Whether a certain diet could enhance pregnancy outcomes is under investigation

Infertility, defined as the inability to conceive after a year of unprotected, frequent sexual intercourse, affects an estimated 15% of all couples during their reproductive years.¹ The probability of pregnancy drops in women who are on the extremes of body mass, either underweight or obese, defined as body mass index (BMI) of 30 k/m² or higher.^2,3

The good news is that losing weight improves fertility in morbidly obese women.⁴ In particular, weight loss appears to significantly improve menstrual regularity and ovulation.⁵ However, the specific diet and micronutrients that would contribute to better pregnancy outcomes is only recently being rigorously investigated. This is especially timely, because nearly half of reproductive-aged women in the United States are overweight or obese.⁶ Our goal here is to concentrate on studies addressing diet as it relates to fertility.

Excess weight and anovulation

It has long been known that the pathogenesis of PCOS involves insulin resistance and exaggerated ovarian androgen production, but the precise relationship of these processes is still incompletely understood. Although obesity is a frequent feature of PCOS, it is not a part of the accepted diagnostic criteria.⁹ Moreover, non-PCOS obesity is a well-recognized cause of reproductive impairment on its own, with study after study describing a detrimental influence on reproduction even when a woman has a normal menstrual cycle. Obesity prolongs the time to pregnancy and decreases the likelihood of pregnancy in women with regular menstrual cycles.¹⁰ Obesity as a potential cause of infertility was described as long ago as 1328 in a Bible commentary by a medieval scholar.¹¹ Yet the understanding of the mechanisms underlying this association is still in its infancy.

Altering food intake to affect fertility is also not new. In the early 20th century, married women in Cheshire, England, were reportedly known to eat a local "fertility loaf" of whole wheat and wheat germ credited with promoting fertility in farm animals.¹² In some cultures, ethnobiologists have noted links between eating fish eggs and "fertility and effective childbearing."¹³ From the "fertility breads" in agricultural societies to a root vegetable known as maca in Peruvian communities, many cultures still retain seemingly peculiar food traditions to encourage successful conception.¹⁴ Although intriguing, none of these studies rigorously examine populations large enough to confirm or refute the effects of dietary alterations to promote fertility.

Weight loss and exercise

Weight loss to improve fertility, mainly through diet and lifestyle changes, has been studied in patients with anovulatory disorders.

In a small study, researchers reported that over a 6-month period, weight loss averaging 6.3 kg with exercise and lifestyle management led to 12 out of 13 women studied resuming ovulation.⁴ Bear in mind, however, that these results were accomplished in an aggressive intervention program and don't always apply to general clinical practice.

Weight loss brought about by bariatric surgery in morbidly obese women has been reported to improve a variety of reproductive markers such as ovulation and pregnancy rates.¹⁵ A major drawback of most currently available bariatric surgery studies that report improved fertility is their small sample size and the lack of an appropriate control group of medically managed patients.

However, even as larger bariatric surgery data become available, we need more information to understand how less extreme interventions, such as modifying one's diet, fit in with efforts to improve fertility.