Is intermittent fasting safe for women?

For many healthy adult women a moderate schedule such as 12:12 to 16:8 is a reasonable thing to try. In pregnancy, while breastfeeding or under 18, fast only on medical advice. With a current or past eating disorder, we advise against it; talking to a doctor is the better start. Periods that become irregular or stop are a sign to ease off.

Can I do intermittent fasting during my period?

No official guidance says you can't. Our cycle planner suggests a gentler 12:12 to 14:10 window while you are bleeding, because energy is often lower then. That suggestion is our own framework, and the research on fasting by cycle phase is very limited.

How many hours should a woman fast?

There is no official number for women. Common daily schedules run from 12 to 16 hours of fasting, and a gentle start is 12 hours overnight. Anything beyond a full day without food needs a doctor's advice first.

Intermittent Fasting for Women: Trials, Cycle and Age

Q: What is the best intermittent fasting schedule for women over 50?

No trial shows one schedule is best after 50. Pick a moderate window that leaves room to eat enough protein. From 65, that means at least 1.0 to 1.2 g for each kilogram you weigh every day. If you are active, it means 1.2 g or more.

Intermittent fasting for women works the same basic way it does for anyone. Fixed eating hours make it easier for some people to eat less, and trials in women found weight loss similar to ordinary calorie cutting. What differs for women is the menstrual cycle, which responds to how much energy you take in, and the changes that come with age.

What trials in women have found

One trial of intermittent fasting in women alone was published in 2011. It followed 107 women for 6 months. One group ate about 2,710 kJ (about 650 calories) on two days a week and normally on the rest. The other group cut calories a little every day.

Trial	Who took part	What was tested	Result
2011, 6 months	107 women	Two low-calorie days a week against a daily calorie cut	The same weight loss in both groups
2022, 12 months	139 adults with obesity	Eating within 8 hours with a calorie cut, against the same calorie cut alone	8.0 kg against 6.3 kg lost; the difference was not significant
2014, 4 weeks	20 young women	Cardio before breakfast against cardio after it, on the same diet	No difference in body fat change
2025 review	99 trials, 6,582 adults	Intermittent fasting against continuous calorie cutting	Similar results overall

Together these give moderate evidence that intermittent fasting helps women lose weight about as well as daily calorie cutting, and no better. The fasted-cardio trial was small and short, so that evidence is early. In the 2025 review, alternate-day fasting lost slightly more (about 1.3 kg), mainly in trials shorter than 24 weeks.

So does intermittent fasting work for women? It does when the fasting hours help you eat less overall. They don’t add extra fat loss on top of that.

Does intermittent fasting affect your period and hormones?

Fasting can affect your period through how much you eat. A change in your periods is the clearest sign that eating less is affecting your hormones. Sudden weight loss and too much exercise are both known causes of stopped periods. If 3 periods in a row don’t come, see a doctor.

The wider problem is called low energy availability, which means eating too little for the energy you use. It harms the health of both women and men who train. Absent periods for more than 6 months caused by over-exercising are also a risk factor for weak bones (osteoporosis).

Some women notice more hunger in the days before their period. If your fasting window feels much harder that week, shortening it is a reasonable response.

Fitting fasting around your cycle

Our women’s fasting planner asks where you are: having periods, on hormonal contraception, perimenopausal, after menopause, or trying to conceive. If you have periods, you enter your cycle length and today’s cycle day. It then shows your likely phase, a suggested window, tips and the signs to stop.

Phase (28-day cycle example)	Window the planner suggests
Period (days 1 to 5)	12:12 to 14:10
Follicular phase, after your period	16:8
Around ovulation	14:10 to 16:8
Luteal phase, after ovulation	14:10
Last days before your period	12:12 to 13:11

These windows are our own suggested framework. No official body gives fasting advice by cycle phase, and there is little research on it. The planner also assumes the textbook 14-day luteal phase. Real cycles vary, mostly in the first half, so treat the phase dates as estimates and go by how you feel.

The best intermittent fasting schedule for women

No trial shows that one intermittent fasting schedule is best for women. Start with a gentle daily schedule such as 12:12 or 14:10, and move up an hour or two at a time if it suits you. Our beginner’s step-by-step plan goes through it week by week.

The two-low-days-a-week pattern from the 2011 trial is an option if daily windows don’t fit your life. Our 5:2 and alternate-day fasting guide explains how fast days work.

Whatever schedule you pick, eat enough in your window. For adult women the protein floor is 0.8 g per kilogram of body weight daily. With regular exercise, the range is about 1.4 to 2.0 g per kg. In a 2013 US obesity guideline, the usual calorie targets for women losing weight start at 1,200 a day. Don’t plan below that without medical help. Our sample week of 16:8 meals builds each day around protein.

Intermittent fasting for women over 40, 50 and 60

Age changes the priorities more than the schedule. After menopause, oestrogen falls, and that can lead to a rapid loss of bone density. Eating enough protein matters more than a longer fast at this stage.

Protein needs rise too. From 65, aim for at least 1.0 to 1.2 g per kg each day. If you are active, aim for 1.2 g or more. A woman of 70 kg would need at least 70 to 84 g a day. One large meal makes those amounts harder to reach. A 14:10 or 16:8 window with two meals may suit you better than one meal a day.

Hashimoto’s disease, the commonest cause of an underactive thyroid, is most common in women and usually starts between 30 and 50. If you take levothyroxine, keep taking it on an empty stomach 30 to 60 minutes before breakfast and before any tea or coffee. Fasting doesn’t change that timing.

Menopause and perimenopause get a guide of their own soon.

When women should not fast

Fasting isn’t advised without medical advice in these situations:

Pregnancy. Trying to lose weight while pregnant is advised against, because it could harm the baby.
Breastfeeding. Speak to your midwife or doctor first. If you drink coffee, keep caffeine to 200 mg a day or less while pregnant or breastfeeding.
Trying to conceive. The planner suggests 12:12 or no fasting, and a conversation with your doctor.
Under 18.
A current or past eating disorder, or being underweight. We advise against fasting here; a doctor can help with the next step.
Diabetes treated with insulin or a sulfonylurea, which can cause low blood sugar.
Polycystic ovary syndrome (PCOS). The 2023 international guideline found no evidence that any one diet beats another. Choose a healthy pattern you can keep up, and ask your doctor before fasting.

Every group is listed on our medical disclaimer page.

Signs to stop and get help

Ease off or stop, and speak to a doctor, if any of these happen:

Your periods become irregular or stop.
Your hair starts shedding a few months after a large weight loss. Losing 9 kg (20 lb) or more can trigger it, and fullness usually returns within 6 to 9 months.
Thoughts about food take over, or a fast often ends in a binge.

For milder problems such as headaches and hunger, see what to do about common side effects.

If you are struggling with food or eating, talk to a doctor. In an emergency, ring your local emergency number. That is 999 in the UK, 112 across the EU, and 911 in the US and Canada. Free helplines for your country are listed at findahelpline.com.

Plan your window for this week

Open the women’s fasting planner, choose where you are, and enter your cycle day if you have periods. It gives you a window for this week and the signs that mean ease off.