Two-Day Fasting Cycles Lowered Iron and Hemoglobin in Healthy Women: What the Research Shows

Two-Day Fasting Cycles Lowered Iron and Hemoglobin in Healthy Women: 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 know what repeated short fasting periods do to iron status in healthy, non-anemic women — a question that matters because women are already more prone to low iron than men due to menstrual blood loss. Rather than a single fast, the study used a repeated-cycle design: two groups of women each followed a different short fasting pattern, every 8 days, over a total of 48 days, while researchers tracked blood iron markers alongside mood and well-being. This connects to broader questions about how intermittent fasting affects the menstrual cycle and overall hormonal balance in women.

Who Was Studied

Participant profile: 46 healthy adult women, mean age approximately 25.5 years, with no diagnosed iron deficiency or anemia at baseline.

How the fasting protocol worked in this study: Each group abstained from food (water permitted) for either one or two consecutive days, repeated once every 8 days across a 48-day study period — effectively six fasting cycles per participant. Blood samples were taken to track iron-related markers before and after the repeated fasting cycles, alongside standardized questionnaires measuring mood and depressive symptoms.

What the Researchers Found

Iron status markers

• The two-day fasting cycles were consistently associated with the larger drop across nearly every iron parameter measured.
• Repeating short fasts every 8 days, six times over, was enough to move iron markers even in women who started with normal iron status.

Mood and well-being

• Both fasting patterns were associated with increased negative feelings and depressive symptom scores following the restriction periods, based on standardized mood questionnaires.
• The effect on mood appeared regardless of whether the group did one or two fasting days.

What Did Not Change

• Some iron management parameters beyond the core set (serum iron, ferritin, hemoglobin, hematocrit, RBC, TIBC) were not significantly affected by the shorter, one-day protocol, according to the study authors.

What the Researchers Concluded

The authors concluded that repeated short-term food restriction — particularly two consecutive fasting days — measurably lowers iron status markers in healthy women, and that these repeated fasting cycles also carry a mood cost, with both protocols linked to increased depressive feelings.

What This Means If You Fast

• Frequency and duration both matter. A single missed meal is very different from repeated multi-day fasting cycles — this study specifically tested people going without food entirely for one or two full days, repeated over time, not a typical 16:8 or 18:6 daily eating window.
• Menstruating women should pay closer attention to iron intake. If you already run close to the lower end of normal iron, layering frequent extended fasts on top of monthly blood loss is where deficiency symptoms are more likely to show up — see our guide on iron levels and intermittent fasting for women for practical steps.
• Mood dips during aggressive fasting cycles are a real, measured phenomenon, not just anecdotal — worth tracking alongside physical symptoms.
• This isn't a reason to avoid standard time-restricted eating. The protocol tested here (full 1–2 day fasts, repeated every 8 days) is far more aggressive than typical daily intermittent fasting windows, so these findings shouldn't be generalized to a standard 16:8 schedule without caution.
• If you fast for extended periods regularly, consider periodic bloodwork — ferritin and hemoglobin are inexpensive to check and can catch a downward trend before symptoms like fatigue or hair thinning appear.
• Iron-rich, high-bioavailability foods during your eating window matter more, not less, if you're doing longer or more frequent fasts.

Study Limitations

• Small sample size (46 total, 23 per group) limits how confidently the findings generalize.
• All-female sample means findings may not apply to men, and results here can't be generalized beyond premenopausal-age women.
• The fasting protocol tested (full 1–2 day food abstinence repeated every 8 days) is considerably more extreme than common intermittent fasting approaches like 16:8 or 5:2, limiting relevance to everyday fasters.
• No non-fasting control group was described in the summarized abstract, making it harder to separate the effect of repeated fasting from natural fluctuation over the 48-day study window.
• Full-text access was unavailable at the time of writing (PubMed and publisher pages returned 403 errors), so this summary relies on secondary, WebSearch-verified abstract and citation sources rather than the complete original dataset.
• Funding source and conflicts of interest were not identified in the available summaries.

Source

Wójciak, R. W. (2014). Effect of short-term food restriction on iron metabolism, relative well-being and depression symptoms in healthy women. Eating and Weight Disorders — Studies on Anorexia, Bulimia and Obesity, 19(3), 321–327. PMID: 24353086

Frequently Asked Questions

Does intermittent fasting cause iron deficiency in women?

Not typically with standard daily fasting windows. This study looked at a much more aggressive pattern — full 1- or 2-day fasts repeated every 8 days — and found that pattern significantly lowered iron markers in healthy women. A normal 16:8 eating window is a different exposure entirely.

How long do you have to fast before iron levels drop?

In this study, the effect was seen after repeated cycles of full-day fasting (one or two consecutive days), repeated six times over 48 days — not after a single missed meal or a daily time-restricted eating window.

Which iron markers are most affected by fasting?

The study found significant decreases in serum iron, hair iron, ferritin, hemoglobin, hematocrit, red blood cell count, and total iron-binding capacity in the group doing two consecutive fasting days.

Can fasting affect mood as well as iron levels?

Yes — both the one-day and two-day fasting groups in this study showed increased depressive symptom scores following the restriction cycles, independent of the iron findings.

Should women get bloodwork done if they fast frequently?

It's a reasonable precaution, especially for menstruating women doing longer or more frequent fasts. Periodic ferritin and hemoglobin checks can catch a downward trend before symptoms like fatigue, hair thinning, or brain fog appear.

Related Research and Articles

• Iron levels and intermittent fasting for women
• Does intermittent fasting deplete iron, zinc, and vitamin D?
• Intermittent fasting and the menstrual cycle
• Intermittent fasting and irregular periods
• Carb cravings before your period while fasting
• The best intermittent fasting schedule for women's weight loss

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