{"url":"https://whatshealthyandwhy.com/intermittent-fasting/fasting-and-women","path":"/intermittent-fasting/fasting-and-women","alternates":{"json":"https://whatshealthyandwhy.com/api/articles/intermittent-fasting/fasting-and-women.json","markdown":"https://whatshealthyandwhy.com/intermittent-fasting/fasting-and-women.md"},"topic":{"slug":"intermittent-fasting","name":"Intermittent Fasting","url":"https://whatshealthyandwhy.com/intermittent-fasting"},"slug":"fasting-and-women","order":5,"title":"Fasting and Women: Hormones, Cycles, and Thyroid","question":"Is intermittent fasting different for women?","answer":"It may be: studies in women with obesity show no harm to sex hormones, but few exist, and eating too little can disrupt periods.","description":"Is intermittent fasting different for women? What trials show on sex hormones, periods, PCOS and thyroid medicine, and when to skip fasting.","confidence":2,"confidenceNote":"Few studies, mostly small and in women with obesity; some evidence comes from Ramadan fasting, which differs from other fasting patterns.","evidenceSummary":{"rctCount":1,"observationalCount":2,"metaAnalysisCount":5,"totalParticipants":"600+","replicated":false,"newestStudyYear":2026},"category":{"categoryTitle":"How to Live","categorySlug":"how-to-live","subcategoryName":"Wellness & Lifestyle","subcategorySlug":"lifestyle","url":"https://whatshealthyandwhy.com/explore/how-to-live/lifestyle"},"actions":["Eat enough: in 29 cycling women, hormone signals were disrupted when energy availability fell below about 30 kcal/kg of lean mass a day, a risk with hard training [4].","Note your cycle for a few months. If periods become irregular or stop, ease off and see a clinician; Ramadan studies report mild, temporary irregularities [7].","If you have PCOS, ask your clinician about early time-restricted eating. Small studies show more regular periods and lower androgens, but it is not a substitute for care [3]."],"cautions":["Pregnant, breastfeeding or trying to conceive: ask your clinician first. Ramadan studies show no change in birth weight, but data on other outcomes are insufficient [8].","Thyroid medicine: if you take levothyroxine, ask your clinician to recheck TSH after you change your eating pattern; TSH rose after Ramadan in several studies [9].","Eating-disorder history, underweight, or diabetes medicine (insulin, sulfonylureas): avoid fasting or get supervision, given links to worse eating-disorder symptoms and to low blood sugar [11][12]."],"simpleText":"Maybe, but the research is thin. In women with obesity, trials find weight loss without harmful changes to estrogen or progesterone [1][2], and small studies in polycystic ovary syndrome (PCOS) show lower androgens and more regular periods [3]. But eating too little can disrupt the menstrual cycle [4], and pregnancy, breastfeeding, thyroid medicine and any history of an eating disorder are reasons to ask a clinician first.","mediumText":"How it works\n\nWhat trials in women show. A review of human trials found intermittent fasting lowered androgens (testosterone and the free androgen index) and raised sex hormone-binding globulin in premenopausal women with obesity, especially when eating ended before 4 p.m. Estrogen, gonadotropins and prolactin did not change [1]. A 2026 review of six time-restricted eating (TRE) studies found randomized trials in women with obesity saw no significant change in testosterone, estrogen, progesterone, luteinizing hormone, cortisol or DHEA [2]. In PCOS, three small TRE studies reported more regular cycles in 33% to 40% of women and lower testosterone [3]. A meta-analysis of 13 randomized trials in 612 women with overweight or obesity found TRE lowered weight and fasting insulin without lean mass loss, but did no better than ordinary calorie restriction [5].\n\nWhen fasting becomes too little. The brain's control of the menstrual cycle reacts to energy availability, meaning calories eaten minus calories burned in exercise. In 29 regularly cycling women, hormone pulses stayed normal at 30 kcal per kg of lean mass per day but were disrupted below that [4]. Pairing long fasts with hard training and low intake is where trouble starts.\n\nBlood sugar. In a three-week study of alternate-day fasting in 8 men and 8 women, women's glucose response to a meal was slightly worse afterward, while men's insulin response improved [6]. It is one small study, but it is a reason for women to watch how they respond.\n\nCycles, pregnancy and breastfeeding. Ramadan fasting (daytime only) appears to cause mild, temporary menstrual irregularities without major hormone changes, and pregnant and breastfeeding women are advised to consult a physician because the evidence on safety is inconclusive [7]. Birth weight was unaffected across 22 Ramadan studies, but data on other outcomes were insufficient [8].\n\nThyroid. In healthy adults, Ramadan fasting keeps thyroid function in the normal range. In people on levothyroxine, TSH rose afterward in several studies, though it is unclear whether fasting, medication timing or sleep explains it [9]. See Thyroid health: the master gland.\n\nCycle syncing. We found no randomized trial of fasting schedules matched to menstrual-cycle phases. Even for exercise, a meta-analysis found only trivial, low-quality differences between phases and concluded that general phase-based guidelines cannot be formed [10].\n\nRelated reading: Who should avoid intermittent fasting, PCOS: natural management, and, for the large trials of daily eating windows (TREAT, the NEJM trial) and the CALERIE calorie-restriction trial, Does limiting your eating window help?.","deepText":"The evidence in detail\n\nReviews of hormones. The review of human trials concluded that intermittent fasting reduced androgen markers and raised sex hormone-binding globulin in premenopausal women with obesity, more so when eating ended by 4 p.m.; estrogen, gonadotropins and prolactin were unchanged. In lean, active young men, testosterone fell without loss of muscle mass or strength. The authors stress that very few studies exist [1]. The 2026 systematic review of TRE and female hormones found six studies. Randomized trials in women with a body mass index above 30 consistently showed no significant changes in testosterone, estrogen, progesterone, luteinizing hormone, cortisol, DHEA or sex hormone-binding globulin. Non-randomized PCOS studies reported lower testosterone and luteinizing hormone, possibly confounded by weight loss. The reviewers called TRE hormonally safe in women with general obesity but the evidence inconclusive overall [2]. The PCOS review of three studies reported menstrual regularity in 33% to 40% of women, a 9% fall in testosterone and a 26% fall in the free androgen index, and called for larger trials [3].\n\nWeight and body composition in women. Thirteen randomized trials (612 participants, at least 85% women) found TRE reduced body weight by 1.93 kg (95% CI 0.17 to 3.69) and fasting insulin by 2.12 μU/mL (95% CI 0.07 to 4.17), with no significant effect on BMI, fat mass, fat-free mass, lipids, glucose or blood pressure. Against calorie restriction alone there was no extra weight loss (P = 0.295). Four studies reported minor, self-resolving side effects such as hunger and headache [5].\n\nEnergy availability. In a randomized trial of 29 regularly menstruating, sedentary young women, energy availability was set for 5 days at 10, 20 or 30 kcal per kg of lean body mass per day (with 15 kcal per kg of exercise), against a 45 control. Luteinizing hormone pulse frequency fell, and amplitude rose, below the 30 threshold, and the disruption was greater in women with short luteal phases [4]. This tested energy deficit plus exercise rather than fasting windows, but it shows where the cycle starts to react.\n\nGlucose tolerance. In eight non-obese men and eight non-obese women, 22 days of alternate-day fasting slightly impaired the glucose response to a meal in women (P < 0.01) with unchanged insulin response, while men had no change in glucose response and a lower insulin response (P < 0.03) [6].\n\nPregnancy, breastfeeding and cycles. In 22 studies covering 31,374 pregnancies (18,920 exposed to Ramadan fasting), birth weight was not affected (standardized difference 0.03, 95% CI 0.00 to 0.05) and preterm delivery was not changed (odds ratio 0.99, 95% CI 0.72 to 1.37, from 5,600 pregnancies), but placental weight was lower in fasting mothers and no data existed on perinatal mortality [8]. A 2026 narrative review found Ramadan fasting caused mild, temporary menstrual irregularities with stable fertility hormones, inconclusive and contradictory safety evidence in pregnancy, and some small long-term associations after first-trimester fasting [7].\n\nThyroid. Pooled evidence shows Ramadan fasting preserves hypothalamic-pituitary-thyroid function in healthy adults. In hypothyroid patients on levothyroxine, post-Ramadan TSH rose in several studies while free T4 stayed stable, and no single dosing schedule consistently performed best. Evidence in hyperthyroidism is limited and expert-opinion based [9].\n\nEating-disorder and metabolic cautions. In 491 Chinese adults followed for 8 months, current or past intermittent fasting was associated with higher eating-disorder psychopathology and eating-related impairment at follow-up [11]. In type 2 diabetes treated with insulin or sulfonylureas, intermittent fasting carries an increased hypoglycemia risk [12].\n\nConflicts and gaps. Most trials are short and in women with obesity; we found little in lean, older or postmenopausal women and none testing cycle-phase-timed fasting. Ramadan data (daytime fasting, no fluids) differ from other patterns. Observational links to eating-disorder symptoms cannot show cause.\n\nBottom line (confidence 2 of 5). In women with obesity, intermittent fasting seems hormonally neutral to mildly favorable, and early eating windows may modestly lower androgens. For lean women, athletes, people planning pregnancy, and anyone with a thyroid, diabetes or eating-disorder history, the data are too thin to be casual; use medical guidance and stop if your cycle changes.","deepTruncated":false,"references":[{"id":"1","title":"Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials","authors":"Cienfuegos S, Corapi S, Gabel K, et al.","year":2022,"journal":"Nutrients","pmid":"35684143","url":"https://pubmed.ncbi.nlm.nih.gov/35684143/"},{"id":"2","title":"Impact of time-restricted eating on reproductive hormones and androgen markers in adult females: A systematic review","authors":"Jirapak A, Adams E, Black GM, et al.","year":2026,"journal":"Nutr Health","pmid":"42429418","url":"https://pubmed.ncbi.nlm.nih.gov/42429418/"},{"id":"3","title":"The impact of intermittent fasting on fertility: A focus on polycystic ovary syndrome and reproductive outcomes in Women-A systematic review","authors":"Velissariou M, Athanasiadou CR, Diamanti A, et al.","year":2025,"journal":"Metabol Open","pmid":"39876903","url":"https://pubmed.ncbi.nlm.nih.gov/39876903/"},{"id":"4","title":"Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women","authors":"Loucks AB, Thuma JR","year":2003,"journal":"J Clin Endocrinol Metab","pmid":"12519869","url":"https://pubmed.ncbi.nlm.nih.gov/12519869/"},{"id":"5","title":"Effects of time-restricted eating on body composition and metabolic parameters in overweight and obese women: a systematic review and meta-analysis","authors":"Chen S, Zhang X, Kortas J, et al.","year":2025,"journal":"Front Nutr","pmid":"41036194","url":"https://pubmed.ncbi.nlm.nih.gov/41036194/"},{"id":"6","title":"Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting","authors":"Heilbronn LK, Civitarese AE, Bogacka I, et al.","year":2005,"journal":"Obes Res","pmid":"15833943","url":"https://pubmed.ncbi.nlm.nih.gov/15833943/"},{"id":"7","title":"Exploring the impact of Ramadan fasting on women's reproductive health: A narrative review","authors":"Hussain S, Ahsan S, Ali A, et al.","year":2026,"journal":"Womens Health (Lond)","pmid":"41925301","url":"https://pubmed.ncbi.nlm.nih.gov/41925301/"},{"id":"8","title":"The effect of Ramadan fasting during pregnancy on perinatal outcomes: a systematic review and meta-analysis","authors":"Glazier JD, Hayes DJL, Hussain S, et al.","year":2018,"journal":"BMC Pregnancy Childbirth","pmid":"30359228","url":"https://pubmed.ncbi.nlm.nih.gov/30359228/"},{"id":"9","title":"Ramadan fasting and thyroid function: a narrative review of physiological adaptation and clinical management","authors":"Mohseni S, Mohajeri-Tehrani M, Larijani B, et al.","year":2026,"journal":"J Diabetes Metab Disord","pmid":"42801042","url":"https://pubmed.ncbi.nlm.nih.gov/42801042/"},{"id":"10","title":"The Effects of Menstrual Cycle Phase on Exercise Performance in Eumenorrheic Women: A Systematic Review and Meta-Analysis","authors":"McNulty KL, Elliott-Sale KJ, Dolan E, et al.","year":2020,"journal":"Sports Med","pmid":"32661839","url":"https://pubmed.ncbi.nlm.nih.gov/32661839/"},{"id":"11","title":"Engagement in Intermittent Fasting is Prospectively Associated With Higher Body Mass Index, Higher Eating Disorder Psychopathology, and Lower Intuitive Eating in Chinese Adults","authors":"He J, Chen X, Cui T, et al.","year":2025,"journal":"Int J Eat Disord","pmid":"39530408","url":"https://pubmed.ncbi.nlm.nih.gov/39530408/"},{"id":"12","title":"Intermittent fasting and 'metabolic switch': Effects on metabolic syndrome, prediabetes and type 2 diabetes","authors":"Rajpal A, Ismail-Beigi F","year":2020,"journal":"Diabetes Obes Metab","pmid":"32372521","url":"https://pubmed.ncbi.nlm.nih.gov/32372521/"}],"wordCount":1148,"source":{"path":"src/content/topics/intermittent-fasting/fasting-and-women.md"},"citeAs":"“Is intermittent fasting different for women?.” What's Healthy and Why. https://whatshealthyandwhy.com/intermittent-fasting/fasting-and-women","notice":"General information backed by peer-reviewed research, not medical advice."}