Intermittent Fasting for Women: What the Evidence Shows

In 30 seconds

Intermittent fasting hasn’t been shown to work differently for women. In two small analyses of fasting trials, women lost similar amounts of weight before and after menopause. Evidence on hormones and periods is thin, perimenopause wasn’t studied, and pregnancy is not the time to fast to lose weight.

• In two small analyses, weight loss was similar before and after menopause, and matched men's in one.
• Both lasted 8 to 12 weeks and left out women in perimenopause.
• Fears that fasting upsets female hormones come largely from one study in very young rats.
• Don't fast to lose weight in pregnancy; if breastfeeding or with an eating disorder, talk to a professional first.

Does intermittent fasting work for women?

Do women respond to fasting differently from men? Two analyses from the same research group looked at this directly.

In a pooled analysis of three 12-week alternate-day fasting trials in adults with excess weight, weight fell by 4.6% in premenopausal women, 6.5% in postmenopausal women and 6.2% in men, with no significant difference between the groups.Source 11

In an 8-week trial of 4- or 6-hour eating windows, premenopausal and postmenopausal women with obesity both lost about 3.3% of their weight, with similar changes in fat mass, lean mass and insulin resistance.Source 22

Both analyses lasted 8 to 12 weeks, only included people with overweight or obesity and excluded women in perimenopause. The senior author of the alternate-day analysis consulted for the sponsor of that research.Source 11Source 22

Does fasting affect women’s hormones or periods?

Online warnings often cite animal research as if it showed what happens in women.

A review of human trials says worries that fasting disrupts female hormones and the menstrual cycle largely stem from one study in very young rats, which doesn't show how fasting affects adult women.Source 33

The human data are thin.

In the few small human trials it found, all in premenopausal women, the hormones that drive ovulation (LH and FSH) didn't change in one trial and prolactin didn't change in another, while androgen markers such as testosterone fell. It found no fasting trial that measured oestrogen, and the authors say firm conclusions aren't possible yet.Source 33

None of Blimbi’s sources shows how fasting affects your periods, and it’s unclear whether the hormone trials took blood on the same day of the cycle. If your periods change while you fast, raise it with a doctor.

Menopause and perimenopause

Both analyses found similar weight loss before and after menopause, but both left out perimenopause, so there’s no data here for that stage. None of Blimbi’s sources tested fasting for hot flushes or other menopause symptoms.

Age matters too. If you’re over 60, read intermittent fasting for older adults.

A National Institute on Aging overview says the long-term safety of fasting diets is uncertain and that trials typically enrolled adults aged 60 or younger.Source 44

Who shouldn’t fast?

Frequently asked questions

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• Who Should Not Do Intermittent Fasting Without Advice?

  Who should not do intermittent fasting without advice? Diabetes medicines, pregnancy and eating disorders need care; few data on children or over-60s.

• Intermittent Fasting for Older Adults: Is It Safe?

  Intermittent fasting for older adults: the US NIA says there is not enough evidence to recommend fasting diets. What to ask your clinician first.

• Water Fasting: What Trials Found and Who Should Avoid It

  Water fasting means only water, often for days. What small trials of 5- to 20-day fasts found, the lean mass loss two of them measured, and who shouldn't try it.

• Intermittent Fasting for Weight Loss: Realistic Results

  Intermittent fasting for weight loss shows modest average losses, about 4.6 kg more than control over 12 months, similar to daily calorie restriction.

• Alternate Day Fasting: How It Works and What Trials Found

  Alternate day fasting alternates fasting and eating days; it lost slightly more weight than other diets only in shorter trials. See who should ask first.

Frequently asked questions

Is intermittent fasting good for women?

It hasn't been shown to work differently for women: in two small analyses, weight loss was similar before and after menopause.Source 11Source 22

Can I fast on my period?

No source here studied fasting at different points of the cycle, so there's no evidence-based rule. The few hormone trials may not have standardised the day of the cycle.Source 33

Does intermittent fasting affect female hormones?

The evidence is thin: the review found no fasting trial in women that measured oestrogen, ovulation hormones didn't change in the one trial that checked, and the main fear comes from very young rats.Source 33

Is intermittent fasting OK during menopause?

There's little evidence. Two small analyses found similar weight loss before and after menopause, but they excluded perimenopause and didn't measure symptoms.Source 11Source 22

Sources

1. 1

   Does the weight loss efficacy of alternate day fasting differ according to sex and menopausal status?Shuhao Lin et al. Elsevier BV, February 1, 2021.DOI: 10.1016/j.numecd.2020.10.018 · PMID: 33358713Human randomized trial

2. 2

   Changes in body weight and metabolic risk during time restricted feeding in premenopausal versus postmenopausal womenSofia Cienfuegos et al. Elsevier BV, October 1, 2021.DOI: 10.1016/j.exger.2021.111545 · PMID: 34478825Human randomized trial

3. 3

   Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human TrialsSofia Cienfuegos et al. MDPI AG, June 3, 2022.DOI: 10.3390/nu14112343 · PMID: 35684143Narrative or mechanistic review

4. 4

   Calorie restriction and fasting diets: What do we know?National Institute on Aging. National Institute on Aging, August 14, 2018.Official guidance

5. 5

   Overview – Eating disordersNHS. NHS, January 23, 2024.Official guidance

6. 6

   Weight gain in pregnancyNHS. NHS, July 6, 2022.Official guidance

7. 7

   Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance