A new study published in the journal Reproductive Toxicology reviews current evidence supporting the role of nutrition as a modifiable risk factor for female infertility and poor in vitro fertilization (IVF) outcomes.

Study: Nutrition, female fertility and in vitro fertilization outcomes. Image Credit: Prostock-studio / Shutterstock.com

Introduction

Infertility is defined as the inability to conceive and become clinically pregnant after 12 months of unprotected intercourse. Current estimates indicate that 15-20% of couples experience infertility globally.

Rising infertility rates have led researchers to become increasingly interested in identifying modifiable lifestyle and environmental factors that may affect reproductive health. The potential impact of certain dietary patterns, such as Mediterranean and Western diets, and specific foods on infertility have also been widely studied.

In the current study, researchers review the complex relationship between nutrition and fertility, with a particular focus on carbohydrates, proteins, and fatty acids.

Carbohydrates

Carbohydrates, which are the primary energy source in humans, regulate the glucose metabolic pathway and insulin-mediated glucose control. Carbohydrates range from monosaccharides or simple sugars to complex molecules like plant cell wall polysaccharides and certain oligosaccharides. The glycemic index (GI) and glycemic load (GL) are values that reflect how carbohydrates affect blood sugar levels.

GL can be reduced by consuming more complex indigestible carbohydrates, such as those found in soluble dietary fiber or whole grain food products. A higher whole-grain intake has been associated with higher pregnancy and live birth rates. Likewise, eating more vegetables has been shown to improve embryo quality following intracytoplasmic sperm injection (ICSI).

Carbohydrate intake and its breakdown also appear to regulate ovarian function. In fact, the risk of ovulatory infertility was about 80% higher among women who consumed more carbohydrates as compared to those with the lowest quintile of carbohydrate intake in the Nurses’ Health Study II (NHS II) of 2009.

A diet that with less than 45% of the total energy intake from carbohydrates has been shown to improve polycystic ovarian syndrome (PCOS) symptoms by increasing the levels of follicle-stimulating hormone (FSH) and sex hormone binding globulin (SHBG), all the while decreasing testosterone and insulin levels. This is correlated with reduced weight in overweight or obese PCOS patients.

With a hypocaloric diet, in which half of the daily calories are from carbohydrates, a greater number of ova were retrieved, and higher clinical pregnancy and live birth rates were recorded in infertile and obese infertile women during IVF. However, the consumption of sugary soda was also weakly linked to a lower number of ova retrieved and embryos obtained by ovarian stimulation cycles, in addition to a reduced live birth rate.

Proteins

A healthy adult is expected to consume 0.8 g/kg protein for each kilogram (kg) of body mass. Animal protein intake has been positively linked to ovulatory disorders compared to plant proteins. In fact, 5% of energy intake provided by vegetable proteins rather than animal proteins has been shown to reduce the risk of ovulatory disorders by more than 50%.

Dairy and soy consumption has been correlated with better outcomes during IVF. This is because soy contains phytoestrogens, a class of isoflavones with a structure resembling that of estrogen that exhibit weak estrogenic activity through estrogen receptor binding.

There is fair evidence that animal-based proteins affect female fertility as opposed to those plant-based, suggesting that proteins source may represent an important determinant of reproductive success.”

Fats

Omega-3 polyunsaturated fatty acid (ω-3 PUFAs) and omega-6 (ω-6) PUFAs are found in different types of food products. To this end, ω-3 PUFAs are often found in fish like salmon, mackerel, sardines, and tuna, as well as nuts, seeds, and plant oils. Comparatively, ω-6 PUFAs, which can also be found in nuts, seeds, and oils, are often present in poultry meat, fish, and eggs.

No definitive evidence has determined the impact of these fats on IVF outcomes; however, better pregnancy odds appear to be correlated with increased ω-3 PUFA consumption.

Nevertheless, certain foods like fish may increase the level of exposure to persistent organic contaminants like methylmercury and dioxins. Similarly, vegetable and fruit ingestion may increase the risk of pesticide exposure. 

The risk associated to the presence of these toxicologically active compounds might depend on several factors, as well as the amount of food consumed, the patients’ ethnicity and hormonal status.”

Implications

Evidences on the role of nutrition in fertility/infertility are rapidly evolving, but at this time, the available data are insufficient to fully support practicing clinicians in giving nutritional suggestion to infertile couples.”

More research is needed to examine how nutrition is related to increased exposure to endocrine-disrupting chemicals and at what levels to better understand its impact on reproductive function.