Who This Applies To
Women in their mid-30s to mid-40s who still have regular or near-regular cycles, but whose hormonal landscape is beginning to shift — often with declining anti-Mullerian hormone, potential cycle variability, and increasing metabolic changes.
What Changes
As women move through their late reproductive years, estrogen and progesterone begin a gradual decline. Insulin sensitivity can begin to decrease (meaning you become more insulin resistant), and abdominal fat may begin accumulating even without significant changes in diet or activity. The hormonal flexibility of earlier years starts to narrow.
What the Research Shows
Evidence specifically targeting premenopausal (but not perimenopausal) women is largely drawn from the same time restricted eating (TRE) studies used for reproductive-age women. A 2021 in Experimental Gerontology compared body weight and metabolic risk changes during TRE in premenopausal versus postmenopausal women, providing important baseline data on how the two groups differ.
The 2022 UIC Warrior Diet study followed pre- and post-menopausal obese women for eight weeks on a 4-hour eating window (one of the most aggressive TRE protocols) and notably found no significant change in reproductive hormone levels — including testosterone, androstenedione, estradiol, estrone, and progesterone. However, researchers cautioned that this study focused on women with obesity, limiting generalizability to lean or average-weight premenopausal women.
A 2023 PubMed study found that eight weeks of TRE in women with overweight or obesity led to weight loss without negatively influencing behavioral health parameters, suggesting this population can tolerate structured eating windows well.
Conclusion for Fasting in Premenopausal Women (ages 35-45)
Best-Supported Protocol
The best supported protocol is time restricted eating, daily 14:10 with attention to cycle phase (similar to reproductive women). Earlier eating windows (ending eating by 6–7 PM) are preferred. Premenopausal women may have more flexibility than perimenopausal women, but cycle-syncing fasting remains advisable.
