Side Effects of Intermittent Fasting in Women: What the Research Shows

Side Effects of Intermittent Fasting in Women: What the Research Shows

A 2021 clinical trial tested 16:8 time-restricted eating in 32 obese women over three months. The fasting group lost about four kilos. Body fat and waist size went down too. Blood tests linked to health risks did not get worse. The study did not report side effects like headaches or mood changes directly.

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 plan, especially if you have an existing health condition or take medication.

The Short Version

• What they tested: Whether eating only within an 8-hour window each day helps obese women lose weight without harming their health.
• Who did it: Juliana Dumke Schroder at the Federal University of Fronteira Sul, Brazil, published in the Journal of Translational Medicine in 2021.
• How many people: 32 obese women in total. All participants were women.
• How long: 3 months.
• What happened: Women who fasted lost about 4 kilos and showed no harmful changes in their blood tests.
• Read the study yourself: Journal of Translational Medicine 2021 →

What They Wanted to Find Out

Many women worry that fasting could harm their health, not just help their weight. This team wanted to see what really happens in the body during daily time-restricted eating. They picked obese women, a group often told to lose weight for health reasons. They measured body changes and blood tests, not just the scale.

This question matters because women's bodies can react differently to fasting than men's bodies do. Some research on iron levels during fasting has raised safety questions before. This study wanted real numbers, not guesses.

Who Was in the Study

Who they were: All 32 participants were women with obesity. Exact ages were not stated in the abstract.

What the fasting actually looked like: The fasting group had 16 hours with no food each day. They then ate normally during an 8-hour window. This is often called the 16:8 pattern. People were not assigned to a group by chance, so other factors could also explain some differences.

What Happened

The fasting group lost weight and body fat without any harmful changes in their blood tests.

• Body fat percentage went down in the fasting group.
• Waist size went down in the fasting group.
• A 30-year heart disease risk score dropped by about 12 percent in the fasting group.
• Blood tests tied to health risks like high blood sugar did not get worse.
• Quality of life was measured, but the specific scores were not stated in the abstract.

What Did Not Change

• Blood markers linked to health risks stayed stable — they did not worsen.
• The abstract does not report any muscle loss from fasting.
• No side effects such as headaches, dizziness or mood changes were reported in the abstract.

What the Researchers Said

The researchers said this fasting pattern lowered body weight without hurting the blood markers tied to common health risks. They said tracking body fat and muscle could help guide people using this kind of fasting.

What This Means for You

• If you are an obese woman considering fasting: this small study found weight loss with no reported harm to blood test results.
• If you are worried about hormones or nutrients: this study did not measure those directly, so it cannot answer that question for you.
• If muscle loss worries you: the abstract does not mention any muscle loss in the fasting group, though it was not the main focus.
• If you want proof of long-term safety: three months is too short to know what happens after a year or more.
• For women specifically: every single person in this study was a woman, which is rare — most fasting research uses mostly men. Still, this study alone cannot cover every possible side effect, like changes to iron and blood or low vitamin and mineral levels.
• If you notice hair changes while fasting: this study did not track that, but other research has looked at hair thinning.

What This Study Could Not Tell Us

• Only 32 women took part. That is a small number.
• It ran for 3 months, so it cannot say what happens after a year.
• People were not assigned to groups by chance, which makes the comparison less certain.
• Quality of life was measured, but it relies on what people reported themselves.
• The exact ages of the women were not stated in the abstract.
• Funding for the study was not stated in the abstract.

The Study Details

Schroder, J. D., Falqueto, H., Mânica, A., Zanini, D., de Oliveira, T., de Sá, C. A., et al. (2021). Effects of time-restricted feeding in weight loss, metabolic syndrome and cardiovascular risk in obese women. Journal of Translational Medicine. PMID: 33407612

Common Questions

Does intermittent fasting cause side effects in women?

This study of 32 obese women did not report side effects like headaches or dizziness. Blood tests tied to health risks did not get worse over 3 months. The study did not specifically ask women about symptoms, so smaller side effects may not have been captured.

How much weight did women lose with time-restricted eating in this study?

Women in the fasting group lost about 4 kilos over 3 months. They also lost body fat and reduced their waist size. The comparison group's weight change was not stated in the abstract.

Did time-restricted eating harm blood test results in women?

No. The study found no harmful changes in blood markers linked to common health risks. This was one of the main safety findings the researchers reported.

How long did the women fast each day in this study?

Women fasted for 16 hours each day. They ate all their food within an 8-hour window. This pattern is often called 16:8 fasting.

Is time-restricted eating safe for obese women?

In this small, 3-month study, it appeared safe for the women involved. But with only 32 people and a short time frame, it cannot prove safety for everyone or for longer periods.

More Research Like This

• Two-Day Fasting Cycles Lowered Iron and Hemoglobin in Healthy Women
• Does Intermittent Fasting Deplete Iron, Zinc, and Vitamin D?
• Intermittent Fasting Slowed Hair Regrowth by 18% in a Small Human Trial
• Time-Restricted Eating Does Not Reduce Bone Density in Seven Trials
• Seven-Day Water Fasting Pushes Healthy Adults Into Hypoglycemia 66% of the Time by Day 5
• Early Time-Restricted Eating Beats Later Eating for Fat Loss Without Costing Muscle
• Does Time-Restricted Eating Change Women's Hormones? No

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