Diet & female fertility: doctor, what should I eat (Chiu et al, 2018), is an excellent paper that reviewed the available research (171 references) on dietary factors affecting human fecundity (the capacity to produce offspring).
They concluded:
- Although much work remains, current evidence has accrued to support that diet could be a modifiable factor for female fecundity
- According to existing data, intake of a folic acid supplement before and during pregnancy not only prevents birth defects, but also maintains pregnancy success
- Despite encouraging data in animal studies, little evidence supports beneficial effects of vitamin D on human fertility, unless there is a proven deficiency
- There is considerable evidence suggesting that greater intake of u-3 PUFA and lower intake of trans fats are associated with shorter time to pregnancy and better ART outcomes, whereas the effect from other fatty acids (such as u-6 PUFA, SFA, and MUFA) on female fecundity is less clear
- Studies generally suggest that soy appears to have no harm on female fertility, and little data is available to disentangle the relationship of dairy, meat, and fish intake, environmental contaminants, and reproductive outcomes
- Finally, greater adherence to healthy dietary patterns favouring whole grains, fish, fruits, vegetables, and olive oils may not only improve overall health but boost fecundity
Keep reading to see the authors individual recommendations and for information about how diet can affect sperm see ‘Diet is a modifiable male factor for semen quality‘.
Vitamin B9
Folate (natural form vitamin B9 / folic acid synthetic form), is involved in the synthesis of DNA, crucial in egg & sperm production, fertilisation, and pregnancy. A daily supplement containing 0.4–0.8 mg folic acid is recommended to prevent neural tube defects.
The EARTH study compared women taking >0.8 mg/d & <0.4 mg/d folate, before conception. Findings: higher serum levels of folate measured during the stimulation phase were associated with a higher probability of live birth.
Vitamin D
Vit D receptors are distributed across the reproductive system, including ovaries, uterus, and endometrium. It stimulates ovarian steroidogenesis, promotes follicular maturation, and regulates HOXA10 expression (involved in successful implantation), and its deficiency may be involved in the pathogenesis of polycystic ovary syndrome (PCOS).
Animal studies have shown that Vit D deficient female rodents have reduced fertility, but results in humans are inconsistent. This may be because Vit D only helps if there is a known deficiency, therefore check the levels first, to establish the correct level of supplementation
Carbohydrates
Both quality and quantity of dietary carbohydrates influence glucose homeostasis and insulin sensitivity, which influences ovarian androgen production and ovarian function.
Whole grains and constituents of whole grains (including phytic acid, vitamins, and selenium), have antioxidant anti-inflammatory properties and beneficial effects on glucose metabolism, which may boost fertility because insulin resistance and oxidative damage have been implicated in subfertility. Also, Lignan, the hormonally active compound in whole grains, through its pro-estrogenic and anti-estrogenic effects, may exert reproductive benefits. The EARTH study showed that higher preconception intake of whole grain was associated with higher probability of live birth.
Fatty Acids
Fatty acids are used as energy substrates during egg maturation & early embryo development. They are critical precursors for a variety of substrates e.g. prostaglandins and steroid hormones, which play a vital role in implantation and pregnancy maintenance.
The Biocycle study showed increased long-chain polyunsaturated fatty acid (PUFA) intake was associated with increased luteal progesterone concentration, increased total E2 and lower risk of anovulation & endometriosis. PUFA is also associated with decreased serum FSH levels in normal-weight but not in obese women with normal ovarian reserve & may delay ovarian aging.
The EARTH study reported that for every 1% increase in serum long-chain u-3 PUFA levels, the probability of clinical pregnancy and live birth increased by 8%. In another study, higher preconception PUFA intake was associated with better embryo morphology.
Protein
Recommendations on protein intake (amount and type) for women undergoing fertility treatments do not exist, and the controversy surrounding the evidence on animal and dairy protein as well as soy and phytoestrogens remains.
Concerns are because of the potential contamination of dietary protein sources by pesticides and endocrine-disrupting chemicals & the presence in them of measurable amounts of steroid hormones and growth factors that when absorbed may alter reproductive outcomes.
Dairy
Studies regarding dairy intake are inconclusive.
One showed in human populations with higher per-capita consumption of milk, the decline in fertility with aging was steeper and fertility at older ages was lower. Similarly, higher dairy protein intake, and not total protein intake, was associated with lower ovarian antral follicle counts among women presenting for infertility treatment.
Others have shown dairy and milk consumption was associated with increased fecundability & positively associated with live birth only among women older than 35 years of age. The observed association did not differ between full-fat and low-fat dairy foods and did not appear to be driven by one single dairy food item
Dietary Patterns & Reproductive / ART Outcomes
A higher frequency of fast food and lower frequency of fruit and vegetables intake is related to longer time to pregnancy.
Adherence to a ‘‘fertility diet’’ (consisting of high consumption of monounsaturated fat, vegetable protein, high-fat dairy, low-glycaemic carbohydrates, multivitamins, and iron from plants and supplements) was associated with a lower risk of ovulatory infertility. In Spain, women with the highest adherence to the Mediterranean diet (characterized by high consumption of fruits and vegetables, fish and poultry, low fat products, and olive oil) had lower odds of experiencing difficulties getting pregnant.
A favourable role of healthy dietary patterns on ART outcomes has been reported. High intake of whole grains, fruits, vegetables, monounsaturated or polyunsaturated oils, meat or meat replacers, and fish before conception was associated with higher probability of ongoing pregnancy.
A maternal Mediterranean diet (high intake of vegetables and vegetable oils, fish, and legumes, low snack intake) but not ‘‘health conscious/low processed’’ diet (high intake of fruits, vegetables, legumes, whole grains, and fish, low intake of mayonnaise, snacks, and meat products) was associated with higher probability of pregnancy. Given that high intake of vegetable oil was dominant in the Mediterranean diet but not in the ‘‘health conscious/low processed’’ diet, these findings suggest that nutrients in vegetable oil, such as Lineic Acid, may be responsible for this association. Similarly, in a recent study of young non-obese Greek women, a similar effect of adherence to Mediterranean dietary patterns and ART success was noted
EMERGING CONCERNS
Foods are vehicles for delivering nutrients as well as non-nutritive constituent chemicals, which could be due to naturally occurring contaminants in the environment or artificially introduced during the processing, packaging, preparing, storage, and transportation of food. Well known examples include mercury in fish, pesticide residues in produce, and growth hormones, antibiotics, and polybrominated diphenyl ethers in meat.
Emerging research has suggested that nutrients may interact with the toxicant in affecting specific health outcomes and vice versa. For example, in both human and nonhuman studies, intake of soy food and folates was found to be protective against the adverse reproductive effects of bisphenol-A. A recent study has shown that the presence of high pesticide residues in fruits and vegetables might modify the beneficial effects of fruits and vegetables on reproductive success. Because environmental contaminants are widely dispersed, future studies may need to consider exposure to environmental contaminants (and mixtures of these contaminants) when investigating the associations between food/nutrients and health outcomes to better form dietary recommendations and guide action for general and susceptible populations
