It has undoubtedly been one of the most significant advancements in weight loss during the previous few decades.
In its most basic form, intermittent fasting offers something that seems almost too wonderful to be true: a straightforward time limit rather than a harsh list of forbidden foods or a lifetime of calorie watching.
For some, this meant foregoing breakfast, eating just within an eight-hour window every day, having a late lunch, and finishing dinner by early evening.
For others, it meant following the well-known 5:2 regimen, which calls for eating a regular diet five days a week and reducing caloric intake to about 500 or 600 on two days of fasting.
Additionally, intermittent fasting has actual scientific support, in contrast to many dietary fads.
According to studies, people who follow these regimens usually lose significant amounts of weight—typically between 7 and 11 pounds over the course of ten weeks—while some alternate-day fasting trials have recorded weight loss of up to 13 percent.
However, it appears that not everyone gains equally.
For some, the weight loss happens remarkably fast. Others are left marginally lighter, hungry, and agitated. Scientists now think they may finally understand why: men and women seem to react differently to intermittent fasting.
Because the diet seems to effect men and women differently, scientists think they may now understand why some women are unable to lose weight with intermittent fasting.
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Why intermittent fasting doesn’t help women lose weight
Women’s reactions to intermittent fasting differ from men’s, and they also change over the course of the month.
This is due to the fact that female hormones are continuously changing throughout the menstrual cycle, impacting everything from blood sugar regulation and the body’s ability to burn fat to hunger and energy levels.
According to experts, progesterone and oestrogen seem to be the two female hormones that are most important.
Oestrogen progressively increases during the first half of the cycle, which follows a woman’s menstrual cycle and before ovulation.
Many women feel that fasting is simpler during this stage, with less cravings and more consistent energy levels. Rising oestrogen, according to researchers, improves blood sugar regulation and the body’s ability to use stored fat as fuel.
However, things change following ovulation.
Progesterone levels increase during the luteal phase, the second half of the cycle that occurs one or two weeks before to the onset of menstruation.
According to experts, this occurs because increased progesterone makes blood sugar less stable and somewhat raises the body’s energy requirements. Because of this, many women experience increased hunger, a greater desire for carbohydrates, and difficulty enduring extended fasts.
This could help explain why some women who try lengthy fasts right before their period report feeling shaky, tired, agitated, or extremely hungry.
Clinical research has also connected fasting at this stage to worsened PMS symptoms in certain women, blood sugar falls, and decreased sleep.
According to board-certified naturopathic physician Dr. Kellyann Petrucci, “women’s bodies are hormonally dynamic, with oestrogen and progesterone shifting throughout the month.”
“Overly strict fasting schedules don’t always work well for women because fasting can act as a form of stress for some people, and when that stress coincides with natural hormonal fluctuations, it may impact blood sugar balance, metabolism, and reproductive signals.”
Jennifer Aniston, a 57-year-old actress, has acknowledged that she fasts for sixteen hours every day. According to research, women who enter perimenopause and menopause respond better to this food plan.
According to experts, the picture shifts once more throughout menopause and perimenopause.
Some women find that the monthly hormonal swings become less dramatic when oestrogen levels drop and periods become irregular or cease entirely, making prolonged fasting windows easier for them to endure.
‘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.
According to experts, this can make many women feel more exhausted, hungry, and less able to handle rigorous fasting schedules.
Additionally, the body is losing iron, blood, and other nutrients, which naturally lowers energy levels.
Because of this, several doctors advise against punishing activity or extended periods of fasting during this phase.
Rather, they suggest more moderate fasting periods, usually lasting 12 to 14 hours at night.
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
The follicular phase, days 6–12
Oestrogen levels start to increase again after a period ends when the body gets ready to release an egg during ovulation.
According to experts, many women seem to be able to handle fasting the best at this stage of the cycle.
According to research, the body may become more metabolically flexible when oestrogen levels rise, making it easier for the body to switch between burning stored fat and carbs for energy. Additionally, blood sugar tends to be more constant throughout this phase, which may lessen energy dumps and appetite.
The Daily Mail was informed by Virginia-based naturopathic physician Dr. Robert Boyd that “the follicular phase is usually more forgiving.”Energy tends to be more consistent after menstruation through ovulation, blood sugar management is more seamless, and many women can easily endure a longer fasting window. “That’s often when fasting feels easiest.”
For women who wish to try somewhat longer fasting windows, like 16 to 18 hours, this is the ideal time of month, according to some specialists.
Additionally, some seasoned fasters might find it easier to endure sporadic longer fasts during this phase than at other stages of the cycle.
Many women experience more consistent energy, less cravings, and quicker weight loss during this phase, according to experts.
Days 13–15: Ovulation
Oestrogen increases dramatically around ovulation, when the ovary releases an egg, to aid in the release of the egg before rapidly declining once more.
According to experts, some women may find fasting less predictable as a result of this quick hormonal change.
Around this time in the cycle, some people may have headaches, irritability, disturbed sleep, or abrupt swings in hunger, while others may still feel energised.
Researchers think this occurs because the body’s stress reaction, appetite, and blood sugar regulation can all be momentarily impacted by quickly fluctuating hormone levels.
“Because intermittent fasting can cause disruptions to ovulation and hormone balance, women may notice worsening PMS symptoms like acne, bloating, and irritability,” Lisa Moscovitz, a registered nutritionist, told the Daily Mail.
According to experts, these symptoms could indicate that the body is experiencing excessive stress.
Some advise moving to more benign kinds of time-restricted eating during this phase, such as a 12- to 14-hour overnight fast, instead of enforcing severe fasting schedules.
This could entail having dinner at 6 p.m. and breakfast at 8 a.m. the next day.
In a tweet, actress Mindy Kaling mocked the 16:8 fasting regimen, which involves fasting for 16 hours and eating inside an eight-hour window, saying, “16:8 more like 16 hate.”
The luteal phase, days 16–28
The luteal phase, which is the second half of the menstrual cycle, is frequently regarded as the most challenging period for women to fast.
Progesterone takes over as the primary hormone following ovulation as the body gets ready for a potential pregnancy.
According to experts, this seems to make blood sugar less stable and somewhat raise the body’s energy requirements. Because of this, many women experience increased hunger, a greater desire for carbohydrates, and difficulty enduring extended fasts.
“The phase that gives women the most trouble is the luteal phase,” Dr. Robert Boyd stated. “Progesterone is elevated, insulin sensitivity tends to dip, appetite and cravings go up, and the nervous system is generally more reactive.” Stress hormones like 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.
“Adding a rigorous fasting window to all of that frequently makes things worse, not better.”
Aggressive fasting during this stage, according to experts, may potentially exacerbate PMS symptoms, cause blood sugar dips, and interfere with sleep.
Because of this, some advise avoiding prolonged fasting windows completely in the days leading up to menstruation.
Rather, frequent, high-protein meals that lower cravings and stabilise blood sugar may be more beneficial to women.
Experts typically recommend keeping fasting windows shorter and more flexible for those who still want to fast during this phase. For example, a mild 14-hour fast that might be completed overnight is preferable to rigorous 16-hour limits.
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Menopause and perimenopause: Why it could be simpler to fast again
Hormone rhythms start to drastically alter once women reach perimenopause, the years preceding menopause.
Progesterone frequently declines first, oestrogen levels fluctuate erratically, and periods become irregular.
“Women with conditions like PCOS, perimenopause symptoms, or hypothalamic amenorrhoea 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.” Experts say this can make some women more sensitive to aggressive fasting routines, especially if they are already dealing with symptoms like fatigue, anxiety, or blood sugar swings.”
However, many women claim that fasting becomes easier again after menopause, when periods end entirely.
Researchers speculate that this could be due to the disappearance of the substantial monthly hormonal oscillations associated with the menstrual cycle, especially the progesterone-driven alterations in hunger and carbohydrate requirements observed prior to periods.
However, experts caution that extreme fasting regimens may still backfire because postmenopausal women may still be sensitive to stress chemicals like cortisol.
Because of this, rather than immediately embarking on extended fasts, many advise beginning slowly with moderate fasting periods, such as 12 to 14 hours overnight multiple times a week.
Virginia-based naturopathic physician Dr. Robert Boyd
Warning indicators that fasting could be more detrimental than beneficial
Although experts emphasise that intermittent fasting is not intrinsically bad for women, they caution that strict, one-size-fits-all methods can overlook how significantly female biology varies during the month.
Rather, many now think that fasting regimens are most effective when they are tailored to hormonal changes, energy levels, and stress tolerance.
“The bigger red flags I watch for are worsening PMS, hair shedding, dizziness, irregular cycles, or that “wired but tired” feeling that doesn’t go away with rest,” stated Dr. Robert Boyd. “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.”
“I frequently see the combination of intense training, fasting, and a calorie deficit backfire.”
Intermittent fasting may not be suitable for everyone, according to experts. “If you are pregnant, nursing, or trying to conceive, you should avoid intermittent fasting or speak with a doctor first,” said Dr. Jeffrey Kraft, a bariatric surgeon at Hackensack Meridian Palisades Medical Center. “Your body needs consistent nutrients to support you and your baby.”
