Real reason intermittent fasting doesn’t work for so many women

Real reason intermittent fasting doesn’t work for so many women,

It has, arguably, been one of the biggest revolutions in weight loss of the past few decades.

At its simplest, intermittent fasting promises something that sounds almost too good to be true: not a punishing list of banned foods, nor a lifetime of calorie-counting, but a simple time limit.

For some, that meant eating only within an eight-hour window each day, skipping breakfast, taking lunch late and finishing dinner by early evening.

For others, it meant the famous 5:2 plan: eating normally for five days a week, then cutting back to around 500 or 600 calories on two fasting days.

And unlike many dieting crazes, intermittent fasting does have genuine scientific backing.

Studies suggest those who stick to such plans typically lose meaningful amounts of weight – often around 7lb to 11lb over ten weeks, while some alternate-day fasting trials have reported losses of up to about 13 percent of body weight.

But it seems not everyone benefits equally.

Some people find the pounds fall away surprisingly quickly. Others are left hungry, irritable and barely any lighter. Now scientists believe they may finally understand one reason why: intermittent fasting appears to affect men and women differently.

Scientists believe they may finally understand why some women can’t lose weight with intermittent fasting: the diet appears to affect men and women differently

Why women don’t lose weight with intermittent fasting

Women do not respond to intermittent fasting in the same way as men – or even in the same way throughout the month.

That is because female hormones are constantly shifting across the menstrual cycle, affecting everything from appetite and energy levels to blood sugar control and how easily the body burns fat.

Experts say two female hormones appear to play the biggest role: estrogen and progesterone.

In the first half of the cycle – after a woman’s period and leading up to ovulation – estrogen gradually rises. 

During this phase, many women find fasting easier, with fewer cravings and steadier energy levels. Researchers believe rising estrogen helps the body regulate blood sugar more effectively and become more efficient at using stored fat for fuel.

But after ovulation, things change.

Levels of progesterone rise in the second half of the cycle – known as the luteal phase, which is the week or two before a period arrives. 

Experts say this happens because rising progesterone slightly increases the body’s energy demands while also making blood sugar less stable. As a result, many women feel hungrier, crave more carbohydrates and cope less well with long fasting periods.

This may help explain why some women report feeling shaky, exhausted, irritable or intensely hungry if they attempt long fasts just before their period.

Clinical studies have also linked fasting during this phase to poorer sleep, blood sugar crashes and worsening PMS symptoms in some women.

‘Women’s bodies are hormonally dynamic, with estrogen and progesterone shifting throughout the month,’ said Dr Kellyann Petrucci, a board-certified naturopathic physician.

‘Fasting can act as a form of stress for some, and when that stress overlaps with natural hormonal fluctuations, it may impact blood sugar balance, metabolism and reproductive signals.

‘That’s why overly rigid fasting schedules don’t always work well for women.’

Actress Jennifer Aniston, 57, has admitted to fasting for 16 hours daily. Research shows women respond better to this diet plan when they reach perimenopause and menopause

Experts say the picture changes again during perimenopause and menopause.

As estrogen levels decline and periods become irregular or stop altogether, some women find they can tolerate longer fasting windows more easily because the monthly hormonal swings become less dramatic.

‘Hormones, along with things like blood sugar, appetite, sleep and stress response, all shift across the month, so a fasting window that feels great one week can feel draining the next,’ said Elle Serafina, a California-based nutrition health coach.

Below, the Daily Mail explains what happens in each phase of the menstrual cycle – and how some experts believe women can adapt intermittent fasting plans to work with their hormones rather than against them.

Days 1 to 5: Menstruation

The first phase of the menstrual cycle is menstruation – when a woman has her period.

At this point, levels of both estrogen and progesterone have dropped sharply after the body realizes pregnancy has not occurred – triggering the womb lining to shed as a period begins.

Experts say this can leave many women feeling more tired, hungrier and less able to tolerate aggressive fasting routines.

The body is also losing blood, iron and other nutrients, meaning energy levels are often naturally lower.

For this reason, some experts advise against long fasting windows or punishing exercise during this phase.

Instead, they recommend gentler fasting schedules – typically around 12 to 14 hours overnight.

Liza Baker, a health coach specializing in midlife women, said: ‘I personally have found that 12 to 14 hours is a great, sustainable fasting window for myself and most of my clients.

‘Think about it: if you don’t eat for three hours before bed and you sleep for eight hours, you’ve already gone 11 hours fasting. If you have a morning routine before you sit down to eat, there’s your extra one to three hours.’

Elle Serafina, a California-based nutrition health coach, said women may also benefit from focusing on comforting, nutrient-rich foods during this stage of the cycle rather than pushing through strict fasting plans.

‘During menstruation, warm, easily digestible mineral-rich meals are often better than strict fasting; slow-cooked soups, stews, broths, lentil soups and other warming meals,’ she said.

Broadcaster Meghan McCain attacked the intermittent fasting trend for promoting ‘disordered eating’, specifically criticizing celebrities who promote extreme versions of it

Days 6–12: The follicular phase

After a period ends, estrogen levels begin to rise again as the body prepares to release an egg during ovulation.

Experts say this appears to be the point in the cycle when many women tolerate fasting best.

Research suggests rising estrogen may help the body become more metabolically flexible – meaning it can switch more easily between burning carbohydrates and stored fat for energy. Blood sugar also tends to be more stable during this phase, which may help reduce hunger and energy crashes.

Dr Robert Boyd, a naturopathic doctor based in Virginia, told the Daily Mail: ‘The follicular phase is usually more forgiving.

‘After menstruation through ovulation, energy tends to be more stable, blood sugar regulation is smoother, and many women tolerate a longer fasting window without issue.

‘That’s often when fasting feels easiest.’

Because of this, some experts believe this is the best time in the month for women who want to try slightly longer fasting windows, such as 16 to 18 hours.

Some experienced fasters may also tolerate occasional longer fasts during this phase more comfortably than at other points in the cycle.

Experts say many women report steadier energy, fewer cravings and faster weight-loss progress during this stage.

Days 13–15: Ovulation 

Around ovulation – when the ovary releases an egg – estrogen rises sharply to help trigger the release of the egg before dropping again soon afterwards.

Experts say this rapid hormonal shift can make fasting feel less predictable for some women.

While some continue to feel energetic, others may notice headaches, irritability, disrupted sleep or sudden hunger swings around this point in the cycle.

Researchers believe this happens because rapidly changing hormone levels can temporarily affect blood sugar regulation, appetite and the body’s stress response.

Registered dietitian Lisa Moscovitz told the Daily Mail: ‘Because intermittent fasting can cause disruptions to ovulation and hormone balance, women may notice worsening PMS symptoms like acne, bloating and irritability.’

Experts say these symptoms may be a sign the body is under too much stress.

Rather than pushing through aggressive fasting schedules, some recommend switching to gentler forms of time-restricted eating during this phase – such as a 12- to 14-hour overnight fast.

That could mean finishing dinner at 6pm and eating breakfast at 8am the following morning.

Actress Mindy Kaling dismissed the 16:8 fasting method – fasting for 16 hours and eating within an eight hour window – in a tweet, writing: ’16:8 more like 16 hate’

Days 16–28: The luteal phase

The second half of the menstrual cycle – known as the luteal phase – is often considered the most difficult time for women to fast.

After ovulation, progesterone becomes the dominant hormone as the body prepares for a possible pregnancy.

Experts say this appears to slightly increase the body’s energy demands while also making blood sugar less stable. As a result, many women feel hungrier, crave more carbohydrates and cope less well with long fasting periods.

Stress hormones such as cortisol may also rise more easily during this phase, potentially leaving women feeling more anxious, irritable or exhausted if they combine strict fasting with an already hormonally demanding stage of the cycle.

‘The phase that gives women the most trouble is the luteal phase,’ Dr Robert Boyd said.

‘Progesterone is elevated, insulin sensitivity tends to dip, appetite and cravings go up, and the nervous system is generally more reactive.

‘Stacking a strict fasting window on top of all that often makes things worse, not better.’

Experts say aggressive fasting during this phase may also worsen PMS symptoms, contribute to blood sugar crashes and disrupt sleep.

For this reason, some recommend stepping back from longer fasting windows entirely in the days before a period.

Instead, women may benefit more from regular, protein-rich meals that help keep blood sugar stable and reduce cravings.

For those who still wish to fast during this stage, experts generally advise keeping fasting windows shorter and more flexible – such as a gentle 14-hour fast which could be done overnight, rather than rigid 16-hour restrictions. 

Perimenopause and menopause: Why fasting may feel easier again

Once women enter perimenopause – the years leading up to menopause – hormone patterns begin to change dramatically.

Periods become irregular, estrogen levels fluctuate unpredictably and progesterone often falls first.

Experts say this can make some women more sensitive to aggressive fasting routines, particularly if they are already dealing with symptoms such as fatigue, poor sleep, anxiety or blood sugar swings.

‘Women with conditions like PCOS, perimenopause symptoms, or hypothalamic amenorrhea may be more sensitive,’ Dr Kellyann Petrucci, a naturopathic doctor and nutritionist, told the Daily Mail.

‘A gentler approach – focused on balanced blood sugar, deeply nourishing foods and consistency – tends to be more supportive.’

However, after menopause itself – when periods stop completely – many women report fasting becomes easier again.

Researchers believe this may be because the dramatic monthly hormonal fluctuations linked to the menstrual cycle disappear, particularly the progesterone-driven changes in appetite and carbohydrate needs seen before periods.

Even so, experts warn that postmenopausal women may still be sensitive to stress hormones such as cortisol, meaning extreme fasting plans can still backfire.

For this reason, many recommend starting cautiously with moderate fasting windows – such as 12 to 14 hours overnight several times a week – rather than jumping straight into prolonged fasts.

Dr Robert Boyd, a naturopathic doctor based in Virginia

Warning signs fasting may be doing more harm than good

Experts stress that intermittent fasting is not inherently harmful for women – but they say rigid, one-size-fits-all approaches may ignore how dramatically female biology changes across the month.

Instead, many now believe fasting plans work best when adapted to hormonal shifts, energy levels and stress tolerance.

Dr Robert Boyd said: ‘The bigger red flags I watch for are worsening PMS, hair shedding, dizziness, irregular cycles, or that “wired but tired” feeling that doesn’t resolve with rest.

‘Any of those usually tells me the fasting window is too long, overall calories are too low, or there’s too much other stress in the picture.

‘Fasting plus intense training plus a calorie deficit is a combination I see backfire a lot.’

Experts also warn that intermittent fasting may not be appropriate for everyone.

‘You should avoid intermittent fasting or speak with a doctor first if you are pregnant, breastfeeding, or trying to conceive,’ Dr Jeffrey Kraft, a bariatric surgeon at Hackensack Meridian Palisades Medical Center, said.

‘Your body needs consistent nutrients to support you and your baby.’