The Connection Between Weight (BMI) and Fertility Rate
The U.S. and global fertility rate is declining, with more couples unable to conceive and seeking reproductive care. Currently, almost 13% of couples face fertility challenges after trying to conceive for one year without success.
Many reasons help explain increasing fertility challenges, including poor nutrition, toxin exposures, factors affecting hormone balance, stress, and more. Today, we will explore the connection between weight and fertility. Does weight affect fertility? Does obesity affect fertility?
Keep reading as we dive into:
- Does being overweight affect fertility?
- Does being underweight affect fertility?
- How to increase fertility with nutrition
Before we get into the research, let’s take a moment to acknowledge the limitations of body mass index (BMI). BMI is a height and weight ratio used to classify someone as underweight, normal weight, overweight, or obese. The BMI fails to account for body composition, so that some people will be outside of a normal BMI but still healthy in terms of body composition and metabolic health. Still, this is the tool most used in the research to study the weight-fertility connection, which is why we discuss it here.
Does Being Overweight Affect Fertility?
Around 40% of women of reproductive age fall into an overweight or obese BMI category, which has implications for reproductive health and pregnancy BMI. An elevated BMI is associated with:
- Irregular menstrual cycles
- Anovulation (not ovulating)
- Decreased success with fertility treatments
- Higher rates of pregnancy complications
- Early miscarriage
On the other hand, women who intentionally experience weight loss for fertility are more likely to become pregnant.
It’s also important to note that there is a connection between obesity and fertility for male partners, too. Obesity in men is associated with decreased sperm counts and fertility. The health of sperm goes beyond conception; it’s integral for the health of the pregnancy and the health of the infant as they grow into adulthood.
Overweight and Effects on Ovulation
Excess weight (body fat) increases inflammation and oxidative stress in the body, which affects egg quality and may initiate ovarian aging. In other words, it affects ovulation and the fertility cycle, which can make getting pregnant more challenging.
Ovulation and healthy eggs are essential for healthy conception and pregnancy!
Does Being Underweight Affect Fertility?
While much of the research focuses on a high BMI, there is also a connection between low BMI and fertility. On a basic level, a chronic energy (calorie) deficiency affects the communication between the brain and the ovaries. The body interprets low calories as stress, which influences fertility hormones and can cause the loss of the menstrual cycle and ovulation.
Hypothalamic amenorrhea (HA) is the medical term when the ovulation ceases, and women lose their menstrual cycle and periods. HA is most often caused by undereating, including eating disorders. Other causes are over-exercise or rapid weight loss from starvation, infections, and chronic diseases.
Underweight and Effects on Ovulation
Being underweight (defined as a BMI below 18.5) can stop ovulation. Think of body fat as nutritional resources for fertility and pregnancy. Without enough, the body will prioritize its safety and survival above reproduction. It simply doesn’t have the resources to support a healthy pregnancy.
If you are underweight or low-normal weight and struggling with fertility issues, increasing body weight can help restore menstrual cycle regularity and fertility.
How a Healthy BMI Improves Hormones and Ovulation
Finding a healthy weight for you is less about BMI or the number on the scale. It’s more about your body composition, metabolic health, and overall health status. In addition to BMI, your medical history, menstrual cycle data, and lab work can tell us a lot about fertility and how to improve conditions to optimize conception and prepare for a healthy pregnancy.
Preconception (before you conceive) is the time to focus on nutrition and health concerns. Your health status not only affects you but also fertility, pregnancy, and the health of your future children. This goes for Dad, too. He’s not off the hook and can benefit from improving health prior to conception.
How to Improve Fertility with Diet and Nutrition
A diet to enhance fertility is about so much more than manipulating weight; it’s about nourishing the body and building the nutritional capacity to grow a baby. When you focus on giving your body what it needs, weight will often naturally regulate without forcing it in unhealthy ways.
At Lizzy Swick Nutrition we offer a personalized fertility diet to each client through our Let’s Get Pregnant! Fertility Journey.
In our self-directed or dietitian-led program, you learn the importance of:
- Diet quality
- Hydration
- Healthy fats
- Protein
- Plant-rich plates
- Balanced blood sugar
- Supporting brain-ovary communication
- Healthy menstrual cycles
- Essential fertility and pregnancy nutrients
- Adjusting meal composition
- Prenatal and fertility supplements
- Lifestyle pieces including sleep, movement, stress reduction, and a healthy mindset
- Personalization – there is no one-size-fits-all approach
- Support from a team of women who’ve been through it all!
Our comprehensive approach prepares your body for pregnancy by supporting fertility from the inside out. While weight and BMI are important, they are not the only piece of the fertility puzzle. We aim to look at the whole picture without judgment or shame, with only compassion and a deep desire to help you become and thrive as a mom.
If your doctor has told you to lose weight (or gain weight) without a deeper conversation, it’s time to add Lizzy Swick Nutrition to your fertility care team!
References
- Carson, S. A., & Kallen, A. N. (2021). Diagnosis and Management of Infertility: A Review. JAMA, 326(1), 65–76. https://doi.org/10.1001/jama.2021.4788
- McLean, S., & Boots, C. E. (2023). Obesity and Miscarriage. Seminars in reproductive medicine, 41(3-04), 80–86.
- Hunter, E., Avenell, A., Maheshwari, A., Stadler, G., & Best, D. (2021). The effectiveness of weight-loss lifestyle interventions for improving fertility in women and men with overweight or obesity and infertility: A systematic review update of evidence from randomized controlled trials. Obesity reviews : an official journal of the International Association for the Study of Obesity, 22(12), e13325.
- Ameratunga, D., Gebeh, A., & Amoako, A. (2023). Obesity and male infertility. Best practice & research. Clinical obstetrics & gynaecology, 90, 102393.
- Wang, L., Tang, J., Wang, L., Tan, F., Song, H., Zhou, J., & Li, F. (2021). Oxidative stress in oocyte aging and female reproduction.Journal of cellular physiology, 236(12), 7966–7983.
- Snider, A. P., & Wood, J. R. (2019). Obesity induces ovarian inflammation and reduces oocyte quality. Reproduction (Cambridge, England), 158(3), R79–R90.
- Boutari, C., Pappas, P. D., Mintziori, G., Nigdelis, M. P., Athanasiadis, L., Goulis, D. G., & Mantzoros, C. S. (2020). The effect of underweight on female and male reproduction. Metabolism: clinical and experimental, 107, 154229.
