting included complete abstinence from fluids. Tear film stability was actually numerically slightly better during fasting, though not statistically significant.

Should I drink water during my eating window to protect my eyes while fasting?

Yes — general hydration is still important for eye health and overall wellbeing. This study suggests the body handles the fasting hours themselves reasonably well, but it doesn't mean hydration during your eating window stops mattering.

Did people in the study need more eye drops while fasting?

No — the opposite was found. Participants used significantly fewer lubricating eye drops during fasting periods than during non-fasting periods.

Is this the same as time-restricted eating (16:8, 18:6, etc.)?

Not exactly. Participants in this study fasted for religious reasons for at least 12 hours a day over a minimum of two weeks, including abstaining from fluids. This is structurally similar to an extended time-restricted eating window but was not designed as a weight-loss or metabolic health protocol.

What should I do if my eyes feel dry while intermittent fasting?

If you notice dry eye symptoms while fasting, don't assume fasting itself is the cause without ruling out other factors — screen time, air conditioning, sleep quality, and allergies are common contributors. If symptoms persist or worsen, consult an eye care professional rather than self-diagnosing.

Related Research and Articles

• Why drinking water is the most important rule of fasting
• Do electrolytes break a fast?
• Electrolytes and intermittent fasting
• Intermittent fasting in summer heat: staying hydrated
• Research: Fasting-mimicking diet improves skin hydration

Want the complete guide to fasting? Get Intermittent Fasting in Practice on Amazon — and claim 3 months free on our fasting app at fastinginpractice.com/redeem.