Time-Restricted Eating Does Not Change Sex Hormones in Women or Men With Obesity: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

One of the most common concerns about intermittent fasting — particularly for women — is whether it disrupts sex hormones. Headlines and social media posts regularly claim that fasting raises or lowers estrogen, testosterone, or progesterone in ways that could harm reproductive health or general wellbeing.

This study from the Varady lab at the University of Illinois at Chicago directly tested that question. The researchers wanted to know: does time-restricted eating change sex hormone levels in men and women with obesity, compared to daily calorie restriction or no dietary change at all? And does it affect premenopausal and postmenopausal women differently?

The study follows a long line of research from the same team, which has previously established that time-restricted eating produces meaningful weight loss without requiring calorie counting — but the hormone question had not been fully answered in a year-long trial.

Who Was Studied

Participant profile: Adults with obesity (BMI qualifying for obesity classification). The female participants were sub-grouped by menopausal status — premenopausal and postmenopausal — to detect any differential hormone effects. Male participants were included to allow sex-based comparisons.

How 8-hour TRE worked in this study: Participants ate all food between 12:00 pm and 8:00 pm, seven days a week. No calorie counting or food restrictions were applied — participants could eat whatever they chose during the eating window. Outside those hours, only water, black coffee, and other non-caloric beverages were permitted.

What the Researchers Found

Body Weight

Both the TRE and calorie restriction groups lost significantly more weight than controls by month 12 (P < 0.01). This was consistent across males, premenopausal females, and postmenopausal females. The degree of weight loss was comparable between TRE and CR — confirming that simply restricting the eating window to eight hours is as effective as a structured 25% calorie reduction for weight management in adults with obesity.

Sex Hormones

• None of the sex hormones measured changed significantly over 12 months in either intervention group, relative to controls
• This was true for males, premenopausal females, and postmenopausal females separately
• TRE did not raise or lower testosterone in any group
• TRE did not raise or lower estrogen markers in postmenopausal women
• DHEA remained stable in all groups throughout the 12-month period

What Did Not Change

• Sex hormone-binding globulin (SHBG)
• Dehydroepiandrosterone (DHEA)
• All estrogen markers in postmenopausal women
• Testosterone in both sexes
• No significant difference in hormone outcomes between TRE and calorie restriction

What the Researchers Concluded

Time-restricted eating produces body weight reduction comparable to daily calorie restriction in adults with obesity, but neither intervention changes circulating sex hormone concentrations over a 12-month period in males, premenopausal females, or postmenopausal females.

What This Means If You Fast

• Fasting is unlikely to disrupt your hormones through its direct effects on sex hormones. Over 12 months of daily 8-hour TRE, testosterone, estrogen, progesterone, DHEA, and SHBG remained stable in both men and women.
• Weight loss from fasting may still affect hormones indirectly. This study controlled for the direct effect of the fasting window — but weight loss itself can influence hormone levels in overweight individuals, typically in a beneficial direction (lower androgen excess in women with PCOS, improved estrogen metabolism in overweight postmenopausal women).
• The fear that "fasting will disrupt my hormones" is not supported by this data. A year of daily time-restricted eating did not measurably alter sex hormone levels in this population.
• Both TRE and calorie restriction produced similar weight loss. If you find calorie counting unsustainable, 16:8 time-restricted eating is a validated alternative that achieves comparable results.
• Menopausal status did not change the outcome. Premenopausal and postmenopausal women showed the same pattern: weight loss without hormonal disruption.
• Context matters. This study was conducted in adults with obesity. Results may differ in lean women, women with hormonal conditions such as PCOS, or women doing more aggressive protocols than 8-hour TRE.

Study Limitations

• Small sample size. 90 participants divided into three groups gives approximately 30 per arm — a relatively modest number for detecting subtle hormonal changes.
• Single sex hormone panel. Hormones were measured at discrete time points, not continuously. Fluctuations within the month or across the menstrual cycle may not have been captured.
• Menstrual cycle phase not controlled. Premenopausal women's hormone levels naturally vary by 30–60% across the cycle. Measurements not timed to cycle phase add variability to results.
• Self-reported food intake. Adherence to the eating window was largely self-reported, which introduces the possibility that some participants did not strictly follow the protocol.
• Obesity population only. Results apply specifically to adults with obesity. The effect of TRE on sex hormones in normal-weight individuals, or in women with hormonal conditions, may differ.
• No tracking of menstrual cycle regularity. The study did not report on whether TRE affected menstrual regularity or ovulation — only on circulating hormone concentrations.
• Funding not disclosed in the available abstract, limiting assessment of potential conflicts of interest.

Source

Lin S, Cienfuegos S, Ezpeleta M, Pavlou V, Runchey MC, Varady KA. (2024). Effect of time restricted eating versus daily calorie restriction on sex hormones in males and females with obesity. European Journal of Clinical Nutrition, 78(9), 814–817. PMID: 38798539

Frequently Asked Questions

Does intermittent fasting lower estrogen in women?

Based on this 12-month randomized trial, 8-hour time-restricted eating did not change estrogen (estradiol or estrone) levels in postmenopausal women with obesity compared to calorie restriction or control. Direct estrogen measurements in premenopausal women were not reported separately in this study.

Will intermittent fasting raise or lower my testosterone?

In this study, total testosterone remained unchanged after 12 months of 8-hour TRE in both males and females with obesity. Neither TRE nor a 25% calorie restriction produced a significant change in testosterone levels in any group.

Can fasting disrupt progesterone?

This study found no change in progesterone levels in postmenopausal women following 12 months of TRE. However, the question of progesterone disruption in premenopausal women who fast aggressively — particularly in the luteal phase — is a separate question that this study was not designed to answer and did not measure directly.

Is time-restricted eating as effective as calorie counting for weight loss?

In this trial, both 8-hour TRE and 25% daily calorie restriction produced comparable weight loss after 12 months in adults with obesity. The TRE group achieved similar results without calorie counting, suggesting it may be a more sustainable approach for those who find calorie tracking difficult to maintain.

Should women with PCOS worry about intermittent fasting affecting their hormones?

This study did not specifically examine women with PCOS. For women with PCOS — where androgen excess and insulin resistance are common features — the hormonal effects of fasting may differ from those in this general obesity population. Consult a healthcare provider before starting any fasting protocol if you have PCOS.

Related Research and Articles

• Intermittent fasting benefits: the complete science-backed guide
• How intermittent fasting affects women's hormones
• Intermittent fasting and PCOS: what the research shows
• What is the 16:8 intermittent fasting protocol?
• Can intermittent fasting improve insulin sensitivity?
• Intermittent fasting and weight loss: what 50 studies show
• Intermittent fasting for women: the complete beginner's guide

Want the complete guide to fasting? Get Intermittent Fasting in Practice on Amazon — and claim 3 months free on our fasting app at fastinginpractice.com/redeem.