How weight contributes to infertility at a glance
- Being obese or overweight impacts fertility in both men and women, while being underweight primarily affects fertility of women.
- According to the American Society for Reproductive Medicine (ASRM), 12% of all primary infertility cases are due to the woman either being obese (6%) or being underweight (6%).
- In women, being overweight or being underweight can negatively affect ovulation, the cyclic release of an egg from the ovaries.
- Research shows that obesity in women also lowers the pregnancy rates of in vitro fertilization (IVF) treatment and increases risk of miscarriage.
- Obesity in men can lead to unbalanced hormone levels, resulting in low sperm counts and poor sperm motility (movement).
- Infertility due to weight concerns can sometimes be reversed by bringing body weight into the range of established healthy guidelines (see BMI calculator below).
- The physicians of Fertility Specialists Medical Group encourage our patients to eat a healthy and balanced diet of fresh foods and to participate in moderate physical activity to help maintain a healthy body weight that promotes conception, whether trying to conceive naturally or through fertility treatment.
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How being overweight or underweight can cause infertility in women
How weight affects the menstrual cycle and ovulation
Women who are underweight or overweight may experience infertility due to dysfunctional or absent ovulation (ovulation disorders), which is the release of a mature egg from the ovaries during the regular menstrual cycle. According to the ASRM, 12% of all primary infertility cases are a result of the woman either weighing too little or too much.
The body weight of women affects fertility because of the disruption of typical cyclic hormonal patterns. Because of this and other complex hormone interactions, extra or too little weight impairs the menstrual cycle and ovulation.
Classifying weight through BMI
Weight can be classified by the body mass index, or BMI, which is a measure of body fat based on height and weight that applies to adult men and women.
- A BMI of less than 19 is considered underweight.
- A BMI over 25 is considered overweight.
- A BMI greater than 30 is considered obesity.
When a woman is underweight
- According to ASRM, women with a BMI less than 19 take four times longer to conceive when compared with those with a normal BMI.
- Underweight women essentially “shut down” their reproductive cycle. Hormones in the brain and ovaries do not communicate, and they become hypoestrogenic (lacking in estrogen). This can lead to irregular or absent menstrual cycles as well as issues with bone loss.
- One of the first signs that being underweight is affecting fertility can be irregular menstrual cycles (periods) or no cycles at all.
- In general, an underweight woman must gain two pounds more than the weight at which she stopped having her period to resume menstruation. This can be done in a healthy way, and FSMG can provide resources to assist, either via a nutritionist or a reproductive psychologist.
- Individuals looking to gain weight should focus on healthy fats and complex carbohydrates rather than high-calorie, simple carbohydrates. (See nutrition information and tips below.)
When a woman is overweight
- ASRM notes women with a BMI greater than 35 take twice as long to conceive as women within healthy weight ranges.
- Overweight and obese women have an excess of estrogen and often androgens, which disrupts their ovulation cycle. Women with a BMI greater than 30 are at an increased risk of having irregular or absent menstrual cycles.
- Even modest weight reduction of 5-10% in obese patients can be enough to restore ovulation and increase chances of pregnancy.
- Weight reduction should be gradual and consistent, at a maximum of approximately two pounds per week. Weight loss can be achieved through exercise and a healthy diet. (See nutrition and exercise information and tips below.)
Lower success with fertility treatment
When a woman is overweight or obese, it not only reduces the natural ability to conceive but also reduces the effectiveness of infertility treatments, such as in vitro fertilization (IVF).
- A 25-year-old woman within a healthy BMI range has a 70% chance of success with IVF.
- But a 25-year-old woman with a BMI of 40 (considered obese) only has a 30% chance of success with IVF.
How being overweight can cause infertility in men
How weight affects sperm quality and quantity
Men can also experience infertility due to being obese or overweight. Obesity causes testosterone levels to drop, lowering sperm count and causing poor sperm motility, both of which can lead to difficulties with achieving pregnancy.
- Numerous studies featured from the National Institutes of Health show an association of male infertility with obesity.
- The primary cause of infertility is the disruption of mature sperm development, known as spermatogenesis.
- This results in low sperm quantity, which lowers chances of egg fertilization after intercourse.
- Obesity also impacts sperm motility, which is the ability to move from the vagina to the fallopian tube to meet the egg for fertilization.
- Studies show that semen quality improves with a healthy diet (see nutrition tips below).
Diagnosing weight-related infertility in couples and individuals
If both partners trying to conceive are obese, their fertility as a couple is reduced further.
While not all women or men who are overweight or underweight will experience infertility, we educate all our patients about how they can control the lifestyle factor of weight to give them the best chance to conceive. The negative effects of weight on fertility in men and women can be reversed by maintaining a healthy weight.
How to increase fertility through nutrition & exercise
A healthy, balanced diet composed of fresh foods that are not overly processed is one of the best things men and women can do for their fertility.
Adding an appropriate level of exercise also helps maintain healthy weight, and has additional health benefits.
General tips to help patients achieve their ideal weight include:
- Track calories consumed and calories burned with a food and activity journal or phone app.
- Work with a nutritionist to develop a healthy fertility diet.
- Work with a personal trainer to determine how much exercise per week is needed.
- Men and women should discuss their goal weight with their physician, or with one of our fertility specialists.
Preparing for pregnancy: nutrition & exercise
In addition to a healthy diet, women should ask their doctor about other dietary considerations to support pregnancy, including the following.
- Reducing caffeine intake is important in pregnancy and may also play a role in fertility. The American College of Obstetricians and Gynecologists recommends pregnant women take in no more than 200 mg of caffeine per day. We recommend the same when attempting to conceive.
- A multivitamin containing folic acid (800 mcg) is a good adjunct to dietary nutrition for women and should be started prior to attempting pregnancy.
- We also recommend that those trying to get pregnant consume at least 1,000 mg of calcium a day to support the woman’s nervous, circulatory and musculoskeletal systems.
For optimal fertility, women can seek to maintain an ideal weight by exercising regularly.
- Excessive exercise (exercise that burns more than 2,000-4,000 calories per week) may impair ovulation in some women.
- It is important to also strength train. Body fat affects hormone balance, so having more lean muscle mass than body fat is important.
FSMG recommended resources on nutrition
Good, whole nutrition and a healthy BMI are the keys to overall health, but we recognize that there is not one lifestyle or diet that works for everyone.
Listed below are several resources with different philosophies regarding health and weight loss.
- Elizabeth Shaw, registered dietitian: Nutrition advice based on facts, not fads.
- Tara Coleman, clinical nutritionist: Nutrition made simple.
- The Eating Academy: A blog with a scientific approach to weight loss and overall health.
- Coursera: Free online courses on food, nutrition, health and a wealth of other topics!
- Forks Over Knives: Documentary researching the benefits of a plant-based diet.