Dietary Patterns to Improve Fertility Parameters in Women and Men

Abstract

Infertility impacts the lives of many individuals worldwide. More couples are waiting to have children until later in life, which affects their chances of ever having a family. There may also be a relationship between unhealthy diets and declining fertility in industrialized countries. In recent years, most nutritional studies have focused on the effect of individual micronutrients or antioxidants on fertility, rather than examining dietary patterns. Such studies have produced inconsistent results and it is important to recognize the synergistic relationship between nutritional components. The concept of a “fertility diet” has remained elusive, yet dietary approaches could function as non-invasive and natural methods for treating infertility. The purpose of this literature review is to compare the most current research studies in order to determine what dietary patterns may improve fertility parameters in women and men. For this review, the researcher analyzed 22 free full text and peer-reviewed original research studies published within the last ten years that sought to establish an association between diet and fertility in women and/or men. About 77% of the studies analyzed found a positive correlation between healthy dietary patterns and reproductive wellness. Dietary patterns such as the Mediterranean diet (MedD) and the Prudent diet do not appear to worsen fertility status, although studies have found that unhealthy diets (i.e. the Western diet) may negatively affect fertility. Dietary approaches may improve the chances of conception and should be a central component of fertility counseling.

Introduction

Infertility is defined as the inability to conceive after one year of unprotected sex and it affects an estimated 186 million people worldwide (Fontana & Della Torre, 2016). When the woman is over 35 years of age, infertility is usually diagnosed after only six months of trying to conceive. More couples are waiting to have children until later in life, which reduces their chances of ever having a family. About 20% of women wait until after age 35 to have children, when the risk of infertility increases dramatically (Pizzorno & Murray, 2013). There may also be a relationship between unhealthy diets and declining fertility in industrialized countries. Globally, dietary behavior is shifting and unhealthy diets are increasingly common in men and women of reproductive age (Jurewicz et al., 2018). It is possible that the “Western Diet,” characterized by low intakes of fruits and vegetables and high intakes of saturated fat and sugar, may be negatively affecting the health and fertility of couples worldwide. 

There are many different pathological causes of male and female infertility. Female infertility can be caused by diminished ovarian reserve, polycystic ovary syndrome (PCOS), tubal obstruction, or endometriosis (Pizzorno & Murray, 2013). Male infertility usually stems from abnormal sperm concentration, count, morphology, or motility. Age is also a significant risk factor for both female and male fertility; optimal ages for reproduction generally range from 18 to 35 years for females and 16 to 40 years for males. When the results of an infertility evaluation are normal and no apparent causes can be found, practitioners assign a diagnosis of unexplained infertility (Quaas & Dokras, 2008). Infertility affects men and women more or less equally; about one third of cases stem from male causes, one third from female causes, and one third from joint issues. 

Regardless of modern advances in assisted reproductive technologies (ART), infertility rates have remained high worldwide and it is crucial to consider modifiable risk factors to help couples achieve natural conception. In vitro fertilization (IVF) is the most common and effective type of ART. IVF has one of the highest success rates for therapeutic options for infertile couples, however it can be expensive and involve a long preparation time (Djaali et al., 2019). There are many other potential risks of IVF, which alternative therapies may help bypass. These risks include psychological distress, operative complications, multiple gestations, and ovarian hyperstimulation syndrome (Shahin et al., 2008). IVF also involves a significant financial commitment. The treatment is often not covered by insurance plans and a single IVF treatment can range from $12,000-$17,000 (In Vitro Fertilization, n.d.). Finally, fertility treatments can cause a great deal of psychological stress, affecting a couple's quality of life and causing anxiety and/or depression.

In recent years, most nutritional studies have focused on the effect of individual micronutrients or antioxidants on fertility, rather than examining dietary patterns (Jurewicz et al., 2018). Such studies have produced inconsistent results. This could be due to ignoring the synergistic relationship between nutritional components (Danielewicz et al., 2018). There is a complex connection between diet and disease, and while there are many ideas about various foods and supplements that may improve fertility, it seems that an actual “fertility diet” remains elusive. Dietary approaches may function as non-invasive and natural methods for treating infertility and could be a central component of fertility counseling.

There is evidence that preconception dietary patterns can affect fertility. The Nurses’ Health Study II, for instance, followed the diets and reproductive outcomes of 17,544 women to discover what dietary patterns seemed to improve fertility (Collins & Rossi, 2015). Some general nutritional guidelines that they discovered included: replacing saturated fat with unsaturated, avoiding trans fatty acids, increasing protein intake from plant sources, emphasizing low-glycemic and slow-digested carbohydrates, consuming full-fat dairy products, and increasing iron intake from plant sources. The researchers determined that women who adhered to this diet had a 66% lower risk of ovulatory disorder infertility and a 27% lower risk of infertility from other causes. 

Dietary patterns that may improve fertility are also beneficial for general health in several other ways. For instance, the Mediterranean diet (MedD) has been found to correspond with reduced risk of cancer, cardiovascular disease, neurodegenerative disease, and diabetes (Silvestris et al., 2019). It features high intakes of fruit, vegetables, legumes, nuts, and cereals, with low intakes of dairy products, meat, poultry, and saturated fat. The Dietary Approaches to Stop Hypertension (DASH) diet (marked by high intakes of fruit, vegetables, and low-fat dairy products) has been linked to the prevention and treatment of hypertension, diabetes, obesity, and coronary artery disease (Danielewicz et al., 2019). Finally, the Prudent diet (characterized by high intakes of fish, chicken, fruit, vegetables, legumes, and whole grains) has been associated with lower risk of cardiovascular disease and colorectal cancer in men (Gaskins et al., 2012). 

In addition to these health benefits and potentially improving fertility, these dietary patterns may also benefit both the mother and infant throughout pregnancy and lactation. The MedD, for instance, has been linked to a decreased risk of preterm delivery, gestational diabetes, high birth weight, and obesity development in children (Jardí et al., 2019). Despite these benefits, pregnant and postpartum women do not always follow recommended dietary guidelines. Adherence to lifestyle changes (i.e. diet, weight loss, cessation of smoking, vitamin supplementation, and reduced alcohol intake) is often low among women trying to become pregnant, even if they understand that these changes will increase fertility (Joelsson et al., 2016). Preconception counseling for women of fertile age can help to improve adherence to lifestyle modifications, enhance natural fertility, and prevent pregnancy complications. 

The entire role of nutrition in relation to male and female fertility is not yet complete. A collection of current research studies on nutrition and fertility may help to inspire an effective “fertility diet” for the general public. This could have huge ramifications for the many couples worldwide who struggle to conceive. The purpose of this literature review is to compare the most current research studies in order to determine what dietary patterns may improve fertility parameters in men and women.

Methods

For this literature review, the researcher used the search parameters “dietary pattern,” “Mediterranean diet,” “dietary approaches to stop hypertension,” “prudent diet,” “fruit and vegetable intake,” and (fertility or infertility) in ProQuest, PubMed, Alt HealthWatch, and Directory of Open Access Journals. The search was limited to free full text and peer-reviewed original research studies published within the last ten years that sought to establish an association between dietary patterns and fertility in women and/or men. This review includes the 22 original research studies (twelve female and ten male studies) found within these parameters.

Results

Female Studies

Obesity in women of reproductive age is a risk factor for infertility, pregnancy complications, and adverse offspring outcomes. In a study of 248 healthy women (mean age: 27.5 years), Boghossian et al. (2013) investigated the relationship between MedD adherence and body fat composition. The study defined the MedD as: 

The traditional Mediterranean diet reflects food patterns found in Greece and Southern Italy in the early 1960s, and is characterized by an abundant intake of plant foods (vegetables, legumes, fruits, nuts, cereals) with olive oil as the main source of fat, a high-to-moderate intake of fish, a low-to-moderate consumption of eggs, dairy products (mainly cheese and yogurt) and poultry, a low intake of red meat and a regular but moderate intake of alcohol (mainly wine during meals).

The participants had an average body fat percentage of 29.5%. The researchers found that adherence to the MedD was associated with lower total and regional adiposity. Participants with high MedD adherence had a significantly lower body mass index (BMI) and smaller waist and thigh circumferences at baseline than women with low adherence. The researchers concluded that the MedD could be associated with maintaining a favorable body weight, possibly due to the high consumption of satiating dietary fiber and the overall low energy density of the MedD. Energy density reflects the number of calories in a food in relation to its weight (Low-Energy-Dense Foods, n.d.). A person can consume a larger portion of a low energy density food for the same number of calories. This is why diets such as the MedD may promote weight loss and longterm weight management.

It is hypothesized that the MedD may also affect ART and IVF outcomes. In a study of 244 non-obese women (median age: 35.0 years) undergoing IVF treatment for the first time, Karayiannis et al. (2018) studied the relationship between MedD adherence and IVF performance. The participants completed a food frequency questionnaire (FFQ) and each person was assigned a MedDietScore to rate their level of adherence. Higher adherence to the MedD was found to be associated with greater likelihood of clinical pregnancy and live birth in non-obese women less than 35 years of age. This result was not found in participants 35 years or older. Furthermore, a higher MedDietScore was not related to ovarian stimulation outcomes, embryo quality measures, or implantation. The researchers provided several possible explanations for the beneficial effects of the MedD on reproductive health. For instance, consumption of whole grains could improve fertility and treatment outcomes. Red meat consumption, which is low on the MedD, is believed to have a negative effect on clinical pregnancy rates. The MedD has also been favorably related to glycemic control, which may affect IVF outcomes. The MedD is also characterized by a high intake of beneficial fatty acids from the consumption of extra virgin olive oil in place of saturated fatty acids. Finally, the MedD is rich in antioxidants from fruits and vegetables, which may reduce oxidative stress to the endometrium. 

In another study on the MedD and IVF outcome, Sun et al. (2019) investigated the relationship between dietary patterns and embryo yield among infertile women (mean age: 31.8 years). In this observational prospective cohort study, 590 women completed a FFQ and were grouped together as either higher MedD adherence (n=228) or lower MedD adherence (n=362). Despite similar baseline characteristics between the two groups, the women with higher adherence to the MedD showed a positive correlation with both embryo yield and number of fertilized oocytes. However, implantation rate and clinical pregnancy rate were found to be similar between the two groups. The researchers concluded that greater adherence to the MedD could improve the number of available embryos in the IVF cycle of infertile women. 

Similarly, Vujkovic et al. (2010) followed 161 couples undergoing IVF or intracytoplasmic sperm injection (ICSI) treatment to determine if dietary patterns affected treatment outcomes. Two dietary patterns were identified: “health conscious–low processed’’diet (HCLPD) and MedD. The study found that the MedD increased the chance of pregnancy after IVF/ICSI treatment by about 40%, despite considerable similarities to the HCLPD. Both diets were marked by high intakes of vegetables, fish, and legumes and low intakes of snacks. However, only the MedD was found to increase the chance of pregnancy after IVF/ICSI treatment. The researchers gave two possible reasons for this finding. First, the MedD features much higher intake of vegetable oils, which are rich in linoleic acids, omega-6 fatty acids that are precursors to prostaglandins. Prostaglandins are important for ovulation and maintenance of pregnancy and high intakes of linoleic acid may positively affect implantation. Second, the MedD showed an increase in vitamin B6 in blood and follicular fluid, which is involved in many biochemical pathways and may increase reproductive function. This study provided insight in the important relationship between dietary patterns and IVF/ICSI outcomes, and may highlight the benefits of a MedD over a generally healthy diet. 

In a prospective cohort study on 140 women (mean age: 32.4 years) with primary infertility, Jahangirifar et al. (2018) studied the effect of dietary patterns on oocyte number and quality and the outcomes of ART. The researchers stated that by looking at the overall diet of infertile women rather than individual nutrients, a study such as this one could potentially be more realistic because it reflects how food is consumed and the complicated interactions between nutrients in the diet. They identified three dietary patterns: the Healthy diet, Western diet, and Unhealthy diet. The Healthy diet included high consumption of fruits, nuts, vegetables, red and white meat, dairy, green olives, cream, and legumes. The Western diet featured high consumption of sweets, caffeinated drinks, potatoes, fast foods, whole grains, refined grains, liquid oils, and salt. Finally, the Unhealthy diet was comprised of high consumption of mayonnaise, butter, eggs, junk foods, and solid oils. Greater adherence to the Healthy diet was linked to an increase in the average number of oocytes, whereas high adherence to the Unhealthy diet was linked to a significantly lower chance of getting pregnant. The researchers hypothesized that the notable increase in fruits, vegetables, and nuts in the Healthy diet could have contributed to an increase in antioxidant intake, which may have a positive effect on oocyte number and quality. The study concluded that nutrition status and dietary patterns could affect infertility treatment outcomes, and nutritional interventions prior to attempting infertility treatments could “improve outcomes, reduce costs, and increase the mental and fertility health in couples.”  

In a nested case-controlled study of 485 women (mean age: 31.3 years) and 1,669 controls (mean age: 33.1 years), Toldeo et al. (2011) searched for associations between dietary patterns and difficulty conceiving. The study participants had reported having difficulty getting pregnant, whereas the age-matched controls reported having had at least one child. Two dietary patterns were identified: ‘‘Mediterranean-type’’ and ‘‘Western-type’’ patterns. A higher adherence to the MedD was linked to a lower risk of difficulty getting pregnant compared with the lowest quartile of MedD adherence. These women were less likely to consult a physician due to difficulty getting pregnant. There was no association between the Western diet and this outcome; it had neither a protective nor harmful effect. The researchers emphasized the importance of analyzing associations between dietary patterns and health outcomes rather than separate foods or nutrients, as this approach more closely resembles the reality of the average individual. They concluded that greater adherence to a MedD pattern may enhance fertility. 

Conversely, Sugawa et al. (2018) performed a prospective study on 140 Japanese women (mean age: 37.0 years) undergoing IVF/ICSI treatment and found no association between dietary patterns and treatment outcomes. Three dietary patterns were identified: Vegetable and Seafood (i.e. vegetables, fish, seafood, soy products, and chicken), Western (i.e. red meat, chicken, and oils), and Rice and Miso Soup. Thirty-six women had clinical pregnancies during the study, but no associations were found between these women and any of the three dietary patterns. The Vegetable and Seafood diet was highly correlated with intake of folate, vitamin B6, vitamin B12, vitamin D, and omega-3 and omega-6 fatty acids, which have been found to be beneficial for IVF treatment. Regardless, there were no associations found. The researchers provided two possible reasons for these findings. The higher age of the participants could have negated the effects of a healthy diet. Also, the small sample size could have affected the results of the study, denying the ability to identify more modest effect differences. 

PCOS is one of the most frequent endocrinology disorders among women of reproductive age and the most common cause of anovulatory infertility. In a case-control study, Hosseini et al. (2017) evaluated the effect of a Healthy Eating Index (HEI) on PCOS risk. The study population was made up of 297 women, 99 of whom had PCOS (mean age: 29.0 years) and 198 were age- and BMI-matched controls (mean age: 29.5 years). The HEI compares individual diets to the Dietary Guidelines for Americans, which functions as the basis of nutritional policy in the United States. It was designed to examine the overall diet quality of various societies with different dietary patterns. The HEI used for this study included two main categories: adequacy (i.e. whole grains, fruits, greens, beans, vegetables, dairy, protein foods, seafood, plant proteins, and fatty acids) and moderation (i.e. refined grains, sodium, and empty calories). In the adequacy category, higher consumption resulted in a higher score, whereas in the moderation category, the maximum point value was attained if the recommended quantity or less was consumed. It was observed in this study that HEI scores were inversely related to PCOS risk. Patients with PCOS had dietary patterns that were marked by lower HEI scores than their matched controls. The researchers concluded that higher intakes of whole grains, plant proteins, and seafoods and lesser intakes of refined grains were associated with a reduced risk of PCOS. In addition, women with PCOS had notably reduced intakes of dairy products, and higher dairy intake was associated with a 69% lower risk of PCOS. 

Overall diet quality could affect nutrient intake, general health, and fertility. In a study of 60 fertile and 60 infertile Indian women (aged 25-32 years), Dhanashree et al. (2016) aimed to study the relationship between nutrient intake and fertility. The researchers found that infertile women had lower levels of iron, zinc, folic acid, as well as lower intakes of protein and calories. Intakes of green leafy vegetables, eggs, chicken, nuts, and dried fruit were higher among fertile women. Green leafy vegetables, in particular, were significantly correlated with fertility in these women. Leafy greens are high in folic acid, which may have a positive effect on fertility. Frequency of green leafy vegetable intake was highest in fertile women and the most fertile women (40%) consumed them three times per week. This study showed how diet quality and overall nutrient intake may affect female fertility. 

Research studies such as the Nurses’ Health Study II have hypothesized that subfertile women should increase protein and iron intake from plant rather than animal sources (Collins & Rossi, 2015). However, Jacobsen et al. (2014) found that high intake soy isoflavones may actually reduce a woman’s ability to get pregnant. This cross ­sectional study followed 11,688 North American Adventist women (mean age: 42.0 years). According to the general principals of the Adventist church, the participants were largely vegetarian (54%) and led healthy lifestyles with very low prevalence of smoking and alcohol use. Perhaps due to the large prevalence of vegetarians in this population, the mean soy isoflavone intake (17.9 mg per day) was very high compared to other Western populations; only 6% of the participants indicated no intake of soy isoflavones. Soy products are generally considered a healthy protein alternative to meat. However, women with high isoflavone intake were found to have an increased risk of never having been pregnant or given birth to a live child. The researchers found that when isoflavone intake exceeded about 40 mg per day, the overall lifetime risk of never becoming pregnant increased by 13%. However, a limitation to the study could be that the researchers were not able to distinguish between voluntary and involuntary childlessness. More research is necessary to determine the effect of soy intake on female fertility. 

Finally, Tabernero-Rico and Garcia-Velasco (2019) created an observational study on how social determinants of health (SDH) affect female fertility. The study included 200 subfertile (mean age: 32.8 years) and 197 nonsubfertile women (mean age: 30.8 years) recruited from a hospital in Madrid, Spain. SDH included biological factors such as age, ethnic origin, and BMI; behavioral factors such as alcohol intake, smoking, coffee, dietary restriction, physical activity, and psychological state; and contextual factors such as education, work activity, and income level. In terms of dietary patterns for the purpose of this project, the researchers found a positive correlation between female fertility and regular fish consumption. According to the study, the inclusion of fish once or twice a week was associated with a 60% reduction in the risk of subfertility. The researchers found no association between fruit and vegetable consumption and fertility. Also, regular physical exercise 3 or 4 days per week led to a 67% decrease in the risk of subfertility. In addition, weight control by means of restricting calorie intake, especially in the presence of obesity, was associated with improved fertility. Finally, the study showed that subfertile women were on average older the nonsubfertile women. Biologically, age is a principal factor affecting natural fertility, as reproductive capacity in women declines dramatically after age 35. The researchers concluded that weight control, fish consumption, regular physical exercise, and lower age were all positively associated with female fertility. 

Male Studies

A study from Efrat et al. (2018) compared four different dietary patterns with semen quality in an attempt to reveal real-world nutritional recommendations to improve male fertility. The study included 280 men (mean age: 33.5 years) who attended a fertility clinic between 2012 and 2015. Dietary patterns included: the HEI, DASH diet, alternate Mediterranean Diet score (aMED), and Alternative Healthy Eating Index (AHEI). The HEI guidelines include an abundant intake of vegetables, fruits, whole grains, and low-fat dairy products with lower intakes of refined grains, saturated fatty acids, and added sugars. The AHEI is similar to the HEI, but takes into account evidence-based recommendations on how certain foods and nutrients predict the risk of chronic diseases (Al-Ibrahim & Jackson, 2019). The DASH diet was defined as rich in vegetables, fruits, and whole grains; moderate in low-fat dairy products; low in sugar-sweetened beverages, sodium, and animal protein; and with high intakes of plant protein from legumes and nuts. Finally, the aMED score was based on the intake of nine food groups common to the MedD: vegetables, legumes, fruit and nuts, dairy, cereals, meat and meat products, fish, alcohol, and the ratio of monounsaturated to saturated fat. The study found that adherence to any of the four dietary indexes was associated with better sperm quality: improved total sperm count, concentration, morphology, and motility. However, the AHEI was the best associated of the four patterns. The study of whole dietary patterns shows promise for the development of realistic dietary recommendations for men suffering from infertility.

In a cross-sectional study on the MedD and semen parameters, Karayiannis et al. (2017)  followed 225 subfertile men (median age: 38 years). The participants completed a FFQ and each person was assigned a MedDietScore to rate their level of adherence. Greater adherence to the MedD was found to be significantly associated with higher sperm concentration, total sperm count, and sperm motility. Conversely, men with the lowest MedDietScores had about 2.6 times greater likelihood of having abnormal sperm concentration, count, and motility. The researchers suggested several mechanisms which may help to explain this positive association. First, the MedD is high in favorable anti-inflammatory nutrients, which could have positive effects on the reproductive system. It is also marked by high intake of omega-3 fatty acids from seafood, and the testes have high levels of active fatty acid metabolism. The MedD is also marked by low intake of saturated and trans-fatty acids, which have been shown to negatively affect semen quality. Finally, the MedD features high intake of fruits and vegetables, which are rich in antioxidants that have been suggested to improve semen quality. 

In a study comparing the Prudent diet and the Western diet, Jurewicz et al. (2018) analyzed the effects of dietary patterns on  both semen quality parameters and reproductive hormone levels. The study population consisted of 336 men (mean age: 32 years) attending an infertility clinic for diagnostic purposes. The participants had either normal semen concentration or slight oligozoospermia (semen concentration of 15-20 mln/ml). The men were grouped into one of three dietary patterns: Western (n=150), Prudent (n=90), or Mixed (n=96). The Prudent pattern was characterized by high intakes of fish, chicken, fruit, cruciferous vegetables, tomatoes, leafy green vegetables, legumes, and whole grains. The Western pattern was marked by high intakes of red and processed meat, butter, high-fat dairy, refined grains, pizza, snacks, high-energy drinks, mayonnaise, and sweets. The Mixed group was created for participants who did not fall exclusively into the Western or Prudent categories. The study found that the Prudent diet was positively associated with both sperm concentration and testosterone level, and negatively associated with DNA fragmentation index (DFI). The researchers concluded that nutrition and dietary patterns could affect semen quality and reproductive hormone levels and that men consuming the Prudent diet may have improved sperm concentration and testosterone levels with a reduced DFI. The findings also highlighted the relationship between unhealthy diets and the decline of semen quality in industrialized countries. 

Similarly, Gaskins et al. (2012) studied the effects of the Western and Prudent dietary patterns on the semen parameters of 118 healthy young men (mean age: 19.7 years). The Prudent pattern was positively associated with progressive sperm motility, yet unrelated to sperm concentration and morphology. The Western pattern was not associated with any semen parameter. The researchers concluded that a diet rich in fruits, vegetables, chicken, fish, and whole grains could function as a safe and cost-effective method to improve at least one measure of semen quality. 

Oostingh et al. (2017) studied 129 male partners (median age: 36 years) of recently pregnant women from a hospital setting. Two dietary patterns were identified: “unhealthy’’ (high intakes of dairy, mayonnaise, margarines, sauces, snacks, and sweets) and “healthy” (high intakes of cereals, fruits, legumes, vegetables, and olive oil). The study found that high adherence to the healthy dietary pattern was associated with better semen quality, especially in men with poor semen quality (i.e. total motile sperm count less than 10 million spermatozoa). Conversely, high adherence to the unhealthy pattern showed a reduction in semen quality. The intake of healthy fats (i.e. polyunsaturated fatty acids, eicosapentaenoic acid, and docosahexaenoic acid) was higher in men who adhered to the healthy diet, and the researchers believed that the positive effects of these compounds may have contributed to the increased sperm count. They also stated that the replacement of healthy fats with trans fatty acids and the high sugar intake of unhealthy dietary patterns may negatively influence semen quality. Finally, the healthy diet featured higher intakes of micronutrients, which may improve testicular development, spermatogenesis, and sperm motility. The researchers concluded that “counseling on dietary patterns, for both women and men, should be implemented in preconception care worldwide.” 

A recent cross-sectional study from Nassan et al. (2020) assessed the relationship between dietary patterns and testicular function in 2,935 young Danish men (median age: 19 years). Four diets were identified: Western, Prudent, Open-sandwich (a traditional Danish eating pattern), and Vegetarian-like. The Open-sandwich pattern featured greater intake of cold processed meats, whole grain breads, mayonnaise, cold fish, condiments, and dairy. The researchers cited a recent meta-analysis that found that sperm count had declined by 50% to 60% in Western countries between 1973 and 2011. The greatest adherence to the Prudent pattern was associated with the highest total sperm count, followed by adherence to Vegetarian-like and Open-sandwich patterns. Adherence to the Western pattern was marked by significantly lower sperm counts than in the other three patterns. In general, healthier dietary patterns could improve semen parameters and testicular function. Local variations to generally healthy diets (i.e. the Open-faced sandwich pattern for the Danish) could offer fertility benefits that better align with the traditional diets of various cultures.

In another large cross-sectional study on the effects of dietary patterns and semen quality, Liu et al. (2014) studied 7,282 healthy Taiwanese men (mean age: 31.75 years). The participants were categorized into five groups: the Healthy diet, Western diet, High-carbohydrate diet, High sweet snacks & sugar-sweetened drinks, and High-sodium diet. The researchers found no association between the Healthy diet and any semen parameters. However, the study showed a decline in semen quality for the other diets analyzed. Specifically, the Western diet resulted in a decline in sperm count and normal sperm morphology, the High-sweets diet correlated with lower sperm count, the High-carbohydrate diet related to higher prevalences of abnormal total sperm motility and progressive motility, and the High-sodium diet related to an elevated prevalence of abnormal sperm morphology. The researchers concluded from these findings that fat-rich foods such as meat and milk may decrease semen quality, as the Western diet featured higher intakes of dairy, meat, and saturated and trans fatty acids. They also cited several studies that agreed with their findings that a diet high in sweets and sugar may negatively affect sperm parameters. The researchers were surprised, however, by the negative associations found with a diet high in carbohydrates, as carbohydrates are a major staple of the typical Asian diet and a notable difference from the Western style. The researchers were also surprised that the Healthy diet, rich in fruits and vegetables, was not associated with any semen parameters. They gave one possible explanation that the presence of pesticides and pollutants could have negated the beneficial effects of the fruits and vegetables, as they have been found in other studies to associate with reduced semen quality.

Danielewicz et al. (2018) conducted another cross-sectional study with similar results. The participants included 114 Polish men (mean age: 27.2 years). Two dietary patterns were derived: Pro-Healthy and Western. Similar to the previous study, the researchers found no association between the Pro-Healthy diet and semen quality, yet did find a negative relationship with the Western diet. Stronger adherence to the Western dietary pattern was positively associated with abnormal sperm progressive motility, sperm morphology, and sperm count. The researchers determined that animal products such as red meat, processed meat, and dairy may contribute to a decline in sperm quality due to their high content of saturated and trans fatty acids. Similar to Liu et al. (2014) mentioned previously, they hypothesized that pesticide contamination could negatively affect semen quality when consuming increased amounts of fruits and vegetables. In addition, they stated that high consumption of legumes, especially soy, could reduce sperm quality. The researchers referred to studies which found that increased intake of soy isoflavones reduced sperm concentration. The study concluded that the Western dietary pattern may negatively affect sperm progressive motility, count, and morphology, and larger studies would be needed to identify associations between healthy dietary patterns and semen quality.

Lifestyle modifications may affect fertility differently when used in combination. However, multiple lifestyle factors are not often researched together to determine their synergistic affect on semen parameters. Danielewicz et al. (2019) investigated the combined effect of diet and physical activity on semen quality. This cross-sectional study followed 207 men (median age: 26 years) to examine the association between semen quality and the DASH diet, physical activity, and the two separately and in combination. The DASH diet is often linked with prevention and treatment of hypertension, diabetes, obesity, and coronary artery disease. It is marked by a healthy eating pattern of foods high in vitamins, minerals, and antioxidants, while limiting consumption of saturated fat, sugar, and sodium. The study found that physical activity and DASH diet adherence both individually correlated with improved sperm parameters. However, this association was even greater when the two were used in combination. Adherence to the DASH diet combined with physical activity was positively correlated with sperm concentration, count, motility, and morphology. Due to these findings, the researchers recommended the use of the DASH diet and physical activity together as a better method for improving semen quality.

In a study on the effects of fruit and vegetable intake (FVI) and pesticide residues on semen quality, Chiu et al. (2015) examined 155 men (median age: 36 years) in subfertile couples presenting for evaluation and treatment at a fertility center. Fruits and vegetables were categorized as containing low-to-moderate or high pesticide residues. The study found total FVI to be unrelated to semen quality parameters. However, the study also found a relationship between high pesticide residue and reduced semen quality. Specifically, high levels of pesticides reduced total sperm count, ejaculate volume, and percentage of morphologically normal sperm. Conversely, intake of low-to-moderate pesticide residue fruits and vegetables was related to a higher percentage of morphologically normal sperm. The researchers concluded that dietary exposure to pesticides may negatively impact semen quality in men.

One year later, Chiu et al. (2016) investigated the relationship between FVI, pesticide residue status, semen quality, and reproductive hormone concentration in healthy young men. In the study of 189 men (median age: 19.6 years), the researchers used a FFQ to assess dietary intake during the previous year. Semen was assessed for total sperm count, concentration, morphology, motility, ejaculate volume, total motile count, and total normal count. Total FVI was  again determined to be unrelated to semen quality, yet FVI with low-to-moderate pesticide residue was associated with higher total sperm count and concentration. FVI with high pesticide residue was unrelated to semen quality. No associations were observed between FVI and reproductive hormone concentrations, regardless of pesticide-residue status. Because FVI with low-to-moderate pesticide residue was positively correlated to sperm count in healthy young men, the researchers concluded that pesticide residues may modify the beneficial effects of FVI on semen quality.

Discussion

Of the eleven studies included on female fertility, nine studies found a positive correlation between a healthy dietary pattern and reproductive wellness. All five of the studies that focused on the MedD found positive effects on female fertility (Boghossian et al., 2013; Karayiannis et al., 2018; Sun et al., 2019; Toldeo et al., 2011; Vujkovic et al., 2010). The MedD was found to improve embryo yield, improve oocyte quality and quantity, increase the chances of pregnancy after IVF treatment, improve body fat composition, reduce the incidence of weight gain, and lower the chances of consulting a physician for infertility. A generally healthy diet was also found to increase the average number of oocytes in women undergoing ART treatment (Jahangirifar et al., 2018). This could be due to higher antioxidant intake from fruits, vegetables, nuts, and legumes. Hosseini et al. (2017) found that a healthy diet lowered the risk of PCOS, an endocrinology disorder and the most common cause of anovulatory infertility. In addition, fish intake (1-2 times per week), regular exercise (3-4 times per week), and weight control by means of caloric restriction were found to benefit female fertility (Tabernero-Rico & Garcia-Velasco, 2019). It is important to look at how dietary patterns and other determinants of health may work together to affect natural fertility. Overall nutrient intake may also be higher in fertile women (Dhanashree et al., 2016). Infertile women in this study were found to have lower levels of iron, zinc, and folic acid, as well as lower intakes of protein and calories than fertile women. Green leafy vegetables, which are high in folic acid, were particularly correlated with fertility in these women.

Only one female study found no correlation between a healthy diet and fertility (Sugawa et al., 2018). In this study, neither healthy nor unhealthy diets were associated with clinical pregnancy during IVF treatment. Another study found that high intake of soy isoflavones reflected a reduced ability to conceive (Jacobsen et al., 2014). This could warn women to be conscious of their soy intake while attempting pregnancy, especially if they are vegetarian or trying to reduce their meat consumption. 

Of the eleven studies included on male fertility, seven studies found that a healthy diet benefited male fertility. In a study comparing four different healthy eating patterns (HEI, DASH, aMED, and AHEI), Efrat et al. (2018) found that adherence to any of the four indexes could improve total sperm count, concentration, morphology, and motility. The MedD was also associated with higher sperm concentration, total sperm count, and sperm motility (Karayiannis et al., 2017). This could be due to anti-inflammatory nutrients, high intakes of omega-3 fatty acids, reduced intakes of saturated and trans-fatty acids, and/or high antioxidant intakes from fruits and vegetables. Three studies found that a Prudent diet may improve male fertility parameters (Jurewicz et al., 2018; Gaskins et al., 2012; Nassan et al., 2020). The Prudent diet was found to improve sperm concentration, testosterone levels, progressive sperm motility, and sperm count. Adherence to a healthy dietary pattern was associated with better semen parameters, especially in men with particularly poor semen quality (Oostingh et al., 2017). This may have been due to higher intakes of healthy fats and micronutrients, or reduced intakes of trans fatty acids and sugar. Finally, the DASH diet was found to positively benefit male fertility, and this benefit was improved when combined with increased physical activity levels (Danielewicz et al., 2019). This demonstrates one possible way that lifestyle changes may work together synergistically, and highlights the importance of combining healthful lifestyle changes such as diet and exercise to improve natural fertility. 

Two studies on the effect of FVI and pesticides found no association between total FVI and male fertility (Chiu et al., 2015; Chiu et al., 2016). They did, however, find that low-to-moderate pesticide intake may benefit sperm parameters, and that high pesticide intake may negatively affect male fertility. Pesticide exposure has been thought to possibly affect semen quality and negate some of the benefits of increased FVI on male fertility. For instance, two studies that found no association between a healthy diet and male fertility speculated that this could have been caused by pesticide exposure in a diet high in fruits and vegetables (Liu et al., 2014; Danielewicz et al., 2018). These two studies found no associations for a healthy diet on semen parameters, yet found negative associations with unhealthy diets. This leads to the conclusion that a diet high in fruits and vegetables should not negatively affect male fertility, regardless of pesticide contamination; however, an unhealthy diet may decrease semen parameters.

Overall, 77.3% (17 out of 22) of the studies analyzed in this review found a positive correlation between healthy dietary patterns and reproductive wellness for women and men. Because it is possible that pesticide intake could affect the positive benefits of a healthy diet high in fruits and vegetables, organic produce should be consumed whenever possible to improve fertility parameters. Also, dietary patterns such as the MedD and the Prudent diet do not appear to worsen fertility status, although studies have found that unhealthy diets may negatively affect fertility. Healthful diets should be recommended for all couples to improve both the chance of pregnancy and the health of the mother upon conception. Preconception lifestyle and nutrition counseling is a beneficial idea for any couple attempting to conceive.

Nutritional Guidelines to Enhance Fertility

Based on the analysis of the dietary patterns above, there are several nutritional guidelines that can be used to help enhance fertility in both women and men. 

Abundant Intake

Fruits and vegetables. Fruits and vegetables are high in antioxidants, which may improve fertility. Unlike supplements, the diet contains antioxidants in ideal proportions and combinations to suppress the formation of reactive oxygen species (Karayiannis et al., 2018). High FVI has also been found to improve embryo quality in women and fertilization rates in men. Also, leafy green vegetables are particularly high in folic acid, which has been shown to benefit fertility (Dhanashree et al., 2016). However, organic produce should be consumed whenever possible to limit exposure to pesticides and chemical contaminants.

Legumes, whole grains, and nuts. Legumes, whole grains, and nuts should also be consumed in abundance. The MedD, for instance, has been associated with maintaining a favorable body weight, possibly due to a higher consumption of satiating dietary fiber (Boghossian et al., 2013). Also, the low energy density and low glycemic load of the MedD may lead to lower caloric intake and improved metabolic control (Carlos et al., 2018). 

High-to-moderate intake

Vegetable oils. One of the markers of the MedD is a particularly high intake of vegetable oils, especially olive oil. One study found this to be one of the significant differences between the MedD and an overall healthy diet. Vegetable oils are rich in linoleic acids, omega-6 fatty acids that are precursors to prostaglandins. Prostaglandins are important for ovulation and maintenance of pregnancy, and a high intake of linoleic acid may positively affect implantation (Vujkovic et al., 2010). Also, because olive oil consumption is particularly high in the MedD, the diet features a higher ratio of monounsaturated to saturated fatty acids, which may be beneficial for fertility. 

Fish. Regular fish consumption (1-2 times per week) may benefit both female and male fertility due to omega-3 fatty acid content (Tabernero-Rico and Garcia-Velasco, 2019; Karayiannis et al., 2017). The testes have high levels of active fatty acid metabolism and omega-3s may be particularly beneficial for male fertility. However, one should also take into account the degree of contamination that could potentially outweigh the health benefits of consuming fish. Environmental pollution and mercury in fish may harm fertility and should generally be avoided (Gaskins & Chavarro, 2018). 

Low-to-moderate intake

Eggs, dairy products, and poultry. It is a useful recommendation to limit saturated fat intake and protein from animal products. In doing so, plant protein may be increased, which will also increase fiber, antioxidant, and nonheme iron intake. However, when substituting plant protein for animal protein, caution should be taken to avoid an abundance of soy in the diet. It is possible that high intakes of soy isoflavones may negatively affect female fertility (Jacobsen et al., 2014). In addition, foods such as animal fat, meat, eggs, cheese, and milk have a tendency to accumulate pesticides, which could negatively affect fertility (Pizzorno & Murray, 2013). Reducing consumption of animal protein will inherently reduce the consumption of pesticides.

Low intake

Red meat. Red meat intake is generally very low on the MedD or Prudent diet. Reducing red meat intake contributes to a reduced intake of saturated and trans fatty acids, which have been shown to negatively affect semen quality (Karayiannis et al., 2017).

Sugar and sweetened beverages. A diet high in processed sweets and sugar has been found to negatively affect sperm parameters (Liu et al., 2014). 

Avoid

Trans fats. The typical Western diet is relatively high in trans fatty acids from greater intakes of fried foods and processed snacks (Liu et al., 2014). Trans fatty acids can decrease fertility in men and women and should be replaced with monounsaturated fats. Trans fatty acids may also promote greater insulin resistance (Gaskins & Chavarro, 2018). This could negatively affect ovulatory function in women. Finally, consumption of trans fatty acids has been found to decrease total sperm count (Chavarro et al., 2014). 

Other lifestyle modifications

Physical exercise. Moderate and regular exercise has been found to benefit both male and female fertility. However, excessive exercise can negatively alter energy balance and affect the reproductive system (Sharma et al., 2013). One must ensure that energy demand is not exceeding dietary energy intake. Extreme exercise can also lead to anovulation, the absence of ovulation, whereas moderate exercise may decrease the risk of infertility in women (Collins & Rossi, 2015). The exact amount of exercise that will improve the fertility of each individual must be assessed on a case-by-case basis.

Body weight. Being underweight or overweight can negatively affect fertility. A healthy BMI is considered to range between 18.5 and 24.9, whereas a person is considered overweight with a BMI over 25, and obese if the BMI is over 30. Obesity has been found to negatively impact semen concentration and quality in men, and time to pregnancy and risk of miscarriage in women (Sharma et al., 2013). Being underweight can also negatively affect the fertility of both women and men. 

Stress reduction. Psychological factors are also important to consider. Stress can alter levels of follicle stimulating hormone and luteinizing hormone, which directly affect the synthesis of estrogen and progesterone and control ovulation in women (Chasse, 2013). These hormones also dictate spermatogenesis and testosterone production in men. Increased levels of stress have been found to negatively impact sperm parameters, and depression may lower testosterone levels (Sharma et al., 2013). Infertility diagnosis and treatments can cause a great deal of stress for couples, creating a negative cycle that makes it even more difficult to conceive. Examples of stress reduction techniques include: meditation, yoga, acupuncture, exercise, journaling, creative artistic expression, and time spent outside in nature. 

Multi-micronutrient supplements. Inadequate levels of micronutrients can affect fertility. It is well documented that folic acid supplementation prevents neural tube defects during pregnancy, however studies have also found that multi-micronutrient supplementation may have a positive impact on fertility (Schaefer & Nock, 2019). Multi-micronutrient supplementation may enhance reproductive health by helping to restore nutrients to recommended levels and by strengthening the antioxidant defense system. This may improve oocyte and embryo quality, reduce the time to conception, and increase a woman’s chances of becoming pregnant. 

Caffeine intake. There are varying results as to whether or not caffeine intake affects fertility. Some studies have found that caffeine intake increases the time to pregnancy in women, concluding that it should be consumed in moderation (Sharma et al., 2013). Other studies have found that caffeine intake has no significant effect on time to pregnancy or ovulatory disorder infertility (Collins & Rossi, 2015). More research is needed to determine the exact relationship between caffeine intake and fertility. Coffee has been found to increase the risk of spontaneous abortion, although it is still unclear whether it affects fecundity (Lyngsø et al., 2017). Reduction of caffeine intake does not appear to worsen fertility, and it may possibly help.

Alcohol intake. The impact of alcohol on fertility is not entirely clear. However, some studies have found alcohol consumption to reduce sperm quality and increase the risk of infertility in women (Sharma et al., 2013). The MedD, which was found to have a positive impact on fertility in each study analyzed here, is generally considered to include a regular but moderate intake of alcohol, mainly wine during meals (Boghossian et al., 2013). It is advisable to reduce alcohol intake while trying to conceive and immediately cease all alcohol intake while pregnant. 

Cessation of smoking. Smoking is one of the most readily avoidable causes of infertility (Pizzorno & Murray, 2013). In women, smoking has been found to increase the thickness of the zona pellucida, the membrane that forms around an ovum, making it difficult for sperm to penetrate it. In men, cigarette smoke has been associated with decreased sperm count and motility, as well as a higher frequency of abnormal sperm. 

Benefits of Preconception Counseling

Adherence to a preconception lifestyle intervention program has been found to improve diet and increase physical activity level in women with obesity and infertility (van Elten et al., 2018). In another study, a preconception lifestyle program led to reduced caloric intake 5.5 years later, and the participants who lost weight during the intervention had a lower BMI at follow-up (van Elten et al., 2019). Preconception counseling can therefore both improve the health of hopeful parents in both the short and long term. This has the potential to both increase a couple’s chances of conceiving and improve the mother’s health for pregnancy and lactation. 

Conclusion and Recommendations

When it comes to diet and pregnancy, the focus is often placed on what to eat (and what to avoid) while pregnant. With infertility rates on the rise and healthy eating patterns declining worldwide, preconception nutrition may be beneficial for the many couples struggling to conceive. Of the 22 research studies analyzed in this paper, about 77% found a positive correlation between healthy dietary patterns and fertility in women and men. None of the studies found that healthy dietary patterns actually worsened fertility status. There is nothing to lose by promoting healthy diets to subfertile men and women, and possibly quite a lot to gain.  

The MedD has consistently been associated with reduced risk of cardiovascular disease, neurodegenerative disease, cancer, and diabetes. In addition, all six of the studies analyzed in this paper that focused on the MedD found it to benefit fertility. In women, the MedD has improved embryo yield, oocyte quality and quantity, body fat composition, and the chance of pregnancy after IVF treatment. Adherence to the MedD has also reduced the incidence of weight gain in women and lowered the chance of consulting a physician for difficulty getting pregnant. In men, the MedD has improved sperm count, concentration, and motility. This dietary pattern should be promoted as a possible preconception diet for both women and men. 

The Prudent diet was found in this paper to improve sperm concentration, testosterone levels, progressive sperm motility, and total sperm count. In terms of overall health in men, it has also been linked to a reduced risk of cardiovascular disease and colorectal cancer. Similarly, a healthy dietary pattern in women has been associated with an increase in the average number of oocytes and a reduced risk of PCOS. The higher antioxidant intake of women with healthy dietary patterns may improve both oocyte quantity and quality. 

There are many similarities between these dietary patterns. For instance, both the MedD and the Prudent diet feature an abundant intake of fruits, vegetables, and whole grains. These foods are high in antioxidants which can improve health in many ways. Based on the analysis of these dietary patterns, there are several nutritional guidelines outlined above that can be promoted to help enhance fertility in both women and men. Generally, a person should increase intakes of fruits, vegetables, whole grains, nuts, legumes, fish, and vegetable oils, while decreasing intakes of refined grains, sugar, and saturated and trans fatty acids. 

A holistic approach to preconception lifestyle counseling should also include regular exercise, weight management, multi-micronutrient supplementation, cessation of smoking, reduced intake of coffee and alcohol, and stress management techniques. When taken together, an individual’s fertility is likely to improve by such a holistic approach to health. Preconception counseling provides a unique opportunity to increase a couple’s chances of conceiving naturally, improve a mother’s health for pregnancy and lactation, reduce the risk of pregnancy complications, and subsequently enhance the longterm wellbeing of a family. 

Although research studies on dietary patterns and fertility are growing in number, there is still room for improvement. The majority of studies still focus on how individual nutrients or antioxidants impact fertility, rather than considering how foods may affect health when taken together in a diet. People do not consume individual nutrients and the synergistic effect of foods taken together could impact a person’s health in a number of ways. The study of dietary patterns offers a more realistic approach for the average person who struggles with fertility. Future studies should consider using 24-hour diet recalls with frequent dietary assessments to reduce the risk of misreported consumption. Also, using age and weight matched controls will help to ensure more accurate results. 

The MedD is a useful dietary pattern to study because it is relatively well known and consistently defined. There will be subtle variances in what researchers believe constitutes the MedD, but overall, its components should not vary greatly between studies. It is a diet that has been examined extensively and is well documented in many different realms of health. However, it is also important to take into account cultural differences in diet and how a well balanced and generally healthy dietary pattern may affect fertility. Results can vary greatly between countries and ethnic populations; it is therefore crucial to perform these studies in a variety of cultures. The dietary habits of Asian populations, for instance, will differ from those of European countries. Findings from one study group may not always translate to other cultures. However, the influence of the Western diet is expanding globally and must be confronted swiftly to prevent the risk of chronic disease worldwide.

Future studies could also analyze the combined effects of diet with other lifestyle interventions on fertility status in women and men. Only one study analyzed here met these qualifications. The benefit of diet on male fertility parameters was found to be even more significant when combined with regular physical activity. Stress may also be an important contributing factor to infertility. Future studies would benefit from researching the combined effect of healthy dietary patterns with stress management techniques to potentially improve fertility. 

A person’s fertility may be considered an indicator of their overall health and wellbeing. The promotion of fertility counseling and preconception nutrition is crucial for health practitioners worldwide. Dietary intervention before conception has the potential to increase the chances of natural pregnancy, lessen the financial burdens of ART, reduce the mental stress associated with infertility, and promote the holistic health of families for years to come.

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