Expert Review
Diet and fertility: a review

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The literature on the relationship between diet and human fertility has greatly expanded over the last decade, resulting in the identification of a few clear patterns. Intake of supplemental folic acid, particularly at doses higher than those recommended for the prevention of neural tube defects, has been consistently related to lower frequency of infertility, lower risk of pregnancy loss, and greater success in infertility treatment. On the other hand and despite promising evidence from animal models, vitamin D does not appear to exert an important role in human fertility in the absence of deficiency. Antioxidant supplementation does not appear to offer any benefits to women undergoing infertility treatment, but it appears to be beneficial when it is the male partner who is supplemented. However, the available evidence does not allow discerning which specific antioxidants, or at which doses, are responsible for this benefit. Long-chain omega-3 fatty acids appear to improve female fertility, although it remains unclear to what extent contamination of shared food sources, such as fish with high levels of environmental toxicants, can dampen this benefit. Lastly, adherence to healthy diets favoring seafood, poultry, whole grains, fruits, and vegetables are related to better fertility in women and better semen quality in men. The cumulative evidence has also piled against popular hypotheses. Dairy and soy, once proposed as reproductive toxicants, have not been consistently related to poor fertility. In fact, soy and soy supplements appear to exert a beneficial effect among women undergoing infertility treatment. Similarly, because data from large, high-quality studies continue to accumulate, the evidence of a potentially deleterious effect of moderate alcohol and caffeine intake on the ability to become pregnant seems less solid than it once did. While a complete picture of the role of nutrition on fertility is far from complete, much progress has been made. The most salient gaps in the current evidence include jointly considering female and male diets and testing the most consistent findings in randomized trials.

Section snippets

Antioxidants

A 2013 Cochrane review of randomized controlled trials (RCTs) of antioxidant supplementation during the course of infertility treatment concluded that the current evidence does not show benefits of female antioxidant supplementation for increasing pregnancy or live birth rates.10 The authors pointed out many deficiencies of the available evidence including a high risk of bias, incomplete reporting, and high variability of the interventions tested in the trials.10 For example, the trials

Fatty acids

In vitro studies have shown that fatty acids are important substrates in early reproductive events including oocyte maturation71 and embryo implantation.72 Moreover, animal and human studies suggest that polyunsaturated fatty acids (PUFAs) may have a specific impact on fertility, through effects on oocyte quality and embryo implantation73, 74 while trans fatty acids may promote greater insulin resistance,75 which could adversely affect ovulatory function.76

Results from the NHS-II cohort

Dairy

Dairy foods have been suggested as potential reproductive toxicants because of their high content of galactose, which in mice was shown to decrease ovulation and lead to premature ovarian failure,83, 84 and their potential to contain high amounts of environmental estrogens.85 In 1994 an ecological study among 31 countries was published showing that the decline in fertility with age is steeper among populations with higher per-capita milk consumption.86 However, a subsequent case-control study

Meats, fish, and soy

Intake of protein sources has received attention in the context of fertility, mostly because of their potential to contain high levels of environmental contaminants, which could adversely affect reproductive health. While red meats can be good sources of protein and other essential nutrients, they also contain high levels of saturated fat and can serve as a vehicles for exposure to hormonal residues, antibiotics, and polybrominated diphenyl ethers.91, 92

Similarly, while seafood is a recognized

Dietary patterns

To date, 2 studies have examined the relationship between preconception dietary patterns and risk of infertility.111, 112 In the NHS-II, women in the highest quintile of an investigator-generated fertility diet score, which prioritizes higher intakes of protein from vegetable sources, full-fat dairy foods, iron, the ratio of monounsaturated fatty acids to trans fats, and more frequent use of multivitamins and lower intakes of protein from animal sources, dietary glycemic load, and low-fat dairy

Alcohol and caffeine

Intakes of caffeine and alcohol are, unquestionably, the most studied dietary factors as potential disruptors of fertility, with more than 30 studies on this topic to date. Results, however, are inconsistent, with multiple studies showing deleterious effects of caffeine116, 117, 118, 119, 120, 121, 122, 123, 124, 125 and alcohol,126, 127, 128, 129, 130, 131 but just as many studies showing no association125, 126, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144 or even improved

Paternal diet

The role of paternal diet on semen quality and couple fertility has been recently examined and summarized in several systematic reviews.153, 154, 155, 156 Some general trends are worth brief mention. First, a Cochrane review of randomized trials of antioxidant supplementation for men in couples undergoing infertility treatment found evidence of benefit for antioxidant supplements in improving semen quality and clinical pregnancy rates.153 Despite the evidence for benefit, the large

Conclusion

The literature on the relationship between diet and human fertility has greatly expanded over the last decade and led to the emergence of some clear patterns. Intake of supplemental folic acid has been consistently related to numerous markers of female fertility, from lower frequency of anovulation to higher reproductive success in the setting of ART, suggesting that the reproductive benefits of folate extend beyond the prevention of NTDs.

On the other hand, despite promising evidence from

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  • Cited by (0)

    This study was supported by grant K99ES026648 from the National Institutes of Health, grant R01ES009718 from the National Institute of Environmental Health Sciences, grant L50-HD085359 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and grant P30DK46200 from the National Institute of Diabetes and Digestive and Kidney Diseases.

    The authors report no conflicts of interest.

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