Traditionally the main focus of nutrition and fertility has been on weight management, restoring ovulation function, and lifestyle factors such as quitting smoking and reducing alcohol intake. While the positive impact of these changes has been documented, there is emerging evidence to suggest that specific dietary strategies can optimise egg and sperm quality. Nutrition can also influence health conditions in females that affect fertility. As one in six heterosexual couples in Ireland may experience infertility,1 it is essential that health professionals are aware of how nutrition can impact fertility. It is also important that they understand the Fertility Dietitian’s role in assessing and managing nutrition and lifestyle factors that affect fertility.
Written by Jemma Henry, CORU Registered Dietitian, MINDI, Certified Fertility and Prenatal Dietitian, Post Graduate Diploma in Nutrition and Dietetics, BSC Biochemistry and Molecular Biology and Diploma in Food Science
jemmahenry@nourishmyfertility.ie
Age, health conditions, mechanical issues e.g. blocked tubes, smoking, diet, obesity, and endocrine disruptors are all factors that can affect female fertility. By identifying the modifiable factors that can be influenced by nutrition and lifestyle changes, the impact of these factors can be modulated to optimise fertility.
The key objectives that a Fertility Dietitian will focus on to support a woman’s fertility are optimising egg health, restoring ovulation, reducing inflammation, reducing oxidative stress, managing existing health conditions and improving the overall nutritional adequacy to support fertility and potential pregnancy. Knowing which objective is a priority and which dietary strategies to use are key considerations for the Fertility Dietitian. Optimising egg health is particularly important as age is a major factor affecting female fertility.2 As a woman ages, an increased percentage of eggs contain genetic abnormalities and older eggs are likely to accumulate more DNA errors.3 Oxidative stress — an imbalance between reactive oxygen species (ROS) and protective antioxidants — is associated with reduced oocyte and embryo quality.4,5
As males are found to be solely responsible for 20–30 percent of infertility cases and contribute to 50 percent of cases overall, it is vital that they are considered when advising nutrition and lifestyle changes.6 An accumulation of evidence shows that oxidative stress also plays a role in male infertility. The sperm membranes contain a large amount of long-chain polyunsaturated fatty acids, making them highly susceptible to oxidation.7 This can lead to an increased risk of DNA fragmentation and further impairments to sperm quality.8 Diet and lifestyle strategies to reduce oxidative stress are also important factors for the Fertility Dietitian to consider when aiming to optimise sperm health.
Nutritional Factors
Nutritional considerations when reducing oxidative stress include increasing antioxidants and anti-inflammatory omega-3 fatty acids to counteract the adverse effects of oxidative stress. The question continues to arise whether there is an actual fertility diet. Currently, there is not enough evidence to determine an official ‘fertility diet’. Literature suggests that there are certain dietary patterns or strategies that can optimise fertility.9,10 These dietary patterns are associated with a Mediterranean-style diet which has been characterised by a high consumption of wholegrains, vegetables (including pulses), fruits, unrefined carbohydrates, olive oil, oily fish and with a low consumption of red meat.9 This diet pattern is in stark contrast to the western diet which is characterised by saturated fat, refined carbohydrates, processed meat and low levels of vitamins and minerals.9 The western diet is considered to be pro-inflammatory as it is associated with higher levels of inflammation which has been proposed to be related to poor fertility outcomes in both men and women.10 The dietary principles that are associated with the Mediterranean diet have also demonstrated associations with a lower risk of ovulatory fertility and a reduced risk of infertility.11 Studies have shown positive associations between the Mediterranean diet and improvements in Assisted Reproductive Technology (ART) outcomes such as higher embryo yield and the increased probability of achieving pregnancy.12,13 Other diets have been investigated for improvements in fertility in the context of ART and unsurprisingly they share similar dietary patterns to the Mediterranean diet such as emphasising fruit, vegetables, wholegrains, fish and polyunsaturated fatty acids (PUFA) while limiting processed foods.14,15 Although the effect of dietary patterns on pregnancy outcomes in people using ART is still inconclusive, these studies show promise as potential strategies to improve ART-assisted outcomes.16 Healthy eating patterns have also demonstrated a beneficial effect on sperm parameters.17
The Fertility Dietitian will help individuals choose carbohydrates based on their food preferences while considering the glycaemic index (GI) and glycaemic load (GL) of the carbohydrates. The GI is the relative ranking of carbohydrates based on how a carbohydrate affects blood sugar. Carbohydrates that have a low GI rating will have less of an impact on blood sugar than those with a high GI rating. The Glycaemic load (GL) is a more accurate way to assess the effect of diet on blood glucose concentration because it accounts for carbohydrate quality through the GI and carbohydrate quantity through portion size.18 Studies have shown, that a higher dietary GL was associated with an increased risk of infertility due to anovulation and reduced fecundity (the ability to produce offspring) in women.18,19 The impact of high glycaemic foods has been also shown to impact sperm quality.20
The type of protein appears to be important regarding ovulatory infertility as Chavarro et al found that replacing animal protein with vegetable protein reduced the risk of infertility due to anovulation.21
Another nutritional consideration that the Fertility Dietitian will include in their nutritional assessment is ensuring that the client is receiving 400 µg of folic acid to prevent neural tube defects (NTDs).22 This dosage can be higher if they have been medically assessed to have increased requirements, for example, previous NTDs, malabsorption disorders, or obesity. Interestingly, there is growing evidence that folic acid could also improve other reproductive outcomes including promoting oocyte quality.23
Vitamin D is thought to play an important role in fertility as receptors are found in the ovaries, endometrium, placenta, pituitary gland, and sperm and testicles.24 Observational studies show that vitamin D deficiency is a risk marker for reduced fertility but is still not clear whether vitamin D supplement improves fertility.25 In the case of vitamin D deficiency during infertility treatment, vitamin D supplementation may benefit women with disorders like polycystic ovary syndrome, insulin resistance, or low antimullerian hormone levels.26 Vitamin D deficiency and insufficiency are also associated with poorer ART outcomes in women.27
Currently, there is no specific recommendation for Vitamin D in Ireland for women trying to conceive. The EFSA has very recently updated its guidance to advise that 12-65-year-olds should supplement 15 µg (600 IU) of Vitamin D for the winter months or daily if individuals are of darkerskinned ethnicity or pregnant.67 Other authors have suggested higher levels of Vitamin D for those trying to conceive.25
Dietary strategies will also focus on increasing foods that contain nutrients such as Zinc, Iron, and B12. Zinc is involved in spermatogenesis, ovulation, and oocyte maturation while iron deficiency is associated with ovulatory infertility.28-30 Vitamin B12 deficiency individually and in combination with hyperhomocysteinemia is associated with early pregnancy loss.31
In practice, the Fertility Dietitian will encourage monounsaturated and polyunsaturated fats while reducing trans and saturated fat. The rationale for this is based on observational studies that have shown a higher amount of trans fats is associated with a higher risk of ovulatory infertility and reduced fecundability.32-33 Omega 3 fatty acids are essential fatty acids, that have a significant antiinflammatory effect.34 These have been associated with a higher probability of clinical pregnancy and live birth in women undergoing infertility treatment with ART.35 Most recently a systematic review summarised the emerging association between omega-3 intake through diet and favourable IVF/ICSI outcomes, possibly via its effect on egg quality.36
Caffeine and alcohol are also other important factors to consider as part of the nutritional assessment. The European Food Safety Authority guidelines advise women who are trying to conceive or are pregnant to keep caffeine intake below 200 mg to reduce negative pregnancy outcomes.37 While increased caffeine consumption is associated with spontaneous abortion and (>500mg per day) may affect time to pregnancy, there is a lack of evidence to show that there is an association between caffeine and fecundity or caffeine and IVF/ICSI outcomes.38-41 The HSE advises women who are trying to conceive to aim to avoid alcohol but to what extent alcohol consumption affects female fertility remains unclear.42 Female alcohol consumption is associated with reduced fecundability and another study also suggested that modest drinking levels may decrease fecundability if consumed during critical physiologic intervals of the menstrual cycle.43,44 Drinking more than 84g of alcohol per week (1 alcoholic beverage=12g of alcohol) was associated with reduced IVF/ ICSI outcomes in both men and women.41 While there are studies showing how alcohol affects sperm quality in heavy drinkers there is little evidence to demonstrate alcohol’s effect on fecundability in the male.45,46
As well as looking at lifestyle factors such as smoking, reducing exposure to endocrine disruptors is also a significant part of the advice given by the Fertility Dietitian. Endocrine Disrupting Chemicals (EDCs) are ubiquitous exogenous substances that can mimic or interfere with the endocrine system. Examples of EDCs include bisphenol A, phthalates, pesticides, and pollutants such as dioxin and polychlorinated biphenyls (endocrine society) The main way humans are exposed to them is through diet. EDCs can affect conception, in-utero development, neonatal life, and long-term child and maternal health by affecting both male and female reproductive processes. Complete avoidance is impossible, but dietary alterations such as avoiding plastic bottles and packaging have been shown to reduce exposure.47
Health conditions impacted by nutrition
In support of how important nutrition’s role is in managing female infertility, Kumar et al have proposed a self-administered screening tool to identify women that would benefit from nutritional intervention to improve fertility. This screening tool is awaiting validation. This publication also summarises health conditions such as Polycystic ovary syndrome (PCOS), Endometriosis and being over/underweight as health conditions that can be nutritionally optimised to improve female fertility.48
PCOS is the most common endocrine disorder in women of reproductive age. It is the leading cause of anovulatory infertility.49 The key role of dietary intervention with PCOS is to restore ovulation, restore menstrual cycle regularity, reduce insulin resistance and reduce weight if necessary. While lifestyle management is recommended as first-line treatment of PCOS, the optimal dietary composition is unclear.50 Focusing on low GI food is one of the approaches the Fertility Dietitian will use to reduce insulin resistance and restore menstrual regularity.51 As there is a high prevalence of women in this PCOS population that are obese or overweight, research suggests that approximately 5 percent of weight reduction is adequate to improve insulin resistance, high levels of androgens, reproductive system dysfunctions, and fertility in overweight women with PCOS.50 Endometriosis is an oestrogendependent, chronic inflammatory disease affecting up to 10 percent of women of reproductive age.52,53 It is also a systemic condition and has been found on virtually all organs.54 Some women with Endometriosis are asymptomatic, while for others, it is a debilitating condition that can cause pain and infertility.55 The pathophysiology of infertility in mild cases of Endometriosis is not understood but it has been associated with anatomical disturbances in severe cases.54 It has also been linked to a negative impact on egg quality.53 As Endometriosis is an inflammatory condition, dietary approaches often include focusing on foods with anti-inflammatory properties such as omega 3 fatty acids and antioxidants from fruit and vegetables, herbs/spices that contain polyphenols/ flavonoids and reducing processed food.56 While the research suggests that increased consumption of omega-3 has a positive effect on Endometriosis the overall evidence for using an an-inflammatory approach remains unclear.57 Higher amounts of red meat, alcohol and trans fats are associated with an increased risk of Endometriosis.58-60 Part of the Fertility Dietitian’s role in this area of Endometriosis is symptom management. Visceral hypersensitivity is a key feature in both Irritable Bowel Syndrome (IBS) and Endometriosis and may explain why they share similar symptoms.61 A low FODMAP diet which has been investigated for its effectiveness for individuals with IBS may be an effective dietary strategy for women with gut symptoms and Endometriosis.62,61
A significant association between IBS, Eating Disorders (ED), and Endometriosis was demonstrated in the ENDONUT trial where the prevalence of IBS and ED in women with Endometriosis was higher than in the general population.63 This has further implications for the dietary strategy used by the Fertility Dietitian as they will have to also consider an individual’s relationship with food while achieving nutritional adequacy to support a potential pregnancy. Weight management is also an important consideration for the Fertility Dietitian when trying to optimise fertility. Obesity is a known risk-factor for infertility. It has been shown to affect ovulatory function, time to conception and is associated with poor reproductive outcomes in assisted conception.64,65 However there is insufficient evidence to suggest that short-term weight loss before ART improves outcomes.67 National Clinical Guidelines advise maintaining a BMI of 19-25 kg/m2 as part of recurrent miscarriage management advice.66 Low body weight can also affect fertility by impacting ovulation while increasing body weight may improve the chance of conception.64
Conclusion
Although questions still remain unanswered it is clear that nutrition and lifestyle play a critical role in impacting both male and female fertility. While we do not have an official fertility diet, there are dietary patterns/ strategies that can positively affect fertility. Highquality intervention studies are warranted to confirm these dietary patterns/ strategies with a view to developing dietary guidelines that go beyond the traditional advice of weight management, alcohol, and smoking.
As there is an abundance of misinformation on this topic on infertility forums, the internet, social media and from non-qualified practitioners, individuals struggling with infertility are trying diets and supplements which may further reduce their chances of conception and add to an already costly ART journey.
As nutrition and lifestyle factors are modifiable, it is vital that they are part of the infertility management treatment plan for both men and women. This nutrition and lifestyle advice should be given as a consultation to allow for a full nutritional assessment. The appropriate dietary patterns/ strategies and their rationale should be explained to the individual. Furthermore, the level of evidence underpinning each diet strategy discussed should also be explained in an easyto-understand manner. This will allow the individual to make an informed decision about their nutritional and lifestyle choices which may be impacting their fertility. This will undoubtedly reduce the use of alternative diets and non-evidenced-based supplements that are currently being widely used by men and women experiencing infertility. It is the unique skill set of the Fertility Dietitian that allows them to assess the available evidence and to determine the most appropriate nutritional plan in order to optimise fertility. The Fertility Dietitian is perfectly placed to be an integral part of the multidisciplinary team for infertility management.
References on request
