Fasting for women

Search online and you'll find strong claims that fasting "wrecks" women's hormones, or that it works completely differently for women. The real picture is calmer. Most fasting trials include women, and moderate daily fasting appears safe and effective for most. But female hormones do respond to a lack of energy, and some situations, such as pregnancy, call for a different approach.

What happens to your hormones

Researchers at the University of Illinois reviewed every human trial they could find on fasting and reproductive hormones. In premenopausal women with obesity, fasting tended to lower androgens, the group of hormones that includes testosterone, and to raise SHBG, a protein that keeps them in check. It had no effect on estrogen, on the brain hormones that control ovulation, or on prolactin ¹.

Energy, not timing, is what your cycle notices

Your menstrual cycle depends on regular pulses of a hormone called LH, released by the brain. When the body doesn't get enough energy, those pulses can falter. In a careful study, young women exercised daily while researchers controlled exactly how much energy they had left over after exercise. LH pulses stayed normal at moderate levels, and were disrupted only when energy fell well below what the body needed ⁴.

PCOS

Polycystic ovary syndrome is one of the most common hormonal conditions in women, and it often involves high androgens and insulin resistance. Since fasting tends to lower both, researchers have started testing it.

Menopause

Many women find it harder to manage their weight around menopause, and some wonder whether fasting still works. A pooled analysis of three 12-week trials of alternate-day fasting found that it did. Premenopausal women, postmenopausal women and men all lost a similar share of their weight, along with similar drops in fat, insulin and blood pressure ³.

When not to fast

Eating disorders are another reason for caution. In adults with obesity, alternate-day fasting didn't increase disordered eating, and binge eating actually decreased ⁵. But those studies didn't include people with a history of eating disorders. If that's you, structured fasting isn't recommended without support from a professional.

Sources

1. Cienfuegos S, Corapi S, Gabel K, et al. Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. Nutrients. 2022;14(11):2343. doi.org/10.3390/nu14112343
2. Li C, Xing C, Zhang J, et al. Eight-hour time-restricted feeding improves endocrine and metabolic profiles in women with anovulatory polycystic ovary syndrome. J Transl Med. 2021;19(1):148. doi.org/10.1186/s12967-021-02817-2
3. Lin S, Lima Oliveira M, Gabel K, et al. Does the weight loss efficacy of alternate day fasting differ according to sex and menopausal status? Nutr Metab Cardiovasc Dis. 2021;31(2):641-649. doi.org/10.1016/j.numecd.2020.10.018
4. Loucks AB, Thuma JR. Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women. J Clin Endocrinol Metab. 2003;88(1):297-311. doi.org/10.1210/jc.2002-020369
5. Hoddy KK, Kroeger CM, Trepanowski JF, et al. Safety of alternate day fasting and effect on disordered eating behaviors. Nutr J. 2015;14:44. doi.org/10.1186/s12937-015-0029-9