Does Skipping Breakfast Impact Menstrual Health? A Review for Dietitians

The relationship between nutrition and reproductive health is well established, but some research suggests that when food is consumed may be just as critical as what is eaten. Meal timing influences hormonal rhythms, ovulation, and menstrual function through pathways tied to the circadian system and energy sensing.

For dietitians supporting clients with cycle irregularities, hypothalamic amenorrhea, or PCOS, understanding these mechanisms is essential for providing nuanced, evidence-informed care.

Meal Timing and Menstrual Cycle Health: What Dietitians Should Know

The reproductive system is governed by a tightly regulated hormonal cascade known as the hypothalamic–pituitary–gonadal (HPG) axis. Central to this axis is gonadotropin-releasing hormone (GnRH), released in a pulsatile manner from the hypothalamus. GnRH stimulates the pituitary to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn regulate ovulation and the production of ovarian hormones.

Two major mechanisms are implicated: circadian rhythm alignment and metabolic signaling through hormones like leptin and cortisol.

Circadian Rhythm: The Body’s Timekeeper

The circadian system orchestrates daily rhythms in hormone secretion, metabolism, and behavior. A central clock located in the suprachiasmatic nucleus (SCN) of the brain synchronizes with peripheral clocks in tissues such as the liver, adipose tissue, ovaries, and uterus. This synchronization is crucial for reproductive health, particularly for the pulsatile release of GnRH [1].

Meal timing serves as a powerful external cue—known as a zeitgeber—that can reset peripheral clocks independently of the central SCN. When food intake occurs early in the day, it reinforces the alignment of internal clocks and supports stable hormonal signaling. Conversely, irregular or delayed meal patterns can desynchronize circadian rhythms, impairing the hormonal cascade that governs ovulation [1][2].

Leptin, Cortisol, and Energy Signalling

Even in the absence of overt caloric restriction, delayed or inconsistent eating patterns can mimic an energy deficit at the hormonal level.

• Leptin, an adipokine secreted in proportion to energy stores, plays a key role in signaling energy sufficiency to the hypothalamus. Low leptin levels, which can result from fasting or meal skipping, have been shown to suppress GnRH secretion, thereby reducing LH and FSH output and disrupting ovulatory function [1].

• Cortisol, another major player, rises in response to fasting or stress and can blunt GnRH pulsatility. This dual impact—low leptin and high cortisol—can create a hormonal environment unfavourable to regular ovulation, even in individuals with a normal BMI or calorie intake.

These mechanisms are central to the understanding of functional hypothalamic amenorrhea (FHA), a condition marked by the absence of menstruation due to stress, energy deficiency, or overexercise. Importantly, individuals with high dietary restraint but without overt undernutrition can still present with menstrual dysfunction, indicating that meal timing and psychological stress may be sufficient to impair reproductive function.

Insights from Animal Models

Controlled feeding studies in rodents offer valuable mechanistic insights. In a study by Fujiwara et al. (2019), female rats were fed either during their active (night) phase or inactive (day) phase, while consuming the same number of calories.

Rats fed during their inactive phase showed impaired ovarian function, including fewer corpora lutea and reduced ovulatory efficiency. These findings isolate circadian misalignment—independent of caloric intake—as a key factor disrupting reproduction [2].

Evidence from Human Studies

• A study by Fujiwara et al. (2020) evaluated over 3,000 Japanese college students and found that habitual breakfast skipping was associated with increased rates of menstrual irregularities, dysmenorrhea (painful menstrual cycles), and mood symptoms. This is one of the largest observational studies to link breakfast habits with menstrual outcomes, supporting the hypothesis that circadian disruption contributes to reproductive hormone imbalance [3].

• Earlier, Schweiger et al. (1992) compared women with high and low dietary restraint. Despite similar body weights, the high-restraint group had significantly lower mid-luteal progesterone levels, shorter luteal phases, and more anovulatory cycles. This underscores that reproductive dysfunction can occur even in the absence of weight loss or clinical eating disorders.

• A meta-analysis of 78,000 students found that skipping breakfast was among several lifestyle factors significantly associated with primary dysmenorrhea. Other risk factors included stress, poor sleep, low physical activity, and exposure to cold. These findings suggest that reproductive symptoms such as menstrual pain may be modifiable through lifestyle, including the timing and consistency of meals.

Intermittent Fasting and Hormonal Health in PCOS

Intermittent fasting (IF), particularly time-restricted eating (TRE), has gained popularity for metabolic health, but its effects on reproduction are mixed.

A 2022 review by Cienfuegos et al. synthesized human trials examining IF’s impact on sex hormones.

• In women with obesity or PCOS, early TRE (eating between 8 am and 4 pm) reduced total and free testosterone levels and increased sex hormone-binding globulin (SHBG), which may improve symptoms of hyperandrogenism and ovulatory function [3].

• In contrast, late TRE (e.g., eating from 12 pm to 8 pm), which often involves skipping breakfast, did not confer the same hormonal benefits. This reinforces the idea that front-loading energy intake aligns better with circadian physiology and may be more effective for reproductive support, particularly in PCOS.

Knowledge Gaps and Future Directions

• Most evidence comes from observational studies or short-term animal trials. There are very few randomized controlled trials examining the effects of breakfast skipping or intermittent fasting on ovulation, hormone levels, or fertility outcomes in humans

  
  

• Limited Diversity: Most human studies have been conducted in young, healthy, cisgender women, a lot of the times from schools or universities

  
  

• Outdated Studies: Foundational human research, such as the Schweiger study, is over 30 years old. While still relevant, updated methodologies and larger sample sizes are needed to confirm these early findings.

Recommendations include:

• Promote regular breakfast intake. Eating within 1–2 hours of waking may support circadian alignment and stabilize hormonal rhythms

  
  

• Caution with fasting protocols, For individuals with hypothalamic amenorrhea, disordered eating history, or high stress, fasting—even with adequate calories—can worsen hormonal suppression

  
  

• Tailor early TRE for PCOSIn carefully selected clients, early TRE (e.g., 8 am–4 pm) may improve androgen levels and menstrual symptoms, though close monitoring is essential

  
  

Conclusion

Meal timing plays a meaningful role in reproductive hormone regulation via both circadian and metabolic pathways. While more research is needed to establish definitive guidelines, current evidence suggests that aligning food intake with biological rhythms—especially prioritizing earlier meals—may support ovulatory function and menstrual health.

For dietitians, this adds an important dimension to the nutrition care plan, particularly for individuals struggling with cycle irregularities or hormone-related concerns.

References:

1. Ono, M., Dai, Y., Fujiwara, T., et al. (2025). Influence of lifestyle and the circadian clock on reproduction. Reproductive Medicine and Biology, 24:e12641.

   
   

2. Fujiwara, T., Nakata, R., Ono, M., et al. (2019). Time restriction of food intake during the circadian cycle is a possible regulator of reproductive function in postadolescent female rats. Current Developments in Nutrition, 3(12), nzy093.

   
   

3. Cienfuegos, S., et al. (2022). Effects of intermittent fasting on reproductive hormones in women with obesity and PCOS: A review. Nutrients, 14(10), 2343.

   
   

4. Kazama, M., Maruyama, K., & Honda, S. (2022). The association between lifestyle factors and primary dysmenorrhea: A meta-analysis. Value in Health Regional Issues, 29, 94-101.

   
   

5. Fujiwara, T., Nakata, R., Kawamura, T., Yamazaki, A., & Ono, M. (2020). Skipping breakfast is associated with reproductive dysfunction in young women. Appetite, 152, 104602.

   
   

6. Schweiger, U., Laessle, R. G., & Pirke, K. M. (1992). Increased cortisol secretion in restrained eaters. The Journal of Clinical Endocrinology & Metabolism, 75(3), 664–668.