Time-Restricted Eating Improved Periods in 7 of 10 Women With PCOS: What the Research Shows

Time-Restricted Eating Improved Periods in 7 of 10 Women With PCOS: What the Research Shows

Researchers tested an 8-hour eating window in 18 women with PCOS and irregular periods. After 5 weeks, 11 of 15 women who finished the study saw their periods become more regular. The study did not test fasting on period days themselves, but it shows time-restricted eating can help some women's cycles.

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.

The Short Version

• What they tested: Eating only within an 8-hour window each day, to see if it helps irregular periods in PCOS.
• Who did it: Li C (first author) at Shengjing Hospital of China Medical University, published in the Journal of Translational Medicine in 2021.
• How many people: 18 women signed up, all of them women, ages 18 to 31.
• How long: 6 weeks in total — 1 week eating normally, then 5 weeks of the 8-hour eating window.
• What happened: 11 of the 15 women who finished saw their periods become more regular.
• Read the study yourself: Journal of Translational Medicine 2021 →

What They Wanted to Find Out

Many women search for ways to fast without upsetting their period. This study did not test fasting on period days. Instead, it asked a bigger question: can a shorter eating window fix irregular periods?

The women in this study had PCOS, short for polycystic ovary syndrome. This is a hormone condition that often stops ovulation — the release of an egg each month. Researchers wanted to know if eating only within 8 hours a day could bring periods back on track. For more on fasting and this condition, see how time-restricted eating affected PCOS ovulation and whether fasting improves PCOS hormones.

Who Was in the Study

Who they were: All 18 women had PCOS and were not ovulating regularly. They were between 18 and 31 years old. The abstract does not say their weight category.

What the fasting actually looked like: For 5 weeks, the women ate all their food between set hours, leaving an 8-hour window open each day. Outside that window, the abstract does not say if they could drink water or calorie-free drinks. Before the fasting period, they had one week of eating as usual, to measure their starting point.

What Happened

Most women's periods became more regular after eating only within an 8-hour window.

• Body weight and body fat went down. Exact amounts are not stated in the abstract.
• A male hormone linked to PCOS (testosterone) went down.
• A hormone that carries sex hormones in the blood (SHBG) went up.
• The body handled insulin better, based on a standard blood test.
• A blood test for inflammation in the body also improved.

What Did Not Change

• The researchers also measured muscle mass. It was not listed as one of the things that changed. This suggests the women likely did not lose muscle, though the study does not say so directly.
• Fasting blood sugar and cholesterol-type measurements (lipids) were tracked too. They were not listed as changing either.
• Two hormones that control ovulation (LH and FSH) were measured. The study does not say these changed on their own.

What the Researchers Said

The researchers concluded that eating within 8 hours a day may help women with PCOS who are not ovulating. They said it can lower body fat, improve periods, and ease signs of excess male hormones and inflammation.

What This Means for You

• If you have PCOS: This study suggests a shorter eating window might help your periods. Talk to your doctor before you try it.
• If your periods are already regular: This study was done in women with irregular cycles, so it may not apply to you the same way.
• For women specifically: All 18 participants were women. The study was small, so it cannot say this works for every woman with PCOS.
• On fasting during your period itself: This study did not test eating patterns during the days you are bleeding. It only tracked whether cycles became regular over time.
• Start slowly: An 8-hour window is a big change from normal eating. Many women build up to it over a few weeks.
• Check related research: See how fasting affected menstrual regularity in PCOS and whether time-restricted eating changes women's hormones.

What This Study Could Not Tell Us

• Only 18 women joined, and just 15 finished — a small group of people.
• It only looked at women with PCOS, so we don't know if it applies to women without PCOS.
• All participants were women, but the study did not have a separate comparison group.
• It lasted just 6 weeks, so it cannot say what happens after fasting for a year.
• Women tracked their own periods, which depends on accurate reporting.
• The abstract does not say who paid for this research.

The Study Details

Li, C., Xing, C., Zhang, J., Zhao, H., Shi, W., & He, B. (2021). Eight-hour time-restricted feeding improves endocrine and metabolic profiles in women with anovulatory polycystic ovary syndrome. Journal of Translational Medicine. PMID: 33849562

Common Questions

Can I keep fasting during my period?

This study did not test fasting on period days themselves. It tested an 8-hour eating window over several weeks, not single days. Talk to your doctor if fasting during your period feels harder than usual.

Does intermittent fasting affect your menstrual cycle?

In this study of women with PCOS, 11 of 15 women had more regular periods after 5 weeks of an 8-hour eating window. This does not prove fasting fixes every period problem. It was tested only in women with PCOS.

Can intermittent fasting make periods more regular?

In this small study, about 7 in 10 women saw their periods become more regular. All of them had PCOS and irregular cycles before starting. It is not known if this works the same way for other women.

Does water fasting affect periods?

This study tested time-restricted eating, not water-only fasting. The abstract does not mention water fasting at all. We cannot say from this study what water fasting does to periods.

Should I fast according to my menstrual cycle?

This study did not test changing the fasting schedule around the cycle. It used the same 8-hour window every day for 5 weeks. The abstract does not say if timing fasting around the cycle changes results.

More Research Like This

• Time-restricted eating improved insulin and hormones in PCOS
• 5:2 fasting improved menstrual regularity in women with PCOS
• Intermittent fasting and hormone profiles in PCOS
• Time-restricted eating helped women with PCOS lose weight
• Does time-restricted eating change women's hormones?
• Two-day fasting cycles and iron levels in women
• Intermittent fasting and ovarian reserve in women

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