Why does being overweight decrease fertility?

As someone who's hoping to conceive soon, you've probably read or heard that weight can have an impact on fertility. You might be wondering how much of an effect weight has, and why it can be a factor that stands in your way when you're trying to get pregnant. 

Does weight really matter for fertility?

The short answer: yes. The long answer: There are numerous studies showing that the chances of getting pregnant and giving birth go down significantly as your weight increases. This is particularly true for people undergoing assisted reproduction. One recent study looking at more than 20,000 fresh donor oocyte cycles concluded that, "there is a progressive and statistically significant worsening of outcomes in groups with higher [recipient] BMI with respect to clinical pregnancy and live birth rate," (Provost et al., 2016).

Why? 

Here are three reasons why extra weight may decrease your fertility (if you have a uterus!):

1. Excess weight can throw off your estrogen levels

Fat produces a form of estrogen. As your weight increases, you have more adipose tissue (fat cells). The extra estrogen produced by your fat cells can disrupt your hormone signalling mechanisms, potentially interfering with ovulation and/or the development of your follicles. The more fat cells you have, the more likely this will be problematic for your fertility.  

2. Excess weight can increase inflammation throughout your body

Fat is inflammatory. We often think of fat cells as inert cells that simply stash away extra energy for later. However, they're not just storage closets! These cells are metabolically active, producing hormones and other signalling molecules that affect the entire body. When your excess weight is around your abdomen (versus on your hips/thighs/butt) it is more inflammatory and more likely to be problematic in terms of your risk of insulin resistance, type II diabetes and other forms of metabolic disease. Inflammation changes the way your oocytes (eggs) develop and decreases your chances of conception. 

3. Excess weight can be a sign of underlying hormonal or metabolic issues that interfere with fertility

Excess weight is often associated with an underlying medical condition, such as polycystic ovarian syndrome (PCOS), thyroid disease, or insulin resistance/type II diabetes. Having one of these conditions, even if your weight is "normal," can interfere with your fertility. It's important to address these directly with your primary care provider, gynecologist or endocrinologist.

Ugh. What can I do?

The good news is that losing even a relatively small amount of weight (5-10% of total body weight) may improve your chances of getting pregnant significantly. You may already have an idea of what you'd like to do to lose weight. It's fine to give it a shot on your own. Here are a few things to keep in mind:

  • Don't restrict your caloric intake too much: very low-calorie diets may actually impair fertility
  • Steer clear of extreme diets unless you have a medical reason for doing them: high-fat diets and/or extremely low-carbohydrate diets are not suitable for pre-conception (If you decide to try one of these, please promise me you'll schedule at least one visit with a nutritionist/dietitian familiar with preconception nutrition!)
  • Get treatment for any underlying conditions: If you suspect you may have an underlying medical condition that is affecting your weight, please check in with your primary care provider before branching out on your own!
  • Set a short-term goal and a specific time frame: It's really important to know sooner rather than later whether you're on the right track. Pick a realistic short-term goal (e.g. I'm going to lose 10 lb in the next two months). Figure out what you're going to do to meet that goal, and write the steps in the calendar along with your end-date. If that date rolls around and you aren't where you want to be, considering working with a professional or trying something different. 

Don't want to be on your own? Plan not working?

If you're not interested in trying to lose weight on your own, or if your current plan just isn't working, you're more than welcome to join me for my preconception weight loss course or private fertility-friendly weight loss support. I'd love to work with you! 

Camille

Hi there. I'm Camille Freeman. I've been a licensed nutritionist since 2006, specializing in working with people who are trying to conceive. I'm also a professor at the Maryland University of Integrative Health, where I teach physiology and pathophysiology in the Department of Nutrition. I like reading, pointed looks, and anything to do with flowers (except the spray-painted kind.)

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