Every claim, every source.

This 2025 systematic review specifically addresses how intermittent fasting affects fertility and reproductive hormones in women with polycystic ovary syndrome (PCOS) — the most common endocrine disorder of reproductive-aged women, characterized by hyperandrogenism, insulin resistance, and menstrual irregularity. The authors synthesized three included studies of time-restricted feeding (TRF) and related IF protocols in PCOS patients. The findings were notably favorable. Menstrual regularity improved in 33–40 percent of participants — meaning a third or more of women with previously irregular cycles reported normalized cycling after TRF intervention. Hormonal changes pointed in the right direction for the PCOS phenotype: total testosterone fell about 9 percent, free androgen index dropped 26 percent, sex hormone-binding globulin rose, and anti-Müllerian hormone and luteinizing hormone both decreased. The review concludes that intermittent fasting, particularly time-restricted feeding, shows potential as a non-pharmacological adjunct intervention for improving reproductive health and fertility in women with PCOS by addressing the core pathophysiological mechanisms (insulin resistance, hyperandrogenism) that drive the syndrome.

This Nutrients review is the first to synthesize specifically what human trials of intermittent fasting (not animal work, not religious fasting) show about sex-hormone shifts in women and men. The authors identified seven human trials total: five testing time-restricted eating, one testing a 5:2 protocol, and one studying meal timing. Their headline findings for premenopausal women with obesity: intermittent fasting reduces testosterone and the free androgen index, and increases sex hormone-binding globulin — particularly when the eating window is restricted to earlier in the day. Estrogen, luteinizing hormone, and follicle-stimulating hormone showed no statistically meaningful change in the trials reviewed. In men, intermittent fasting reduced total and free testosterone in some studies, with implications for libido and lean-mass maintenance that the authors flag as concerning at longer protocol durations. The honest summary: female reproductive hormone effects are real but modest, mostly favorable for PCOS-spectrum profiles, and depend heavily on eating-window timing.

This study used data from the Canadian Study of Adolescent Health Behaviors — a national survey of 2,762 adolescents and young adults — to ask how common intermittent fasting is and whether it correlates with eating-disorder behaviors. The engagement numbers were striking: roughly 48 percent of women, 38 percent of men, and 52 percent of transgender or gender-non-conforming respondents reported practicing some form of intermittent fasting in the past 12 months. The researchers used the Eating Disorder Examination Questionnaire alongside modified Poisson regression to measure associations. Across all three gender groups, intermittent fasting in the past 12 months and the past 30 days was significantly associated with elevated eating-disorder psychopathology — disordered cognitions, restrictive behaviors, and binge-purge cycles. The pattern was strongest and most consistent in women. The authors do not claim fasting causes eating disorders; the data are cross-sectional and cannot prove direction. They argue clinicians screening young patients should treat self-reported intermittent fasting as a meaningful flag.

This EFSA Scientific Committee statement weighs the cardiovascular and neurodevelopmental benefits of fish consumption against the risks of methylmercury exposure across the European population. It builds on EFSA's 2012 opinion which set the tolerable weekly intake (TWI) for methylmercury at 1.3 µg/kg body weight — meaning a 70 kg adult can safely consume about 91 µg/week. The 2015 statement identifies the dominant European mercury sources by species: tuna (the largest single contributor in adult diets), swordfish, cod, whiting, and pike. Notably, sardines are not on this high-mercury list. The statement acknowledges new epidemiological data (Seychelles cohort) showing that the long-chain omega-3s from fish may counteract some methylmercury toxicity — a benefit-risk tradeoff that favors lower-mercury species like sardines. EFSA's conclusion is risk-tiered: vulnerable groups (pregnant women, children, high-fish consumers up to 6× TWI) should choose lower-mercury species; the general adult population can consume fish at moderate intake without exceeding the TWI.

This JAMA evidence synthesis remains the most-cited single statement on whether fish consumption is, on balance, beneficial or harmful given the dual presence of cardioprotective omega-3 fatty acids and contaminants like methylmercury and PCBs. Mozaffarian and Rimm reviewed the strength of evidence on both sides for adults and for vulnerable groups (children, women of childbearing age) and reached an unambiguous conclusion: the benefits dominate the risks for adult populations. Their pooled estimate found that modest fish consumption — 1–2 servings per week, particularly fatty species rich in EPA and DHA — reduces coronary death risk by 36 percent and total mortality by 17 percent. They identified an EPA+DHA intake of about 250 mg/day as sufficient for primary cardiovascular prevention. For pregnant women and young children, they recommended species selection to minimize methylmercury exposure (avoiding swordfish, king mackerel, tilefish, shark) while still consuming two servings of lower-mercury fish per week. The paper's framing — benefits substantially outweigh risks — has anchored most subsequent dietary fish guidance.

This is one of the foundational human alternate-day fasting trials, and — importantly — the actual source of the famous "57 percent insulin drop" claim that circulates widely in popular fasting content. Sixteen nonobese adults (8 men, 8 women) fasted every other day for 22 days. The protocol alternated full fasting days with normal eating days. Body weight dropped 2.5 percent and fat mass dropped 4 percent over the three weeks. Resting metabolic rate did not change significantly through day 21, but respiratory quotient fell on day 22 — indicating a clear shift toward fat oxidation, with daily fat oxidation rising by 15 grams or more. Glucose and ghrelin remained essentially stable, but fasting insulin dropped 57±4 percent. Hunger on fasting days remained elevated throughout the protocol, suggesting that adaptation to alternate-day hunger patterns does not happen quickly. The paper concluded that alternate-day fasting is feasible in nonobese adults and produces substantial fat-oxidation and insulin-sensitivity shifts, but adherence is challenging.

Anne Loucks's 2003 review consolidates a foundational principle for women's exercise and nutrition science: it is energy availability — calories left over after subtracting exercise expenditure from intake — that regulates reproductive function, not body fatness. Through a series of careful in-laboratory studies measuring LH (luteinizing hormone) pulsatility as a surrogate for menstrual cycle integrity, Loucks and colleagues found that reproductive disruption begins when energy availability falls below a threshold between 20 and 30 kcal per kilogram of lean body mass per day. Above the threshold, women maintain normal reproductive endocrine function; below it, even with adequate body fat, LH pulsatility breaks down and menstrual disruption follows. The implication is that "thinness" itself does not cause amenorrhea; sustained energy deficit does. The framework gave rise to the modern Female Athlete Triad and RED-S (Relative Energy Deficiency in Sport) clinical concepts, which are now standard in sports medicine. The 30 kcal/kg LBM/day threshold remains the most-cited clinical cutoff for evaluating energy-availability risk in active women.