Fertility: The Impact of Bacteria and Food Choices

Savannah Helm

By: Alicia Jerome MS, RDN

In 2021, there were over 3.6 million babies born in the United States.1 The mean age of a woman’s first birth in 2021 was 27 years. That is 6 years later than the mean age of a woman’s first birth in 1970.2 Clare Fleishman MS, RDN, author of Fertility: Why Microbes, Weight & Nutrition Matter, suggests that this delay can be attributed to the increased desire for women to pursue education and a career but, it may be also affected by concerns for the state of our current world: political unrest, pandemic, etc.3 Fleishman also suggests that student debt, unaffordable childcare, and rising prices as additional deterrents to parenthood.

This delay in motherhood also presents its own challenges to a woman’s fertility. A woman’s prime fertile years are in her 20’s. Upon reaching 30 years old, fertility steadily begins to decline, especially after 35. Consider that 20 of 100 women in their 30’s will get pregnant in 1 menstrual cycle while only 5 out of 100 will be successful when they reach 40.3 Not only is biology at play but one cannot rule out stress, environmental factors, and food choices.

One interesting area of research on fertility is the microbiome. The Human Microbiome Project reported that vaginal microbiota makes up nearly 10% of the total body microbiota.4 Even more fascinating is that in the last few years, research has shown that the upper female reproductive system (ovaries, Fallopian tubes, and uterus), which was once considered sterile, has microorganisms.5

The most abundant genus bacteria in the female reproductive tract are lactobacillus.3 They serve as a physical barrier to pathogens by adhering to the epithelial cells of the vagina. Fleishman states, “These resident microbes markedly contribute to health. Alterations have been linked to several gynecological diseases, including chronic endometriosis, endometriosis, pelvic inflammatory disease, and gynecological cancers.”3 For men, the presence of these same bacteria, lactobacillus, were the determinant for classifying good-quality semen.8

Keeping the helpful and harmful bacteria balanced in both the male and female reproductive systems may be an effective way to treat fertility. Consider that 20% of women with infertility have bacterial vaginosis.7 When men had microbiome dysbiosis, they too, had higher incidences of infertility. When both men and women were treated with supplemental probiotics, fertility improved.3

Another factor in fertility, for both men and women, is weight. Compared to non-obese women, the risk of infertility in obese women is three times higher and increases time to conceive.8 Even without weight loss, obese women had great fertility treatment success when they incorporated physical activity3. However, as great as exercise is, the treatment that produced the highest pregnancy rates in obese women was bariatric surgery.3

For a dietitian, educating would-be mothers and fathers on foods that can improve fertility may be another effective treatment. There is increasing evidence for choosing unsaturated fats, plant-based proteins, and low-glycemic carbohydrates for the fertility of both men and women. These principles line up succinctly with the Mediterranean Diet, which provides a multitude of benefits outside of fertility.

The use of vitamins and minerals for improving fertility has largely been unexplored. While some nutrients have limited evidence, there is increasing proof for a variety of micronutrients, as well as antioxidants, amino acids, and phytochemicals. Two that are uniquely interesting are resveratrol and melatonin.

While infertility can be an emotional, physical, and mental burden, there is comfort in knowing that we live in a day of modern medicine and research and that each new day brings us closer to more solutions and more hope.

If you want to find out more about the impact of food, microbes, and weight on fertility (for both women and men) consider reading, Fertility: Why Microbes, Weight & Nutrition Matter and taking its exam for 15 CPE hours credit.



  1. Centers for Disease Control and Prevention. (2023, February 23). FastStats - Births and Natality. Centers for Disease Control and Prevention. https://www.cdc.gov/nchs/fastats/births.htm
  2. Mean age of mother, 1970–2000 - Centers for Disease Control and ... (n.d.). https://www.cdc.gov/nchs/data/nvsr/nvsr51/nvsr51_01.pdf
  3. Fleishman, C. Fertility: Why Microbes, Weight & Nutrition Matter. 2022. Origin Story Press.
  4. Turnbaugh, P., et al. “The human microbiome project.” Nature 449,7164 (2007): 804-810. Doi:10.1038/nature06244
  5. Moreno, I., Carlos S. “Deciphering the effect of reproductive tract microbiota on human reproduction.” Reproductive medicine and biology, 18,1 40-50. 1 Nov 2018, doi: 10.1002/rmb2.12249
  6. Tomaiuolo, R., et al. “Microbiota and Human Reproduction: The Case of Male Infertility.” High-throughput, vol 9,2 10. 13 April 2020, doi:10.3390/ht9020010
  7. van Oostrum, N., et al. “Risks associated with bacterial vaginosis in infertility patients: a systematic review and meta-analysis.” Human reproduction (Oxford, England), vol. 28,7 (2013): 1809-15. doi:10.1093/humrep/det096
  8. Silvestris, E., et al. “Obesity as disruptor of the female fertility.” Reproductive biology and endocrinology: RB&E, 16,1 22. 9 Mar. 2018. Doi:10.1186/s12958-018-0336-z

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