Fasting When Trying to Conceive: Safety and Timing Guide

Quick Answer: Moderate intermittent fasting may be compatible with trying to conceive — particularly for women with PCOS, insulin resistance, or overweight. However, aggressive fasting protocols are not recommended during active conception attempts. Prioritize nutrient density, maintain adequate calories, and stop fasting entirely if pregnancy is confirmed.

Medical Disclaimer: This article is for informational purposes only and does not constitute medical or reproductive advice. If you are actively trying to conceive, consult your OB-GYN or reproductive endocrinologist before making dietary changes.

Should You Fast While Trying to Conceive?

This is one of the more nuanced questions in fasting research because "trying to conceive" (TTC) covers a wide range of situations:

• A metabolically healthy woman in her 20s who wants to lose a few pounds before pregnancy
• A woman with PCOS who needs to improve her hormonal profile to ovulate regularly
• A couple dealing with unexplained infertility under specialist care
• A woman over 35 with limited time who wants to maximize her chances quickly

The appropriate approach to fasting differs significantly across these scenarios. There is no single answer that applies to all TTC situations.

What we can say with confidence:

1. Metabolic health matters for fertility — and fasting can improve it
2. Energy availability also matters — and fasting can impair it if done incorrectly
3. The preconception period sets the nutritional foundation for early pregnancy
4. Once a pregnancy is confirmed, fasting should stop

How Metabolism and Fertility Intersect

Fertility — particularly female fertility — is deeply connected to metabolic health. The body requires adequate energy and optimal hormonal signaling to support ovulation, implantation, and early embryo development.

Insulin resistance and ovulation Insulin resistance is a recognized feature of PCOS, and women with PCOS often have irregular or absent ovulation. The international PCOS guideline puts healthy eating and regular activity first for everyone with the condition, with 5 to 10 percent weight loss a reasonable six-month target for those carrying excess weight (Teede et al., 2018). Whether fasting adds anything beyond the weight loss itself has not been established.

Body weight and reproductive hormones Both underweight and overweight body states impair fertility through hormonal disruption:

• Overweight/obesity: A large cohort study of time to pregnancy found reduced fecundity in overweight and obese women — and the reduction persisted in women whose menstrual cycles were regular, so it is not simply a matter of missed ovulation (Gesink Law et al., 2007)
• Underweight/energy deficit: Weight loss, low body weight, and heavy exercise can shut down the reproductive axis. The Endocrine Society calls this functional hypothalamic amenorrhea (Gordon et al., 2017)

A BMI in the healthy range (18.5–24.9) is associated with better fertility outcomes than the categories on either side of it, though individual variation is significant.

Fasting Approaches Compatible With TTC

Approach 1: Overnight 12-hour fast The most conservative and broadly compatible option. Simply eating dinner by 7–8pm and not eating again until 7–8am is close to what many people already do overnight, and is unlikely to place meaningful stress on the reproductive axis. This is appropriate for virtually all women TTC unless their physician advises otherwise.

Approach 2: 14:10 fasting A 10-hour eating window (e.g., 9am–7pm) is a moderate approach with reasonable evidence for metabolic benefit. For most women who are not underweight and are eating sufficient calories, this is unlikely to impair fertility.

Approach 3: 16:8 for metabolic optimization (PCOS, insulin resistance) For women with PCOS or significant insulin resistance who need metabolic improvement to restore ovulatory cycles, a 16:8 protocol may be medically justified. The direct evidence is thin: a single-arm study of 15 women with anovulatory PCOS found five weeks of eight-hour time-restricted feeding improved menstrual regularity in 11 of them, alongside falls in testosterone and insulin resistance — but there was no control group and no ovulation confirmed by pregnancy (Li et al., 2021). This should ideally be done with the knowledge and support of a reproductive endocrinologist or dietitian.

Not recommended while actively TTC:

• 18:6 or OMAD (one meal a day) — overly restricts eating opportunity and increases risk of nutrient insufficiency
• Extended fasting (24+ hours) — not appropriate during preconception period
• Any protocol that results in significant caloric deficit

The Preconception Nutrition Priority

The preconception period — ideally 3–6 months before attempting conception — is when nutritional foundations are most critical. During this time:

Folate must be adequate. The neural tube forms in the first weeks of pregnancy — often before a woman knows she is pregnant. WHO advises 400 μg of folic acid daily from the moment you begin trying to conceive until 12 weeks of gestation. Supplemental folic acid has also been consistently linked to less infertility and less pregnancy loss (Gaskins & Chavarro, 2018). Compressed eating windows should not compromise folate-rich foods (dark leafy greens, legumes, fortified foods) or folic acid supplementation.

Iron stores need to be adequate. Pregnancy raises iron requirements sharply. Women who restrict eating should pay careful attention to iron-rich foods (lean red meat, legumes, leafy greens) and consider having ferritin levels checked.

Omega-3s, iodine, choline should be prioritized during eating windows if fasting. Long-chain omega-3s in particular have been linked to better female fertility. Vitamin D is the exception worth naming: outside of actual deficiency it shows no clear fertility benefit, so treat it as general health rather than a fertility lever (Gaskins & Chavarro, 2018).

When evaluating whether your eating window allows adequate nutrient intake, this list of preconception nutrients is the benchmark. If you can't reliably meet needs in your eating window, widen the window.

During the Two-Week Wait (TWW)

The period between ovulation and expected period (the "two-week wait") is a time when implantation is occurring if conception has happened. During this time:

• Maintain the same conservative approach as during the broader TTC period
• Do not begin new, more aggressive fasting protocols during the TWW
• Ensure adequate caloric and nutritional intake

If a pregnancy test is positive, stop intermittent fasting. Deliberate fasting in pregnancy has not been shown to be safe, and energy and nutrient needs rise as pregnancy goes on.

For Men Trying to Conceive

Male partners often overlook preconception nutrition. For men:

• Moderate fasting (16:8) is generally compatible with TTC preparation
• Eat well rather than chase single nutrients. A Cochrane review of 12 small and medium trials found antioxidant supplements in subfertile men may improve live birth rates, but rated that very low certainty and could not say which nutrients or doses were doing the work (de Ligny et al., 2022; Gaskins & Chavarro, 2018)
• Avoid extreme caloric restriction
• Maintain adequate protein intake (a compressed eating window can make protein targets harder to hit)

See our article on fasting and fertility for detailed information on male and female mechanisms.

Practical Recommendations

If you have PCOS or insulin resistance and are TTC:

• Work with your reproductive endocrinologist and a registered dietitian
• A 14:10 or 16:8 window earlier in the day may support insulin sensitivity and more regular ovulation
• Track your cycles carefully (basal body temperature, OPK strips) to confirm ovulation is occurring

If you are metabolically healthy and TTC:

• A 12-hour overnight fast is appropriate and safe
• Consider widening to 14 hours maximum only if comfortable and eating enough
• Focus most of your energy on nutritional density rather than fasting duration

If you are underweight or have a history of eating disorders:

• Do not fast during TTC
• Focus on achieving and maintaining a healthy weight and nutritional status
• Work with a healthcare provider specializing in eating disorders and reproductive health

When to stop fasting:

• Positive pregnancy test — stop fasting immediately
• Irregular menstrual cycles after starting fasting — reduce or stop fasting
• Three or more months of trying without success — reassess dietary approach with your physician

Frequently Asked Questions

Is it safe to fast during the luteal phase (second half of the cycle)?

Many practitioners recommend reducing fasting stringency during the luteal phase (post-ovulation). Women do tend to eat more then: across 29 ovulatory cycles, energy intake ran about 300 kcal/day higher in the luteal phase than the follicular phase (Barr et al., 1995). That is measured intake, not a measured requirement — studies of resting energy expenditure find much smaller differences. If you experience luteal phase symptoms (mood changes, cravings, fatigue) while fasting, consider shifting to a 12-hour fast only during this time.

Can fasting help me lose weight before getting pregnant?

For women who want to lose weight before conceiving, a moderate fasting approach (14:10 or 16:8) combined with balanced nutrition is reasonable. Weight is worth addressing for its own sake: a large cohort study found overweight and obese women took longer to conceive (Gesink Law et al., 2007). Give your cycles time to settle before you start trying.

Does fasting affect the quality of my eggs?

There is no direct human evidence that moderate intermittent fasting affects egg quality positively or negatively. In practice, maintaining nutritional adequacy is the priority.

Should I tell my doctor I'm fasting while TTC?

Yes. Your reproductive endocrinologist or OB-GYN should know about your dietary approach so they can give appropriate guidance, monitor hormonal markers, and adjust recommendations as needed.

Citations

1. Teede HJ, et al. Recommendations from the international evidence-based guideline for the assessment and management of polycystic ovary syndrome. Fertil Steril. 2018;110(3):364–379.
2. Gordon CM, et al. Functional hypothalamic amenorrhea: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2017;102(5):1413–1439.
3. Gesink Law DC, et al. Obesity and time to pregnancy. Hum Reprod. 2007;22(2):414–420.
4. Gaskins AJ, Chavarro JE. Diet and fertility: a review. Am J Obstet Gynecol. 2018;218(4):379–389.
5. World Health Organization. Periconceptional folic acid supplementation to prevent neural tube defects. https://www.who.int/tools/elena/interventions/folate-periconceptional
6. Li C, 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.
7. de Ligny W, et al. Antioxidants for male subfertility. Cochrane Database Syst Rev. 2022;5(5):CD007411.
8. Barr SI, Janelle KC, Prior JC. Energy intakes are higher during the luteal phase of ovulatory menstrual cycles. Am J Clin Nutr. 1995;61(1):39–43.